Imaging optical system, projection device, and imaging device

Abstract

[Problem] To obtain an image-forming optical system whereby it is possible to prevent performance fluctuation such as defocusing due to absorption of light by a lens positioned close to a diaphragm. [Solution] An image-forming optical system (100) includes a first optical system (OP1) in which a first dioptric system (R1) is positioned on the reduction side and a second dioptric system (R2) is positioned on the enlargement side of an intermediate image (Im1) as a boundary, the first dioptric system (R1) having a first diaphragm (AS1), and the second dioptric system (R1) having a second diaphragm (AS2). A lens surface is positioned adjacent to each of the first diaphragm (AS1) and the second diaphragm (AS2) on both the reduction side and the enlargement side, and conditions such as 1.5 < Y1-1 (units: mm) are satisfied. In the aforementioned condition, Y1-1 is the absolute value of the beam height of the principal ray at the most peripheral angle of view among the light rays emitted from the lens surface adjacent on the reduction side of the first diaphragm (AS1).

Description

[Technical Field]

[0001] The present invention relates to an imaging optical system, and further to a projection device and an imaging device that use the imaging optical system. [Background technology]

[0002] Various reflective projection devices have been proposed that aim to increase the size of the projection screen and reduce the projection space. For example, Patent Documents 1 to 3 disclose imaging optical systems for projection devices that have a first optical system made up of a refractive optical system and a second optical system including a reflective surface arranged from an image display element (light valve) toward the projection screen, that is, from the reduction side toward the enlargement side.

[0003] Recently, in the projection devices described above, the light sources have become more powerful and generate more heat in response to demands for higher brightness, which means that the imaging optical system is prone to become hot. As a result, when an achromatic lens that corrects chromatic aberration is used in the imaging optical system, the bonded members are prone to discoloration, peeling, and other damage due to heat and light. Patent Document 3 also proposes a configuration for suppressing the decrease in transmittance in such achromatic lenses. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6313865 [Patent Document 2] Patent No. 5728202 [Patent Document 3] International Publication No. 2020 / 008942 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the imaging optical system used in conventional reflective projection devices, the entire high-intensity light beam is focused near the aperture provided inside, and it is recognized that the lens located near the aperture absorbs light and becomes hot, resulting in performance fluctuation problems such as focus deviation.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide an imaging optical system that can prevent performance fluctuations such as focus deviations caused by light absorption by lenses located near the aperture. Another aim of the present invention is to provide a projection device and an imaging device that use such an imaging optical system and in which performance fluctuations are prevented. [Means for solving the problem]

[0007] The imaging optical system according to the present invention comprises: In an imaging optical system that forms an image on a reduction-side conjugate plane on a magnification-side conjugate plane, the imaging optical system includes a first optical system that includes an intermediate image therein and that has a first refractive system disposed on the reduction side of the intermediate image and a second refractive system disposed on the magnification side thereof, the first refractive system has a first aperture, and the second refractive system has a second aperture; Lens surfaces are arranged adjacent to the first and second apertures on both the reduction side and the enlargement side, It is characterized by satisfying the following formulas (1) to (4): "Adjacent" here means that the objects are installed next to each other, and does not necessarily mean that the adjacent objects are "contacting" each other. 1.5 < Y1-1 (1) 1.5 < Y1-2 (2) 1.0 < Y2-1 (3) 0.5 < Y2-2 (4) however, Y1-1: Absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 1 adjacent to the reduction side of the first aperture (unit: mm), Y1-2: Absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays incident on the lens surface 2 adjacent to the enlargement side of the first aperture (unit: mm), Y2-1: Absolute value of the height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 3 adjacent to the reduction side of the second aperture (unit: mm), Y2-2: Absolute value of the height of the chief ray at the most peripheral angle of view of the light rays incident on the lens surface 4 adjacent to the enlargement side of the second aperture (unit: mm)

[0008] Here, the most peripheral angle of view refers to the angle of view farthest from the optical axis, and the chief ray of the most peripheral angle of view refers to the chief ray of the emitted light beam emitted from the position farthest from the intersection of the line extending the optical axis of the first refractive system and the plane including the surface of the image display element within the effective display area of ​​the image display element.

[0009] Within the range defined by the above formula (1), it is more preferable that 2.0<Y1-1, and even more preferable that 2.5<Y1-1. Within the range defined by the above formula (2), more preferably 2.0<Y1-2, and even more preferably 2.5<Y1-2. Within the range defined by the above formula (3), it is more preferable that Y2-1 is 1.5<Y2-1, and even more preferable that Y2-1 is 2.0<Y2-1. Within the range defined by the above formula (4), it is more preferable that 1.0<Y2-2, and even more preferable that 1.5<Y2-2.

[0010] In the imaging optical system of the present invention, it is desirable that the above Y1-1, Y1-2, Y2-1, and Y2-2 and the focal length fw of the entire system at the wide-angle end and at the closest focusing satisfy the following expressions (5) to (8). 0.5 < Y1-1 / |fw| (5) 0.5 < Y1-2 / |fw| (6) 0.3 < Y2-1 / |fw| (7) 0.1 < Y2-2 / |fw| (8)

[0011] Within the range defined by the above formula (5), it is more preferable that 0.6<Y1-1 / |fw|, and even more preferable that 0.7<Y1-1 / |fw|. Furthermore, within the range defined by the above formula (6), 0.6<Y1-2 / |fw| is more preferable, and 0.7<Y1-2 / |fw| is even more preferable. Furthermore, within the range defined by the above formula (7), 0.4 < Y2-1 / |fw| is more preferable, and 0.5 < Y2-1 / |fw| is even more preferable. Furthermore, within the range defined by the above formula (8), 0.2 < Y2-2 / |fw| is more preferable, and 0.3 < Y2-2 / |fw| is even more preferable.

[0012] In the imaging optical system of the present invention, it is desirable to satisfy the following expressions (9) to (12). 5.0 < D1-1 (9) 5.0 < D1-2 (10) 1.0 < D2-1 (11) 1.0 < D2-2 (12) however, D1-1: Distance from the first aperture to the lens surface 1 adjacent to the reduction side of the first aperture (unit: mm) D1-2: Distance from the first aperture to the lens surface 2 adjacent to the first aperture on the enlargement side (unit: mm) D2-1: Distance from the second aperture to the lens surface 3 adjacent to the reduction side of the second aperture (unit: mm) D2-2: Distance from the second aperture to the lens surface 4 adjacent to the magnification side of the second aperture (unit: mm)

[0013] Within the range defined by the above formula (9), it is more preferable that D1-1 is 7.0<D1-1, and even more preferable that D1-1 is 10.0<D1-1. Furthermore, within the range defined by the above formula (10), D1-2 is more preferably 7.0<D1-2, and even more preferably 10.0<D1-2. Furthermore, within the range defined by the above formula (11), it is more preferable that D2-1 is 2.0<D2-1, and even more preferable that D2-1 is 3.0<D2-1. Furthermore, within the range defined by the above formula (12), it is more preferable that D2-2 is 2.0<D2-2, and even more preferable that D2-2 is 3.0<D2-2.

[0014] In the imaging optical system of the present invention, it is desirable to satisfy the following formula (13). Ds2 < Ds1 (13) however, Ds1: D1-1 + D1-2 Ds2: D2-1 + D2-2

[0015] In the imaging optical system of the present invention, it is desirable to satisfy the following expressions (14) to (16). 1.0 < tanθ1×|fw| < 3.0 ···(14) 2.5 < tanθ2×|fw| < 6.0 ···(15) 1.5 < tanθ2 / tanθ1 < 4.0 (16) however, θ1 is the angle of incidence of the chief ray at the most peripheral angle of view to the first aperture. θ2 is the angle of incidence of the chief ray at the most peripheral angle of view to the second aperture. fw is the focal length of the entire system at the wide-angle end and closest focusing

[0016] Within the range defined by the above formula (14), it is more preferable that 1.5 < tanθ1×|fw| < 2.5. Furthermore, within the range defined by the above formula (15), it is more preferable that 3.0 < tanθ2×|fw| < 5.5.

[0017] When the above formulas (14) to (16) are satisfied, it is desirable that the following formula (17) be further satisfied. 5.9 < Ds1 × tanθ1 < 20.0 (17) It is more preferable that, within the range defined by the above formula (17), 7.0<Ds1×tanθ1<18.0.

[0018] Furthermore, when the above formulas (14) to (16) are satisfied, it is also desirable that the following formula (18) be satisfied. 8.0 < Ds2 × tanθ2 < 30.0 (18) It is more preferable that, within the range defined by the above formula (18), 10.0<Ds2×tanθ2<25.0.

[0019] In the imaging optical system of the present invention, it is desirable to satisfy the following expressions (19) and (20). 0.9 ≦ φs1-1 / φs1 <2.0 ···(19) 0.9 ≦ φs1-2 / φs1 <2.0 ···(20) however, φs1: First aperture diameter φs1-1: Effective diameter of the lens adjacent to the first aperture on the reduction side φs1-2: Effective diameter of the lens adjacent to the first aperture on the magnification side

[0020] When the above expressions (19) and (20) are satisfied, it is desirable that the following expressions (21) and (22) be further satisfied. 0.8 ≦ φs2-1 / φs2 <2.5 ···(21) 0.8 ≦ φs2-2 / φs2 <2.5 ···(22) however, φs2: aperture diameter of the second aperture φs2-1: Effective diameter of the lens adjacent to the second aperture on the reduction side φs2-1: Effective diameter of the lens adjacent to the second aperture on the magnification side

[0021] It is desirable that the imaging optical system of the present invention satisfies the following formula (23). 0.5 < Y2-2 × tanθ2 (23)

[0022] Moreover, it is desirable that the imaging optical system of the present invention satisfies the following formula (24): 0.5 < D2-2 / Y2-2 (24)

[0023] In the imaging optical system of the present invention, it is desirable that the first adjacent lens adjacent to the aperture stop and the second adjacent lens adjacent to the first adjacent lens in a direction away from the aperture stop do not include a cemented lens. In this case, it is also desirable that the entire imaging optical system does not include a cemented lens.

[0024] In the imaging optical system of the present invention, two lenses, namely, a first adjacent lens disposed adjacent to the first aperture stop on the reduction side and a second adjacent lens disposed adjacent to the first adjacent lens on the reduction side, are defined as group 1; a first adjacent lens disposed adjacent to the first aperture stop on the magnification side, and a second adjacent lens disposed adjacent to the first adjacent lens on the magnification side, the two lenses being group 2; a first adjacent lens disposed adjacent to the second aperture stop on the reduction side, and a second adjacent lens disposed adjacent to the first adjacent lens on the reduction side, the two lenses being grouped as group 3; When two lenses consisting of a first adjacent lens arranged adjacent to the second aperture stop on the enlargement side and a second adjacent lens arranged adjacent to the first adjacent lens on the enlargement side are grouped as group 4, It is desirable that the lenses included in groups 1, 2, 3, and 4 satisfy the following formula (25) or (26). 40≦νd and 0.97<τ420 (25) νd<40 and 0.90<τ420 (26) however, νd: Abbe number of the optical material (glass material; the same applies below) that makes up the lens τ420: Internal transmittance of an optical material with a thickness of 10.0 mm at a wavelength of 420 nm More specifically, τ420 is the ratio of the amount of light emitted when a 420 nm wavelength light beam is incident on and emitted from a 10.0 mm thick flat lens made of the glass material that makes up the lens perpendicular to the surface, with the amount of incident light being 1. If equation (26) is satisfied, νd<40 and 0.93<τ420 (27) It is more preferable that

[0025] In the imaging optical system of the present invention, when the temperature coefficient of the relative refractive index of the optical material is dn / dt, It is desirable that all the lenses in the lens group satisfy the following formula (28). |dn / dt| < 6.5 (28) Here, the temperature coefficient of the relative refractive index refers to the change in the refractive index of an optical material at the d-line (wavelength 587.6 nm) per 1°C temperature change. The applicable temperature range is 0°C to 20°C. Within the range defined by the above formula (28), |dn / dt| < 6.0 is more preferable, It is more preferable that |dn / dt| < 5.5.

[0026] In the imaging optical system of the present invention, It is desirable that at least one of the positive lenses arranged on the reduction side of the first aperture satisfy the following formula (29): 65.0<νd and 0.005<θg,F (29) however, νd: Abbe number at d line (wavelength 587.6 nm) of the optical material of the positive lens θg,F: Anomalous dispersion of the optical material of the positive lens Within the range defined by the above formula (29), it is preferable that 65.0<νd and 0.010<θg,F, and it is more preferable that 65.0<νd and 0.020<θg,F.

[0027] If the above formula (29) is satisfied, Of the positive lenses arranged on the reduction side of the first aperture, at least two lenses preferably satisfy 65.0<νd and 0.010<θg,F, and more preferably 65.0<νd and 0.020<θg,F.

[0028] In the imaging optical system of the present invention, It is desirable that at least one of the positive lenses arranged on the enlargement side of the first aperture satisfy the following formula (30): 65.0<νd and 0.005<θg,F (30) Within the range defined by the above formula (30), it is preferable that 65.0<νd and 0.010<θg,F, and it is more preferable that 65.0<νd and 0.020<θg,F.

[0029] If the above formula (30) is satisfied, At least two of the positive lenses arranged on the enlargement side of the first aperture are of the following formula: 65.0<νd and 0.005<θg,F It is more preferable that, within the range defined by this formula, More preferably, 65.0<νd and 0.010<θg,F; Even more preferably, 65.0<νd and 0.020<θg,F.

[0030] The imaging optical system of the present invention further comprises: It includes one or more zoom groups (magnification-varying groups) that move when changing magnification, Among the zoom groups on the reduction side of the first refractive system's aperture stop, the first zoom group having the largest number of lenses has a positive focal length, It is desirable that the first zoom group does not include a lens on the enlargement side of the first aperture, but includes a lens on the reduction side.

[0031] In the above configuration, it is also desirable to have a fixed group 1 with a positive focal length that does not move during zooming located at the most reduction side of the imaging optical system. Such a fixed group 1 should preferably include at least one negative lens.

[0032] When the image-forming optical system includes one or more zoom groups that move during magnification variation as described above, it is desirable that the image-forming optical system further includes a second zoom group that is adjacent to the first aperture stop on the enlargement side, and that the second zoom group be made up of a positive lens.

[0033] It is desirable that the positive lens constituting the second zoom group as described above be a positive meniscus lens with a concave surface facing the image side, and that the first zoom group and second zoom group as described above move independently during zooming.

[0034] Furthermore, when the first and second zoom groups are provided as described above, it is desirable that the final zoom group, which is the zoom group on the most magnifying side among the zoom groups, includes a negative lens.

[0035] It is desirable that the negative lens be disposed on the magnification side of the final zoom group. It is also desirable that the final zoom group be composed only of negative lenses. When the final zoom group is composed only of negative lenses, it is desirable that a fixed group 2 be disposed adjacent to the magnification side of the final zoom group. It is desirable that such a fixed group 2 include a negative meniscus aspherical lens. When the fixed group 2 includes a negative meniscus aspherical lens as described above, it is desirable that the negative meniscus lens included in the first refractive system has a central to peripheral lens thickness ratio (non-uniform thickness ratio) of 1.5 or more. This makes it possible to avoid the occurrence of ghost light.

[0036] The imaging optical system according to the present invention comprises: It has at least one focus group that moves when focusing, At least one focus group includes a reduction-side focus group disposed in the first refractive system. It is desirable.

[0037] In the above case, it is desirable that the imaging optical system includes at least two groups and is configured to perform floating focus. In this configuration, it is desirable that at least one of the focus groups includes a magnification-side focus group disposed in the second refractive system.

[0038] It is desirable that the at least one focus group includes an intermediate focus group including the most enlargement lens of the first refractive system and the most reduction lens of the second refractive system, and that an intermediate image is formed within this intermediate focus group.

[0039] In addition, the above intermediate focus group is A positive meniscus lens with its convex surface facing the magnification side is placed on the reduction side of the intermediate image, A positive meniscus lens with its convex surface facing the reduction side is positioned on the magnification side of the intermediate image. It is desirable that Furthermore, it is desirable that the intermediate focus group further includes a negative meniscus lens disposed between the meniscus lens with its convex surface facing the enlargement side and the intermediate image.

[0040] Furthermore, as described above, when there is at least one focus group that moves during focusing, and at least one focus group includes a reduction-side focus group disposed in the first refractive system, it is desirable that the final focus group disposed on the most enlargement side be disposed adjacent to the reduction side of the second aperture. It is also desirable that the final focus group be composed of three lenses: positive, negative, and positive.

[0041] Furthermore, as mentioned above, if there is at least one focus group that moves during focusing, and at least one focus group includes a reduction-side focus group that is arranged in the first refractive system, it is desirable that the lens group on the enlargement side of the second aperture be made up of a fixed group 3 that does not move during zooming or focusing.

[0042] Furthermore, the imaging optical system according to the present invention preferably includes a second optical system including a reflective optical element disposed on the magnification side of the first optical system. In this case, the second optical system preferably includes a concave mirror, and the concave mirror is preferably disposed on the magnification side of a second intermediate image formed by the imaging action of the first optical system.

[0043] The reflective optical element includes a prism having a solid structure and a total internal reflection surface; The prism has two reflecting surfaces, and all incident light is transmitted to the next surface by total reflection at either surface. the prism is disposed between the first optical system and the concave mirror; It is desirable. It is also preferable that the angle of the inclined surface of the reflecting surface of the prism is greater than 45° with respect to the optical axis.

[0044] On the other hand, the projection device according to the present invention the imaging optical system according to the present invention as described above; an image display element disposed at a reduction-side conjugate plane position of the imaging optical system; It has the following characteristics.

[0045] Furthermore, the imaging device according to the present invention comprises: the imaging optical system according to the present invention as described above; an image sensor disposed at a reduction-side conjugate plane of the imaging optical system; It has the following characteristics. [Effects of the Invention]

[0046] The imaging optical system according to the present invention satisfies the above-mentioned formulas (1) to (4), and the larger the values ​​of Y1-1, Y1-2, Y2-1, and Y2-2, which are defined by formulas (1) to (4), the farther the lenses are from the aperture. Therefore, by setting these values ​​to the extent defined by formulas (1) to (4), it is possible to reduce light absorption by lenses located near the aperture, which are prone to become hot. This makes it possible to prevent performance fluctuations in the imaging optical system due to heat generation caused by light absorption by these lenses.

[0047] More specifically, because light rays entering the aperture are essentially concentrated, they are also likely to be incident on the lenses before and after it, resulting in excessive optical energy concentration on the lenses. To address this issue, by specifying the height of the chief ray at the most peripheral angle of view on lens surfaces 1 and 3, which emit light rays toward the aperture, and lens surfaces 2 and 4, on which light rays emitted from the aperture are incident, it is possible to disperse the light rays entering or exiting each lens surface without concentrating them. This prevents excessive concentration of optical energy and reduces fluctuations in the optical performance of each lens.

[0048] Furthermore, particularly when formulas (5) to (8) are satisfied, the values ​​defined by formulas (1) to (4) are further divided by the focal length at the wide-angle end and the closest focusing distance, making it possible to accurately define the ray height in the range of use where performance fluctuations are most likely to occur.

[0049] Furthermore, when formulas (9) to (12) are satisfied, the effects of heat and light on the lens can be more reliably suppressed. To explain in more detail, the aperture in the imaging optical system converts light energy into heat when eliminating unnecessary light rays, so lenses near the aperture are more susceptible to the effects of heat. Furthermore, the closer to the aperture, the more concentrated the light rays are, so optical energy tends to concentrate. Therefore, by specifying the distance between the aperture and the lens surface adjacent to the aperture in accordance with formulas (9) to (12), it is possible to prevent the aperture and the lens surface adjacent to the aperture from being too close to each other, thereby suppressing the effects of heat and light.

[0050] Furthermore, the above-mentioned formulas (13) to (16) express the geometric relationship between the first refractive system, which is located on the reduction side of the intermediate image, and the second refractive system, which is located on the enlargement side. For example, by making the incident angle θ2 to the second diaphragm larger than the incident angle θ1 to the first diaphragm, and by making the distance Ds2 between the adjacent lenses before and after the diaphragm in the second diaphragm smaller than the distance Ds1 between the adjacent lenses before and after the diaphragm in the first diaphragm, the load on each lens due to light rays can be reduced, and the overall length of the second diaphragm can be shortened. By shortening the overall length of the second diaphragm in this way, the first diaphragm can be made sufficiently long, which in turn ensures sufficient movement of the lens groups during focusing (focus stroke) and zooming (zoom stroke). This makes it possible to obtain an imaging optical system with high performance.

[0051] In particular, by satisfying equation (13), that is, by making the distance Ds1 between the adjacent lenses before and after the aperture of the first refractive system greater than the distance Ds2 between the adjacent lenses before and after the aperture of the second refractive system, it is possible to make the surrounding lenses less susceptible to the influence of light, even when the first aperture is prone to receiving stronger light rays when light rays are incident from the reduction side conjugate surface.

[0052] Furthermore, the value of tan θ1 × |fw| defined in Equation (14) is the ratio of the tangent of the angle of incidence θ1 of the chief ray at the most peripheral angle of view onto the first aperture to the focal length. If this value is too small, the angle of incidence θ1 becomes too small, making it difficult to separate on-axis rays from off-axis rays. This requires a larger distance between the first aperture and the lens, resulting in a longer overall lens length. On the other hand, if this value is too large, the angle of incidence θ1 becomes too large, increasing the effective diameter of the lens adjacent to the aperture, resulting in a larger optical system. Furthermore, the need to refract light rays significantly increases the aberrations that occur. On the other hand, if the value falls within the range defined in Equation (14), the overall lens length can be prevented from increasing, which is advantageous for miniaturizing the imaging optical system. The same can be said about the value of tan θ2 × |fw| defined in Equation (15) in relation to the second aperture.

[0053] Equation (16) defines the balance between the incident angle θ1 of the light beam at the first aperture stop and the incident angle θ2 of the light beam at the second aperture stop. If the value of tan θ2 / tan θ1 is outside the range defined by equation (16), the overall length of the first or second refractive system increases. Specifically, if the incident angle θ1 exceeds the upper limit, the overall length of the first refractive system increases excessively. If the incident angle θ2 increases excessively, the lens diameter of the second refractive system increases and the number of lenses increases to suppress excessive aberrations. If the incident angle θ1 exceeds the lower limit, the lens diameter increases and the number of lenses increases to correct excessive aberrations. As a result, it becomes difficult to ensure the lens spacing required for zooming and costs may increase. If the incident angle θ2 decreases excessively, the overall length of the second refractive system increases excessively. If the value of tan θ2 / tan θ1 satisfies the formula (16), it is possible to prevent the overall length of the first refractive system or the second refractive system from increasing and the cost of the imaging optical system from increasing as described above.

[0054] The value of Ds1 × tan θ1 defined in equation (17) represents the distance between the lenses on both sides of the first aperture multiplied by the tangent of the angle of incidence of light onto the first aperture. If this value falls below the lower limit of equation (17), the ray height defined in equation (1) decreases, increasing the impact of light on the optical performance of the imaging optical system. On the other hand, if the value of Ds1 × tan θ1 exceeds the upper limit of equation (17), the overall length of the imaging optical system becomes too long, which is disadvantageous from the perspective of miniaturizing the imaging optical system.

[0055] Furthermore, if the incident angle θ1 of the light beam to the first aperture is too steep, causing the value of Ds1 × tanθ1 to exceed the range specified by Equation (17), the lens power will be strengthened, resulting in increased aberration. Furthermore, the lens diameter at the rear of the lens (the reduction side of the first refractive system aperture) is limited by mechanical constraints such as the projection device. If the distance between the aperture and the lens is too large, or if the incident angle θ1 of the light beam to the first aperture is too steep, it is necessary to narrow (thin) the ray width by cutting off the upper and lower rays of the off-axis ray to ensure off-axis ray coverage while suppressing an increase in the effective diameter of the lens. In other words, the reduction in peripheral illumination may result in a decrease in the peripheral illumination ratio. To avoid these problems, it is necessary to satisfy Equation (17).

[0056] The above has explained the value of Ds1 × tan θ1, the range of which is defined by equation (17). The same can be said for Ds2 × tan θ2, the range of which is defined by equation (18), in relation to the distance to the second aperture stop and the lens surface associated with it.

[0057] Equations (19) and (20) define the effective diameters of the reduction-side lens surface and the magnification-side lens surface of the adjacent lens relative to the aperture diameter of the first aperture. These definitions make it possible to limit the degree of focusing of light rays on the lens surface. If the defined values ​​are below the lower limit of each equation, the focusing of light rays on the lens surface will be too intense, and the lens glass material will be affected by the light energy, resulting in changes in optical performance. Conversely, if the defined values ​​are above the upper limit of each equation, the effective diameter of the lens will become too large, resulting in an increase in the overall size of the optical system. Satisfying equations (19) and (20) prevents such problems from occurring.

[0058] Formulas (21) and (22) define the effective diameters of the reduction-side lens surface and the magnification-side lens surface of the adjacent lens relative to the aperture diameter of the second diaphragm. In this case, if formulas (21) and (22) are satisfied, the same effect as when formulas (19) and (20) are satisfied can be obtained.

[0059] Equations (23) and (24) are restatements or supplements of the above (distance between the aperture and the lens, the angle of incidence of the light beam on the aperture, and the height of the light beam). If these equations (23) and (24) are satisfied, it is possible to reduce the load caused by the light beam on the lens near the aperture.

[0060] The absence of cemented lenses is particularly desirable when the imaging optical system is used in, for example, a high-brightness projector. That is, when the imaging optical system is used in a high-brightness projector, the optical surface is irradiated with particularly high-power blue light, which tends to deteriorate the adhesive. Therefore, in order to ensure the durability of the imaging optical system, it is preferable to not include cemented lenses that use adhesives.

[0061] As mentioned above, the problem of lenses located near the aperture diaphragm absorbing light and changing optical performance, resulting in out-of-focus images, is particularly pronounced for light on the short wavelength side, such as blue light. Therefore, it is necessary to use a glass material with a high τ420 for lenses located near the aperture diaphragm. However, glass materials with a high τ420 tend to have a high Abbe number νd, which is disadvantageous for correcting chromatic aberration. Therefore, by specifying the Abbe number νd for each lens located adjacent to the first aperture diaphragm on the reduction side and magnification side so that it satisfies equations (25) and (26), it is possible to design a lens configuration that suppresses absorption of light on the short wavelength side, such as blue light, while providing the necessary aberration correction capabilities.

[0062] Furthermore, equation (28) defines the temperature coefficient of the glass material. Because the aperture diaphragm blocks unwanted light rays and can absorb light and generate heat, and the lens glass material itself can also absorb some of the light energy and generate heat, lenses placed near the aperture are susceptible to the effects of heat. Therefore, by limiting the temperature coefficient of the refractive index of the lens glass material to a certain value or less, it is possible to prevent focus shifts that occur when lenses near the first or second aperture are heated by light energy.

[0063] Glass materials with a high τ420 used in lenses placed near the aperture generally tend to have a high Abbe number νd. Excessive use of glass materials with a high Abbe number νd in this way can result in insufficient correction of aberrations, particularly chromatic aberrations. To solve this problem, for the positive lenses placed near the first aperture, glass materials with high anomalous dispersion characteristics (i.e., high θg,F) as defined by equations (29) and (30) can be used, which makes it possible to appropriately correct insufficient chromatic aberrations.

[0064] In the present invention, the overall length of the first refractive system can be increased by appropriately setting the angle of incidence of light rays on the aperture stop. By appropriately arranging the zoom group in the space created by this, a zoom lens with high-quality optical performance can be achieved.

[0065] In particular, in order to make the imaging state on the reduction side of the imaging optical system telecentric in both WIDE and TELE, it is preferable that the unit closest to the reduction side be the fixed unit 1 having a positive focal length.

[0066] If the fixed group 1 is made up of a single positive lens, various aberrations will occur to a large extent, so it is more preferable that the fixed group 1 be made up of a plurality of lenses, and it is preferable that it include a negative lens.

[0067] The group with the largest number of lenses, located on the reduction side of the first aperture, has the effect of determining the zoom ratio (variable magnification), and if this group has a positive focal length, it is preferable in terms of shortening the movement distance. [Brief explanation of the drawings]

[0068] [Figure 1] FIG. 1 is a cross-sectional view showing the lens configuration of the imaging optical system of Example 1 together with the main light beams. [Figure 2] 1 is a cross-sectional view showing the imaging optical system of Example 1 in a wide-angle end state (upper) and a telephoto end state (lower); [Figure 3] FIG. 1 is a cross-sectional view showing the optical elements constituting the imaging optical system of Example 1 in one magnification and focusing state. [Figure 4]FIG. 1 is a cross-sectional view showing the optical elements constituting the imaging optical system of Example 1 in another magnification / focusing state. [Figure 5] FIG. 1 is a diagram showing basic data of optical elements constituting the imaging optical system of Example 1. [Figure 6] 1 shows aspheric data of the lenses constituting the imaging optical system of Example 1. [Figure 7] 1 shows aspheric data of the concave mirror that constitutes the imaging optical system of Example 1. [Figure 8] 1A and 1B are diagrams showing the movement amounts of the zoom group and the focus group in the imaging optical system of Example 1 when one zoom group moves in one mode (1) and when another zoom group moves in another mode (2). [Figure 9] Graphs showing spherical aberration (left), astigmatism (center), and distortion (right) when the imaging optical system of Example 1 is in the wide-angle end state (1) and the telephoto end state (2). [Figure 10] Graph showing lateral aberration at the wide-angle end of the imaging optical system of Example 1 [Figure 11] Graph showing lateral aberration at the telephoto end of the imaging optical system of Example 1 [Figure 12] FIG. 10 is a cross-sectional view showing the lens configuration of the imaging optical system of Example 2 together with the main light beams. [Figure 13] FIG. 10 is a cross-sectional view showing the lens configuration of the imaging optical system of Example 2 in the wide-angle end state. [Figure 14] FIG. 10 is a diagram showing basic data of optical elements constituting the imaging optical system of Example 2. [Figure 15] FIG. 10 is a diagram showing aspheric surface data of lenses constituting the imaging optical system of Example 2. [Figure 16] Graph showing lateral aberration of the imaging optical system of Example 2 [Figure 17] Graphs showing spherical aberration (left), astigmatism (center), and distortion (right) of the imaging optical system of Example 2. [Figure 18] FIG. 10 is a cross-sectional view showing the lens configuration of the imaging optical system of Example 3 together with the main light beams. [Figure 19] FIG. 10 is a cross-sectional view showing the imaging optical system lens configuration of Example 3 in the wide-angle end state. [Figure 20]FIG. 10 is a diagram showing basic data of optical elements constituting the imaging optical system of Example 3. [Figure 21] FIG. 10 is a diagram showing aspheric surface data of lenses constituting the imaging optical system of Example 3. [Figure 22] Graph showing lateral aberration of the imaging optical system of Example 3 [Figure 23] Graphs showing spherical aberration (left), astigmatism (center), and distortion (right) of the imaging optical system of Example 3. [Figure 24] 10A and 10B are cross-sectional views showing the imaging optical system of Example 4 in a wide-angle end state (upper) and a telephoto end state (lower); [Figure 25] FIG. 10 is a cross-sectional view showing the imaging optical system of Example 4, divided into a zoom group and a focus group. [Figure 26] FIG. 10 is a diagram showing basic data of optical elements constituting the imaging optical system of Example 4. [Figure 27] FIG. 10 is a diagram showing aspheric surface data of lenses constituting the imaging optical system of Example 4. [Figure 28] FIG. 10 is a diagram showing the movement amounts of the zoom group and the focus group in the imaging optical system of Example 4. [Figure 29] Graphs showing spherical aberration (left), astigmatism (center), and distortion (right) when the imaging optical system of Example 4 is in the wide-angle end state. [Figure 30] Graph showing lateral aberration when the imaging optical system of Example 4 is in the wide-angle end state [Figure 31] Graphs showing spherical aberration (left), astigmatism (center), and distortion (right) when the imaging optical system of Example 4 is in the telephoto end state. [Figure 32] Graph showing lateral aberration when the imaging optical system of Example 4 is in the telephoto end state [Figure 33] 10A and 10B are cross-sectional views showing the imaging optical system of Example 5 in the wide-angle end state (upper) and the telephoto end state (lower). [Figure 34] FIG. 10 is a cross-sectional view showing the imaging optical system of Example 5, divided into a zoom group and a focus group. [Figure 35] FIG. 10 is a diagram showing basic data of optical elements constituting the imaging optical system of Example 5. [Figure 36]FIG. 10 is a diagram showing aspheric surface data of lenses constituting the imaging optical system of Example 5. [Figure 37] FIG. 13 is a diagram showing the movement amounts of the zoom group and the focus group in the imaging optical system of Example 5. [Figure 38] Graphs showing spherical aberration (left), astigmatism (center), and distortion (right) when the imaging optical system of Example 5 is in the wide-angle end state. [Figure 39] Graph showing lateral aberration when the imaging optical system of Example 5 is in the wide-angle end state [Figure 40] Graphs showing spherical aberration (left), astigmatism (center), and distortion (right) when the imaging optical system of Example 5 is in the telephoto end state. [Figure 41] Graph showing lateral aberration when the imaging optical system of Example 5 is in the telephoto end state [Figure 42] FIG. 1 is a diagram showing values ​​relating to the main configuration of the imaging optical system of the present invention for each embodiment. [Figure 43] FIG. 1 is a diagram showing the names of glass materials of the main lenses in the imaging optical system of the present invention for each embodiment. [Figure 44] A diagram showing the internal transmittance τ420 of the glass material shown in FIG. 43 for each example. [Figure 45] FIG. 44 shows the temperature coefficient dn / dt of the relative refractive index of the glass material shown in FIG. 43 for each example. [Figure 46] FIG. 10 is a diagram showing the anomalous dispersion θg,F of the main lenses in the imaging optical system of the present invention for each embodiment. [Figure 47] FIG. 1 is a diagram illustrating a lens near the aperture in the imaging optical system of the present invention. [Figure 48] FIG. 1 is a schematic diagram illustrating the detailed configuration of an imaging optical system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0069] Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of an imaging optical system 100 according to one embodiment of the present invention, along with the main light beams. FIG. 1 shows the imaging optical system 100 at the wide-angle end. FIG. 2 shows the imaging optical system 100 at the wide-angle end, excluding the light beams, in the upper row, labeled "WIDE," and the imaging optical system 100 at the telephoto end, labeled "TELE," in the lower row. FIGS. 3 and 4, which will be described later, also show the imaging optical system 100 at the wide-angle end. In these figures, the left side is the reduction side and the right side is the magnification side. However, taking into account the direction of travel of the light beams, the magnification side may be referred to as the front and the reduction side as the rear. This imaging optical system 100 corresponds to Example 1, which will be described later.

[0070] As an example, the imaging optical system 100 is applied to a projection device (projector) that enlarges and projects an image displayed on the image display surface 1 of the image display element 2. The imaging optical system 100 is basically composed of a first optical system OP1 and a second optical system OP2 arranged on the enlargement side of the first optical system OP1. The first optical system OP1 includes a first refractive system R1 and a second refractive system R2. The first refractive system R1 generates an intermediate image Im1, and the second refractive system R2 is arranged on the enlargement side of the first refractive system R1, with the intermediate image Im1 interposed therebetween. Meanwhile, the second optical system OP2 includes a concave mirror 6, which is a reflective optical element. The cross-sectional view shown in FIG. 1 is a cross-sectional view of the imaging optical system 100 cut along a plane including the optical path of the chief ray of a light beam emitted from the center of the effective projection area of ​​the image display surface 1 of the image display element 2 until it reaches the projection screen. In Fig. 1, the reduction side of the imaging optical system 100 is closest to the image display element 2, i.e., the rearmost lens L1, and the magnification side is closest to the frontmost lens L27. G1, G2, G3, and G4 in Fig. 1 respectively represent Group 1, Group 2, Group 3, and Group 4, which will be described later. The notation methods in Figs. 1 and 2 described above are also the same in Figs. 12 and 13, which show an imaging optical system 200 of Example 2, and Figs. 18 and 19, which show an imaging optical system 300 of Example 3, which will be described later.

[0071] In FIG. 1, the chief ray (near-end chief ray) of the light rays emitted from the position closest to the optical axis Z on the image display surface 1 of the image display element 2 is indicated by a dashed-dotted line. Above and below this chief ray, upper and lower rays are indicated by solid lines, representing the spread of light rays emitted from the same position as the chief ray but at an angle relative to the chief ray. Furthermore, the chief ray of the light rays emitted from the end of the effective projection area of ​​the image display surface 1 (the lower end in the figure) and the upper and lower rays relative to this chief ray are also indicated. The position where the above-mentioned chief ray, upper ray, and lower ray intersect is the image formation position, and a first intermediate image Im1 and a second intermediate image Im2, described below, are formed at this position. The above-described methods of depicting the chief ray and the upper and lower rays are also used in FIGS. 3, 4, 12, and 18, described below.

[0072] As shown in FIG. 1, a projection device including an imaging optical system 100 is configured by arranging an image display element (light valve) 2 having an image display surface 1, a prism 3, a glass block 4, a first optical system OP1, and a second optical system OP2, in that order from the reduction side to the enlargement side. In this projection device, a light beam emitted from a light source (not shown) and given image information on the image display surface 1 is incident on the first optical system OP1 through the prism 3 and the glass block 4, and a first intermediate image Im1 is formed by the first refraction system R1. The prism 3 is a color synthesis prism such as a dichroic prism or a TIR prism. The light beam is further incident on a second refraction system R2 of the first optical system OP1 and the second optical system OP2, where the first intermediate image Im1 is formed as a second intermediate image Im2 between the prism (glass block) 5 and the concave mirror 6. The second intermediate image Im2 is reflected and enlarged by a second optical system OP2 including a concave mirror 6, and is then enlarged and projected as a projection image onto a screen (not shown).

[0073] 1 and the lens configuration diagrams of Figures 2 to 4, 12, 13, 18, and 19 described below, the first intermediate image Im1 and the second intermediate image Im2 are shown as solid straight lines, showing only their approximate positions on the optical axis Z. However, the actual first intermediate image Im1 and the second intermediate image Im2 are real images that have shapes that tilt (incline) toward the rear, that is, toward the reduction side, as they move away from the chief ray.

[0074] Next, the lenses and other elements constituting the first refraction system R1 and the second refraction system R2 will be described in more detail. The first refraction system R1 is composed of, arranged in order from the reduction side to the enlargement side along the optical axis Z, a biconvex lens L1, a negative meniscus lens L2, a biconvex lens L3, a biconvex lens L4, a biconcave lens L5, a biconvex lens L6, a biconcave lens L7, a positive meniscus lens L8, a first field stop FS1, a first aperture stop AS1, a second field stop FS2, a positive meniscus lens L9, a biconvex lens L10, a negative meniscus lens L11, a biconvex lens L12, a biconcave lens L13, a semi-concave lens L14, a biconvex lens L15, a negative meniscus lens L16, a biconvex lens L17, a positive meniscus lens L18, and a negative meniscus lens L19. A first intermediate image Im1 is formed by the first refraction system R1.

[0075] On the other hand, the second refractive system R2 is configured by sequentially arranging a positive meniscus lens L20, a biconvex lens L21, a negative meniscus lens L22, a biconvex lens L23, a second aperture stop AS2, a positive meniscus lens L24, a negative meniscus lens L25, a biconvex lens L26, and a biconvex lens L27 from the reduction side to the enlargement side along the optical axis Z. The first intermediate image Im1 is further imaged as a second intermediate image Im2 by the second refractive system R2.

[0076] A second optical system OP2 including a prism 5 and a concave mirror 6 is disposed on the magnification side of the second refraction system R2, and the light beam emitted from the second refraction system R2 is incident on this second optical system OP2. As described above, the second intermediate image Im2 is reflected and enlarged by the second optical system OP2, and is then enlarged and projected onto a screen (not shown) as a projected image. The prism 5 has a solid structure and has two total internal reflection surfaces, and all the light beams incident on the prism 5 are totally reflected at both of these surfaces and transmitted to the next surface.

[0077] The lenses and other elements constituting the first optical system OP1 described above are moved along the optical axis Z, either individually or in groups, for zooming (variable magnification) and focusing (focusing). Below, with reference to Figures 3 and 4, we will explain the lens group that moves for zooming, i.e., the zoom group, and the lens group that moves for focusing, i.e., the focus group. In Figures 3 and 4, the lens group that functions as the zoom group (which may include an aperture associated with it) is indicated by "z" followed by group numbers 1 to 5 or 1 to 6, and the lens group that functions as the focus group is indicated by "f" followed by group numbers 1 to 3. Drive mechanisms for moving these lens groups are not shown in Figures 3 and 4.

[0078] The imaging optical system 100 of this embodiment is expected to be applied in two ways: one in which only one zoom group z1 is arranged on the reduction side of the first aperture stop AS1, and this zoom group z1 moves together with the first aperture stop AS1 during zooming (when varying magnification), and the other in which two zoom groups z1 and z2 are arranged on the reduction side of the first aperture stop AS1, and the zoom group z2 moves together with the first aperture stop AS1 during zooming. Figure 3 shows zoom groups z1-5 and focus groups f1-3 in the former case, and Figure 4 shows zoom groups z1-6 and focus groups f1-3 in the latter case.

[0079] Next, detailed data of the components in Example 1 according to an embodiment of the present disclosure will be described with reference to FIGS. 5 to 9. First, FIG. 5 shows basic data of the components in Example 1. In the basic data in FIG. 5, the surface number column indicates the surface number, with 0 representing the surface of the component closest to the reduction side, and the surface number increases sequentially toward the magnification side. Aspheric surfaces among the surfaces with each surface number are indicated with an asterisk (*). In the element column, elements other than lenses L1 to L27 are indicated by abbreviations, and will be described below, starting from the reduction side, with reference to FIG. 1. "OBJ" indicates the surface of the image displayed on the image display surface 1 of the image display element 2, followed by "PR2," "PR3," and "PR4" representing the image display element 2, prism 3, and prism 4, respectively. "FS1," "AS1," and "FS2" represent the first field stop FS1, the first aperture stop AS1, and the second field stop FS2, respectively. "Im1" represents the first intermediate image Im1, and "AS2" represents the second aperture stop AS2. "PR5" refers to prism 5, "Im2" refers to the second intermediate image Im2, and "MIR" refers to concave mirror 6. "IMG" refers to the projected image onto a screen (not shown). The "radius of curvature" column in Figure 5 also lists the paraxial radius of curvature of each surface. The sign of the radius of curvature is positive when the surface shape is convex toward the reduction side and negative when the surface shape is convex toward the magnification side. The "surface spacing" column lists the distance along the optical axis Z between the surface with the given surface number and the surface with the next surface number. This value is for when the imaging optical system 100 is set to the wide-angle end. The value in the optical path from the reduction side toward the concave mirror 6 is treated as a positive value, and the value in the optical path reflected by the concave mirror 6 is treated as a negative value. The effective diameter is twice the effective image height. The above values ​​of radius of curvature, surface spacing, and effective diameter are in millimeters. The columns for glass material, refractive index, and Abbe number show the name of the glass material of each optical element, the refractive index for the d-line (wavelength 587.6 nm), and the Abbe number for the d-line. Note that Figure 5 also shows rounded values ​​as appropriate. The display method in Figure 5 described above is also used in Figures 14, 20, 26, and 35, which will be described later.

[0080] Figure 6 shows the aspherical surface number (No.) and aspherical coefficient as data on aspherical lens surfaces. Note that "En" means "10 to the nth power." The shape of the aspherical surface is expressed as follows: X is the amount of sag of the surface parallel to the optical axis, and R is the radial distance [R=(x 2 +y 2 ) 1 / 2 ], where x and y are coordinates perpendicular to the optical axis and perpendicular to each other, Rdy is the paraxial radius of curvature, and K is the conic constant, this can be expressed by the following equation using the coefficients K, A4, A6, A8, A10, A12, A14, and A16 shown in Figure 6. X=(1 / Rdy)R 2 / [1+{1-(1+K)(1 / Rdy) 2 R 2} 1 / 2 ] +A4R 4 +A6R 6 +A8R 8 +A10R 10 +A12R 12 +A14R 14 +A16R 16 The meanings of "No.", "En", "X", "R", "K" and "Rdy" above are the same in the description of aspherical surfaces to be described later.

[0081] 7 shows aspherical coefficients as data related to the concave mirror 6, whose reflecting surface (surface number 68) is aspherical. The aspherical shape of the reflecting surface of this concave mirror 6 is expressed by the following equation using the aspherical coefficients shown in FIG. X=(1 / Rdy)R 2 / [1+{1-(1+K)(1 / Rdy) 2 R 2} 1 / 2 ] +A3R 3 +A4R 4 +A5R 5 +A6R 6 +A8R 8 +A10R 10 +A12R 12 +A14R 14 +A16R 16

[0082] Next, the movement amounts of the zoom group and focus group described above will be described with reference to FIG. 8. As mentioned above, this embodiment assumes two configurations during zooming: one in which one zoom group z1 moves together with the first aperture stop AS1 (see FIG. 3), and the other in which two zoom groups z1 and z2 move together with the first aperture stop AS1 (see FIG. 4). The movement amounts of the zoom group and focus group in the former case are referred to as first parameters and are shown in FIG. 8(1), and the movement amounts of the zoom group in the latter case are referred to as second parameters and are shown in FIG. 8(2). As will be described later, this movement amount is indicated by the surface spacing between lens surfaces. Note that the movement amount of the focus group is common to both cases, so the movement amount of the focus group is omitted in FIG. 8(2).

[0083] In (1) and (2) of Fig. 8, the column Z indicates the different states of the lens group depending on zooming or focusing. These states are four states 1 to 4 for the first parameter in (1) of Fig. 8, and two states 1 and 2 for the second parameter in (2) of Fig. 8. Also, in (1) and (2) of Fig. 8, the column EFL indicates the effective focal length (unit: mm) of the imaging optical system 100. The column "s + numerical value" following to the right of the EFL column indicates the surface spacing (unit: mm) of the surfaces shown in Fig. 5, and the numerical value indicates the surface number (No.). For example, s11 indicates the surface with surface number No. = 11, that is, the surface in front of lens L3. This indicates the surface spacing of the lens surface relative to the next surface, No. 11. The "ZOOM" notation below each "s + numerical value" column indicates that the surface spacing of that displayed column changes with zooming, and the "FOCUS" notation indicates that the surface spacing of that displayed column changes with focusing. In the first parameter of (1) in Figure 8, states 1 and 2 are states in which the lens is focused on the closest object, such as a screen, within the focusing range, and states 3 and 4 are states in which the lens is focused on the farthest object within the focusing range. Furthermore, states 1 and 3 are wide-angle end states set by zooming, and states 2 and 4 are telephoto end states set by zooming. In the second parameter of (2) in Figure 8, state 1 is the wide-angle end state, and state 2 is the telephoto end state.

[0084] Next, the detailed configuration of Example 1 and the effects of this configuration will be described. Note that, since this detailed configuration mainly relates to numerical values, for comparison purposes, it is shown together with Examples 2 to 5 described later in Figures 42 to 46. Note that in Figures 42, 44 to 46 showing numerical values, values ​​are also shown that have been rounded as appropriate.

[0085] In Figure 42, "fw" indicates the focal length fw of the entire system when the imaging optical system 100 is in the wide-angle end state. Note that all numerical values ​​shown in Figure 42 are values ​​when the imaging optical system 100 is in the wide-angle end state and focused at the closest distance, and are rounded off as appropriate. Furthermore, unless otherwise noted, all numerical values ​​are in mm. Below these are shown the values ​​of ray heights Y1-1, Y1-2, Y2-1, and Y2-2, whose numerical ranges are defined by the aforementioned equations (1), (2), (3), and (4), respectively. Note that in the following explanation, the numerical values ​​shown in Figure 42 will be explained in order from top to bottom.

[0086] These ray heights will now be explained for clarity with reference to FIG. 47. Ray heights Y1-1 and Y1-2 are absolute values ​​of the ray heights of the chief ray at lens surface 1, located adjacent to the reduction side of the first aperture stop, and lens surface 2, located adjacent to the magnification side. Specifically, in this example, as shown in FIG. 47(1), the lens surfaces on the first aperture stop AS1 side of lens L8, located adjacent to the reduction side of the first aperture stop AS1, and lens surface L9, located adjacent to the magnification side of the first aperture stop AS1, are lens surface 1 and lens surface 2, respectively. The chief ray at the most peripheral angle of view that emerges from lens surface 1 and enters lens surface 2 is shown as a ray that forms an angle of incidence θ1 with lens surface 2 (a surface perpendicular to the optical axis Z). Note that this most peripheral angle of view is as described above. These ray heights Y1-1 and Y1-2 are the lengths of the portions shown in FIG. 47(1).

[0087] Meanwhile, ray heights Y2-1 and Y2-2 are absolute values ​​of the ray heights of the chief ray at lens surface 3 adjacent to the reduction side of the second aperture stop and lens surface 4 adjacent to the magnification side. Specifically, in this example, as shown in FIG. 47(2), the lens surfaces on the second aperture stop AS2 side of lens L23 adjacent to the reduction side of second aperture stop AS2 and lens L24 adjacent to the magnification side of second aperture stop AS2 are lens surface 3 and lens surface 4, respectively. The chief ray at the extreme peripheral angle of view that emerges from lens surface 3 and enters lens surface 4 (which is assumed to be a surface perpendicular to the optical axis Z) is shown as a ray that forms an angle of incidence θ2 with lens surface 4. These ray heights Y2-1 and Y2-2 are the lengths of the portions shown in FIG. 47(2).

[0088] In this Example 1, the values ​​of the light ray heights Y1-1, Y1-2, Y2-1, and Y2-2 are as shown in Figure 42, and all satisfy equations (1), (2), (3), and (4), respectively. When the values ​​of Y1-1, Y1-2, Y2-1, and Y2-2 are large enough to satisfy equations (1) to (4), lenses L8 and L9 are sufficiently spaced from the first aperture stop AS1, and lenses L23 and L24 are sufficiently spaced from the second aperture stop AS2. Since the first aperture stop AS1 and the second aperture stop AS2 are prone to becoming hot due to exposure to light rays, if lenses L8, L9, L23, and L24 are sufficiently spaced from the aperture stop AS1 or AS2, respectively, it is possible to prevent lenses L8, L9, L23, and L24 from absorbing heat and becoming hot. Therefore, it is possible to prevent performance fluctuations of the imaging optical system 100 caused by heat absorption by these lenses L8, L9, L23, and L24. The detailed reason for this is as explained above.

[0089] The above-mentioned effects are more pronounced in the range defined by formula (1) if 2.0 < Y1-1 or 2.5 < Y1-1. The same is true if 2.0 < Y1-2 or 2.5 < Y1-2 is within the range defined by formula (2). The same is true if 1.5 < Y2-1 or 2.0 < Y2-1 is within the range defined by formula (3). The same is true if 1.0 < Y2-2 or 1.5 < Y2-2 is within the range defined by formula (4).

[0090] Next, Figure 42 shows the values ​​of Y1-1 / |fw|, Y1-2 / |fw|, Y2-1 / |fw|, and Y2-2 / |fw|, whose numerical ranges are defined by the above-mentioned formulas (5), (6), (7), and (8), respectively. These values ​​are obtained by dividing the above-mentioned four ray heights by the absolute value of fw, 9.08, and in this Example 1, all of these values ​​satisfy formulas (5), (6), (7), and (8), respectively. In this way, when formulas (5) to (8) are satisfied, the values ​​defined by formulas (1) to (4) are further divided by the focal lengths at the wide-angle end and the closest focusing distance, making it possible to accurately define the ray heights in the usage range where performance fluctuations are most likely to occur.

[0091] The above-described effects become more pronounced in the range defined by formula (5) if 0.6 < Y1-1 / |fw| and further if 0.7 < Y1-1 / |fw|. The same applies if 0.6 < Y1-2 / |fw| and further if 0.7 < Y1-2 / |fw| are within the range defined by formula (6). The same applies if 0.4 < Y2-1 / |fw| and further if 0.5 < Y2-1 / |fw| are within the range defined by formula (7). The same applies if 0.2 < Y2-2 / |fw| and further if 0.3 < Y2-2 / |fw| are within the range defined by formula (8).

[0092] FIG. 42 next shows the values ​​of distances D1-1, D1-2, D2-1, and D2-2 from the aperture to the lens surfaces, for which the numerical ranges of the aforementioned equations (9), (10), (11), and (12) are respectively defined. These distances will now be explained more clearly with reference to FIG. 47. Distances D1-2 and D1-2 are the distances between the first aperture and lens surface 1 adjacent to the reduction side of the first aperture and lens surface 2 adjacent to the magnification side of the first aperture. In this example, these lens surfaces 1 and 2 are specifically as shown in FIG. 47(1) as described above, and the distances D1-2 and D1-2 between the first aperture aperture AS1 and each of these lens surfaces 1 and 2 are also as shown in FIG. 47(1).

[0093] Meanwhile, distances D2-1 and D2-2 are the distances between the second aperture stop and lens surface 3 adjacent to the reduction side of the second aperture stop and lens surface 4 adjacent to the enlargement side of the second aperture stop. In this example, these lens surfaces 3 and 4 are specifically as shown in Figure 47(2) as described above, and the distances D2-1 and D2-2 between the second aperture stop AS2 and lens surface 3 and lens surface 4, respectively, are also as shown in Figure 47(2).

[0094] In this embodiment, the values ​​of the distances D1-1, D1-2, D2-1, and D2-2 from the aperture stop to the lens surface described above are as shown in FIG. 42, and all satisfy expressions (9), (10), (11), and (12), respectively. If lenses L8, L9, L23, and L24 are sufficiently far from aperture stop AS1 or AS2, respectively, to satisfy expressions (9) to (12), these lenses L8, L9, L23, and L24 can be prevented from absorbing heat and becoming too hot. Therefore, it is possible to prevent performance fluctuations of imaging optical system 100 due to heat absorption by these lenses L8, L9, L23, and L24.

[0095] Next, Figure 42 shows the values ​​of Ds1 and Ds2, whose magnitude relationship is defined by equation (13). As mentioned above, Ds1 = D1-1 + D1-2, and Ds2 = D2-1 + D2-2. Specifically, in this Example 1, Ds1 = 62.95 and Ds2 = 35.74, so the magnitude relationship defined by equation (13) is satisfied.

[0096] Figure 42 next shows the aperture diameter φs1 of aperture stop AS1, which is the first aperture, the aperture diameter φs2 of aperture stop AS2, which is the second aperture, the effective diameter φs1-1 of lens surface 1, the effective diameter φs1-2 of lens surface 2, the effective diameter φs2-1 of lens surface 3, and the effective diameter φs2-2 of lens surface 4, in that order.

[0097] 42 next shows the values ​​of φs1-1 / φs1, φs1-2 / φs1, φs2-1 / φs2, and φs2-2 / φs2, which are derived from the values ​​of the effective diameters described above. The numerical ranges of the value of φs1-1 / φs1 are defined by the above-mentioned formula (19), the value of φs1-2 / φs1 by formula (20), the value of φs2-1 / φs2 by formula (21), and the value of φs2-2 / φs2 by formula (22). In this Example 1, these values ​​are 1.42, 1.25, 1.58, and 1.00, respectively, and therefore all of formulas (19), (20), (21), and (22) are satisfied.

[0098] Equations (19) and (20) define the effective diameters of the reduction-side lens surface and the magnification-side lens surface of the adjacent lens relative to the aperture diameter of the first aperture. These definitions make it possible to limit the degree of focusing of light rays on the lens surface. If the defined values ​​are below the lower limit of each equation, the focusing of light rays on the lens surface will be too intense, and the lens glass material will be affected by the light energy, resulting in changes in optical performance. Conversely, if the defined values ​​are above the upper limit of each equation, the effective diameter of the lens will become too large, resulting in an increase in the overall size of the optical system. Satisfying equations (19) and (20) prevents such problems from occurring.

[0099] Formulas (21) and (22) define the effective diameters of the reduction-side lens surface and the enlargement-side lens surface of the adjacent lens relative to the aperture diameter of the second diaphragm. In this case, too, if formulas (21) and (22) are satisfied, the same effect as when formulas (19) and (20) are satisfied can be obtained.

[0100] Next, Figure 42 shows the angle of incidence θ1 of the chief ray at the most peripheral angle of view onto the first diaphragm (aperture diaphragm AS1), and the angle of incidence θ2 of the chief ray at the most peripheral angle of view onto the second diaphragm (aperture diaphragm AS2). Note that the units of the angles of incidence θ1 and θ2 shown here are degrees. Below that, the tangent values ​​tanθ1 and tanθ2 of the angles of incidence θ1 and θ2, respectively, are shown. These values ​​of tanθ1 and tanθ2 are, of course, absolute numbers.

[0101] Next, Figure 42 shows values ​​related to the above tan θ1 and tan θ2 values, including the value of tan θ2 / tan θ1, whose numerical range is defined by the above formula (16), the value of tan θ1 × |fw|, whose numerical range is defined by the above formula (14), and the value of tan θ2 × |fw|, whose numerical range is defined by the above formula (15). As mentioned above, |fw| = 9.08. In this Example 1, specifically, tan θ2 / tan θ1 = 1.90, which satisfies formula (16). Furthermore, tan θ1 × |fw| = 2.35, which satisfies formula (14). Furthermore, tan θ2 × |fw| = 4.45, which satisfies formula (15).

[0102] If expressions (14) and (15) are satisfied as described above, the overall lens length can be prevented from increasing, which is advantageous for reducing the size of the imaging optical system 100. The detailed reasons for this are as described above. In particular, in this first embodiment, the more preferable relationship of 1.5 < tan θ1 × |fw| < 2.5 is also satisfied within the range defined by expression (14), and the more preferable relationship of 3.0 < tan θ2 × |fw| < 5.5 is also satisfied within the range defined by expression (15), making the above effect even more pronounced. Furthermore, since expression (16) is satisfied, it is possible to prevent the overall length of the first refractive system R1 or the second refractive system R2 from increasing and the cost of the imaging optical system 100 from increasing. The detailed reasons for this are as described above.

[0103] FIG. 42 also shows the value of Ds1 × tan θ1, which is related to the values ​​of DS1 and tan θ1 and whose numerical range is defined by the above-mentioned formula (17). In the first embodiment, specifically, Ds1 × tan θ1 = 16.28, which satisfies formula (17). Satisfying formula (17) can prevent problems such as a reduction in the ray height defined by formula (1), which would have an adverse effect on the optical performance of the imaging optical system 100, making it difficult to miniaturize the imaging optical system 100, and reducing the peripheral illumination ratio. The detailed reasons for this are as described above. In particular, in the first embodiment, the more preferable relationship of 7.0 < Ds1 × tan θ1 < 18.0 is also satisfied within the range defined by formula (17), making the above-mentioned effect even more pronounced.

[0104] Next, FIG. 42 shows the value of Ds2 × tan θ2, which is related to the values ​​of Ds2 and tan θ2 and for which the numerical range is defined by the above formula (18). In this Example 1, specifically, Ds2 × tan θ2 = 11.77, which satisfies formula (18). If formula (18) is satisfied, the same effect as when formula (17) is satisfied can be obtained. The detailed reason for this is as described above. In particular, in this Example 1, the more preferable relationship of 10.0 < Ds2 × tan θ2 < 25.0 is also satisfied within the range defined by formula (18), so the above effect is even more pronounced.

[0105] Next, Figure 42 shows the value of Y2-2 × tan θ2, which is related to the values ​​of Y2-2 and tan θ2 and for which the numerical range is defined by the above formula (23). In this Example 1, specifically, Y2-2 × tan θ2 = 1.20, which satisfies formula (23). If formula (23) is satisfied, it is possible to reduce the load of light rays on the lenses near the aperture stop AS2. The detailed reason for this is as explained above.

[0106] Next, Figure 42 shows the value of D2-2 / Y2-2, which is related to the values ​​of D2-2 and Y2-2 and whose numerical range is defined by the above formula (24). In this Example 1, specifically, D2-2 / Y2-2=2.04, which satisfies formula (24). If formula (24) is satisfied, it is possible to reduce the load of light rays on the lenses near the aperture stop AS2. The detailed reason for this is as explained above.

[0107] 43 to 45, the characteristics of the lenses near the first and second apertures, i.e., the first adjacent lenses located adjacent to the reduction and enlargement sides of each aperture, respectively, and the second adjacent lenses located adjacent to the first adjacent lenses on the opposite side of the apertures, will be described. In this example, the first aperture is aperture aperture AS1, and the second aperture is aperture aperture AS2. A set of the first adjacent lens and the second adjacent lens is referred to as a group, with the groups on the reduction and enlargement sides of aperture aperture AS1 being group 1 and group 2, respectively, and the groups on the reduction and enlargement sides of aperture aperture AS2 being group 3 and group 4, respectively. As can be seen from FIG. 1 and other figures, specifically, in group 1, lenses L7 and L8 are the second adjacent lens and the first adjacent lens, respectively. In group 2, lenses L9 and L10 are the first adjacent lens and the second adjacent lens, respectively. On the other hand, in group 3, lenses L22 and L23 are the second adjacent lens and the first adjacent lens. In group 4, lenses L24 and L25 are the first adjacent lens and the second adjacent lens, respectively.

[0108] FIG. 43 shows the glass materials of the first adjacent lenses and the second adjacent lenses in the above-mentioned groups 1 to 4 together for each example.

[0109] FIG. 44 shows the internal transmittance τ420 values ​​mentioned above for each of the above glass materials. This value is an absolute number, and if expressed as a percentage, for example, 0.991 is 99.1%. Below, with reference to FIG. 44, the configuration related to the above-mentioned formulas (25) to (27) will be explained. First, among the lenses included in groups 1 to 4, the lenses with Abbe numbers at the d-line of less than 40 are the first adjacent lens in group 2 (lens L9), the second adjacent lens in group 3 (lens L22), and the second adjacent lens in group 4 (lens L25). In other words, the Abbe numbers νd of these lenses are 32.3, 35.0, and 35.2, respectively (see FIG. 5, and the same applies below), and their τ420 are 0.982, 0.901, and 0.931, respectively, thereby satisfying the above-mentioned formula (25).

[0110] On the other hand, of the lenses included in groups 1 to 4, the lenses whose Abbe numbers at the d-line are 40 or more are the first adjacent lens (lens L7) and second adjacent lens (lens L8) in group 1, the second adjacent lens (lens L10) in group 2, the first adjacent lens (lens L23) in group 3, and the first adjacent lens (lens L24) in group 4. In other words, the Abbe numbers νd of these lenses are 54.7, 69.9, 44.3, 70.2, and 70.2, respectively, and their τ420 are 0.991, 0.995, 0.989, 0.999, and 0.999, respectively, which satisfy the above-mentioned formula (26) and also satisfy formula (27).

[0111] As described above, if expressions (25) and (26) are satisfied, it is possible to design a lens configuration that has the necessary aberration correction capabilities while suppressing the absorption of light on the short wavelength side, such as blue light, in lenses L8, L9, and L10 that are close to aperture stop AS1. The detailed reasons for this are as explained above.

[0112] Next, let us consider the configuration related to equation (28). The first adjacent lenses or second adjacent lenses related to these equations, that is, the eight lenses L7 to L10 and L22 to L25 included in groups 1 to 4, all have |dn / dt| < 6.5 as shown in FIG. 45, and therefore satisfy equation (28). This makes it possible to suppress the impact of heat on the optical performance of these lenses. The detailed reasons for this are as explained above.

[0113] Next, with reference to FIG. 46, the configuration related to the above-mentioned formulas (29) to (30) will be described. FIG. 46 summarizes the anomalous dispersion θg,F of the main lenses for each embodiment. In this embodiment 1, two lenses, lenses L3 and L4, are listed as positive lenses arranged on the reduction side of the aperture stop AS1, which is the first stop. The anomalous dispersion θg,F of the glass materials of these lenses L3 and L4 are 0.0457 and 0.0276, respectively, both of which exceed 0.005. Furthermore, the Abbe numbers νd at the d line (587.6 nm) of the glass materials of these lenses L3 and L4 are 94.7 and 75.5, respectively (see FIG. 5; the same applies below), both of which exceed 65. Therefore, in this embodiment 1, formula (29) is satisfied.

[0114] In this Example 1, five lenses, L12, L15, L17, L26, and L27, are listed in FIG. 46 as positive lenses located on the magnification side of the aperture stop AS1, which is the first stop. The anomalous dispersions θg,F of the glass materials of these lenses L12, L15, L17, L26, and L27 are 0.0457, 0.0457, 0.0457, and 0.0123, respectively, all of which exceed 0.005. The Abbe numbers νd at the d-line (587.6 nm) of the glass materials of these lenses L12, L15, L17, L26, and L27 are 94.7, 94.7, 94.7, and 67.7, respectively, all of which exceed 65. Therefore, in this Example 1, formula (30) is satisfied.

[0115] As described above, by satisfying the formulas (29) and (30), it becomes possible to appropriately correct insufficient chromatic aberration while using a glass material with a high Abbe number νd.

[0116] In this first embodiment, as described above, expressions (1) to (4) are satisfied and the angles of incidence of light rays to aperture stop AS1, which is the first stop, and aperture stop AS2, which is the second stop, are appropriately set, so that a long overall length of first refractive system R1 can be ensured. In the space created thereby within first refractive system R1, zoom groups z1 to z5 or zoom groups z1 to z6 can be appropriately arranged as shown in FIGS. 3 and 4, making it possible to realize a zoom lens with high-quality optical performance.

[0117] Furthermore, in this embodiment 1, lens L1 is arranged at the most reduction side of the imaging optical system 100 as a fixed group 1 having a positive focal length that does not move during zooming, making it easy to make the imaging state on the reduction side of the imaging optical system 100 telecentric at both the wide-angle end and the telephoto end.

[0118] If the fixed group 1 is made up of a single positive lens, various aberrations will be large, so it is more preferable that the fixed group 1 be made up of a plurality of lenses, and it is even more preferable that it include a negative lens.

[0119] Furthermore, in this first embodiment, the zoom group z2, which has the maximum number of lenses (five lenses) and is arranged on the reduction side of the aperture stop AS1, which is the first stop, has the effect of determining the zoom ratio (variable magnification), and because this zoom group z2 has a positive focal length, it is preferable in terms of shortening the movement distance associated with variable magnification.

[0120] The zoom group z3 located adjacent to the zoom group z2 on the magnification side also has a positive focal length, which is advantageous in terms of reducing costs by reducing the diameters of the lens groups that follow it on the magnification side and the aspherical lenses contained therein. Furthermore, the zoom group z3 is made up of a positive meniscus lens that is convex toward the magnification side, which is also advantageous in terms of reducing aberrations.

[0121] In order to maintain a long object distance (back focus) on the reduction side, it is preferable that the first refractive system R1 be a retrofocus type. Furthermore, it is preferable that the rear group of the first refractive system R1, i.e., the lens group on the reduction side of the aperture stop AS1 (the first stop), be a positive lens group, and the front group, i.e., the lens group on the enlargement side of the aperture stop AS1 be a negative lens group. Therefore, it is preferable that the zoom group z5 or z6 (see Figures 3 and 4) on the most enlargement side have a negative focal length.

[0122] It is preferable that the magnification side of the front group of the first refractive system R1 includes a negative meniscus aspherical lens that generates significant coma aberration to compensate for the coma aberration generated by the second refractive system R1. In this embodiment, lens L16 is such a negative meniscus aspherical lens. In this embodiment, the group closest to the magnification side of the front group is made up of lenses L18 and L19, and this group is a fixed group that does not move during magnification. Such a fixed group can be used as a measurement standard for decentering and the like during the manufacture of the imaging optical system 100, and is therefore a preferable configuration.

[0123] The first optical system OP1 includes an aperture unit consisting of a first field aperture FS1, a first aperture aperture AS1, and a second field aperture FS2, but in the zoom group configuration of Figure 4, this aperture unit is located outside the first zoom group (the zoom group with the largest number of lenses: zoom group z2 in this example) and is configured to move integrally with zoom group z2. Apertures such as the first aperture aperture AS1 are heated by the light they cut, but the configuration described above makes it possible to prevent the heat from the apertures from being transferred to the lenses in zoom group z2 and impairing optical performance.

[0124] In this first embodiment, several lens groups on the reduction side of the first aperture stop AS1 are moved to vary the magnification. In doing so, it is desirable to design the system so that the height of the axial marginal ray does not vary between the wide-angle and telephoto sides. This results in an imaging optical system 100 in which the F-number does not vary between the wide-angle and telephoto sides, making it possible to achieve a desirable usage state.

[0125] Furthermore, the lenses L2, L11, L16, and L19 included in the first refractive system R1 are negative meniscus lenses, and it is preferable that these negative meniscus lenses have a large thickness ratio between the center and periphery of the lens in order to reduce inter-surface reflection ghosts caused by high-brightness light.

[0126] In this first embodiment, a portion of the focus group f2 and the focus group f3 are disposed in the second refractive system R2. Because the amount of movement of the focus group is small compared to the zoom group, it is preferable to dispose them in the second refractive system R2 in this manner. Furthermore, since the focus group is resistant to distance fluctuations in an ultra-single focus lens, it is preferable that the focus group be a floating focus lens in which multiple groups are moved. It is preferable to dispose one group of the floating focus lens, for example, the focus group f1, in a portion of the first refractive system R1, which does not move during zooming, because this simplifies the mechanical structure and saves space for movement.

[0127] It is preferable that one of the focus groups be a group that sandwiches the intermediate image Im1, like the focus group f2 in this first embodiment. The intermediate image Im1 is an image point, and if dust or the like adheres to a lens surface near this image point, it will have an effect such as casting a shadow on the image. For this reason, integrating the focus groups that sandwich the intermediate image Im1 into one unit makes it possible to keep the interior clean when assembled, which is preferable. In the focus group f2 that sandwiches the intermediate image Im1, it is preferable to arrange positive meniscus lenses L18 and L20 facing each other to complement aberrations, and it is also preferable to arrange a negative lens L19 to further reduce aberrations.

[0128] The group on the most magnification side of the second refractive system R2 is preferably a fixed group consisting of lenses L24 to L27, since it has a high sensitivity to decentration relative to the concave mirror 6. From this perspective, it is also preferable that the focus group f3 on the most magnification side be located adjacent to the reduction side of the second aperture stop AS2, which is the second stop. Furthermore, the focus group f3 on the most magnification side needs to be a positive group because it is required to have an imaging function. Therefore, the focus group f3 needs to be configured using a positive single lens, or multiple positive lenses L21 and L23 as in the first embodiment. Furthermore, it is preferable that the focus group f3 have a positive-negative-positive configuration, including a negative lens L22, to reduce aberrations during focusing.

[0129] On the other hand, it is preferable to include an offset prism 5 between the second refractive system R2 and the second optical system OP2 to shift the optical axis. This makes it possible to bring the projection screen closer to the lens. The prism 5 has two reflective surfaces, and it is preferable to determine the inclination angles of the reflective surfaces so that all luminous flux is totally reflected, as this increases the light transmission efficiency.

[0130] Next, aberrations in the imaging optical system 100 of Example 1 will be described. FIG. 9 shows the longitudinal aberration of the imaging optical system 100 of Example 1. (1) and (2) of FIG. 9 show the results of measuring the transverse aberration when the imaging optical system 100 is at the wide-angle end and the telephoto end, respectively (units are mm). Each figure shows, from left to right, the spherical aberration, astigmatism, and distortion of the imaging optical system 100 of Example 1. Spherical aberration calculations were performed for light with wavelengths of 620.00 nm, 550.00 nm, and 450.00 nm, and the measurement results for each wavelength are distinguished by different line types on the graphs. Astigmatism was measured for light with a wavelength of 550.00 nm in the tangential and sagittal planes. The former is indicated by a T and the latter by an S. Distortion calculations were performed for light with a wavelength of 550.00 nm. As can be seen, spherical aberration, astigmatism, and distortion are well corrected.

[0131] 10 and 11 show the lateral aberration of the imaging optical system 100 of Example 1, respectively. These Figures 10 and 11 show the results of measuring the lateral aberration when the imaging optical system 100 is at the wide-angle end and the telephoto end, respectively (units: mm). In each case, the image was projected in focus at the closest point, and the lateral aberration was measured in the tangential direction (Y-FAN) and the sagittal direction (X-FAN) at five points on the projection screen. These five points include one point with the maximum relative field height (this is assumed to be a relative field height of 1.00) and four points with relative field heights (in Example 1, 0.79, 0.53, 0.26, and 0.16), for a total of five points. The measurement results at these points are shown from top to bottom in the figures. The maximum field height (maximum image height) for each example is 19.5 mm for Example 1, 19.5 mm for Example 2, 19.5 mm for Example 3, 11.2 mm for Example 4, and 22.0 mm for Example 5. Because lateral aberration in the sagittal direction is symmetrical about the center, only one side of the sagittal direction is shown. The lateral aberration measurements were performed for light with wavelengths of 620.0 nm, 550.0 nm, and 460.0 nm, and the measurement results for each wavelength are distinguished by different line styles on the graphs. As shown in Figures 10 and 11, lateral aberration is effectively suppressed both when the imaging optical system 100 is at the wide-angle end and the telephoto end.

[0132] Next, Example 2 according to another embodiment of the present invention will be described. FIG. 12 is a cross-sectional view showing the configuration of an imaging optical system 200 according to Example 2 of the present invention, along with the main light beams. FIG. 12 shows the imaging optical system 200 at the wide-angle end, and FIG. 13 shows the imaging optical system 200 at the wide-angle end, excluding the light beams. In FIGS. 12 and 13, elements equivalent to those in FIGS. 1 to 4 described above are denoted by the same numbers, and their description will be omitted unless otherwise necessary (the same applies hereinafter). The notation in FIGS. 12 and 13 is the same as in FIGS. 18 and 19, which will be described later.

[0133] This imaging optical system 200 is also applied to a projection device that enlarges and projects an image displayed on an image display surface 1, and is basically composed of a first optical system OP1 and a second optical system OP2 arranged on the enlargement side of the first optical system OP1. The first optical system OP1 is composed of a first refractive system R1 and a second refractive system R2. Below, the elements such as lenses that compose the first refractive system R1 and the second refractive system R2 in this Example 2 will be specifically described. The first refractive system R1 is configured by sequentially arranging, from the reduction side to the enlargement side along the optical axis Z, a biconvex lens L1, a biconvex lens L2, a negative meniscus lens L3, a negative meniscus lens L4, a biconvex lens L5, a negative meniscus lens L6, a positive meniscus lens L7, a negative meniscus lens L8, a biconvex lens L9, a first field stop FS1, a first aperture stop AS1, a second field stop FS2, a biconvex lens L10, a negative meniscus lens L11, a biconvex lens L12, a biconcave lens L13, a biconvex lens L14, a negative meniscus lens L15, a positive meniscus lens L16, a positive meniscus lens L17, and a negative meniscus lens L18. A first intermediate image Im1 is formed by the first refractive system R1.

[0134] On the other hand, the second refractive system R2 is composed of a positive meniscus lens L19, a biconvex lens L20, a second aperture stop AS2, a biconvex lens L21, a negative meniscus lens L22, a biconvex lens L23, and a biconvex lens L24 arranged in this order from the reduction side to the enlargement side along the optical axis Z. The first intermediate image Im1 is further formed as a second intermediate image Im2 by the second refractive system R2. The second intermediate image Im2 is reflected and enlarged by the second optical system OP2 and projected as an enlarged image onto a screen (not shown).

[0135] Detailed data of the components in this Example 2 is shown in Fig. 14. Also, aspherical data regarding the aspherical surfaces in these components is shown in Fig. 15. In this Example 2, the aspherical shapes of all aspherical surfaces are expressed by the following equations using the aspherical coefficients shown in Fig. 15. X=(1 / Rdy)R 2 / [1+{1-(1+K)(1 / Rdy) 2 R 2}1 / 2 ] +A3R 3 +A4R 4 +A6R 6 +A8R 8 +A10R 10 +A12R 12

[0136] In the second embodiment and the third embodiment described below, the configurations of the zoom group and the focus group will not be described in detail, but conventionally known configurations can be appropriately adopted.

[0137] Similar to the case of the above-described Example 1, a more detailed configuration of Example 2 is shown in Figure 42. Furthermore, as data on lenses near the aperture stop in Example 2, data on the first and second adjacent lenses of groups 1 and 2 relative to aperture stop AS1, and the first and second adjacent lenses of groups 3 and 4 relative to aperture stop AS2 are shown in Figures 43, 44, and 45. In Example 2, the second adjacent lens and first adjacent lens of group 1, the first adjacent lens and second adjacent lens of group 2, the second adjacent lens and first adjacent lens of group 3, and the first adjacent lens and second adjacent lens of group 4 are specifically shown in order from the reduction side to the enlargement side as lenses L8, L9, L10, L11, L19, L20, L21, and L23, respectively. Fig. 43 shows the glass materials of the above lenses, Fig. 44 shows the values ​​of the internal transmittance τ420 of those glass materials, and Fig. 45 shows the relative temperature coefficients of refractive index dn / dt of those glass materials. As shown in Fig. 44 and Fig. 45, all of the lenses included in groups 1 to 4 of Example 2 satisfy formula (25) or formula (26), and also satisfy formula (28).

[0138] Figure 46 also shows the anomalous dispersion θg,F of the main lenses in Example 2. In Example 2, two lenses, lenses L2 and L5, are listed as positive lenses arranged on the reduction side of aperture stop AS1, which is the first stop, and five lenses, lenses L14, L16, L17, L23, and L24, are listed as positive lenses arranged on the enlargement side of aperture stop AS1, and the anomalous dispersion θg,F of these lenses is shown. As shown in Figure 46, the imaging optical system 200 of Example 2 satisfies formulas (29) and (30).

[0139] Next, aberrations in the imaging optical system 200 of this second embodiment will be described. Fig. 16 shows the lateral aberrations when the imaging optical system 200 of this second embodiment is at the wide-angle end. The way in which the lateral aberrations are displayed in Fig. 16 is the same as the way in which they are displayed in Figs. 10 and 11 described above. As shown in Fig. 16, the lateral aberrations are also well suppressed in this second embodiment.

[0140] 17 shows, from left to right, the spherical aberration, astigmatism, and distortion in the imaging optical system 200 of this Example 2. As shown here, the spherical aberration, astigmatism, distortion, and lateral aberration are well corrected.

[0141] Next, Example 3 according to another embodiment of the present invention will be described. Fig. 18 is a cross-sectional view showing the configuration of an imaging optical system 300 according to Example 3 of the present invention, along with the main light beams. Fig. 18 shows the imaging optical system 300 at the wide-angle end, and Fig. 19 shows the imaging optical system 300 at the wide-angle end, excluding the light beams.

[0142] This imaging optical system 300 is also applied to a projection device that enlarges and projects an image displayed on an image display surface 1, and is basically composed of a first optical system OP1 and a second optical system OP2 arranged on the enlargement side of the first optical system OP1. The first optical system OP1 is composed of a first refractive system R1 and a second refractive system R2. Below, the elements such as lenses that compose the first refractive system R1 and the second refractive system R2 in this Example 3 will be specifically described. The first refractive system R1 is configured by sequentially arranging, from the reduction side to the enlargement side along the optical axis Z, a biconvex lens L1, a biconvex lens L2, a negative meniscus lens L3, a negative meniscus lens L4, a biconvex lens L5, a negative meniscus lens L6, a positive meniscus lens L7, a negative meniscus lens L8, a biconvex lens L9, a first field stop FS1, a first aperture stop AS1, a second field stop FS2, a biconvex lens L10, a negative meniscus lens L11, a biconvex lens L12, a biconcave lens L13, a biconvex lens L14, a negative meniscus lens L15, a positive meniscus lens L16, a positive meniscus lens L17, and a negative meniscus lens L18. A first intermediate image Im1 is formed by the first refractive system R1.

[0143] On the other hand, the second refractive system R2 is composed of a positive meniscus lens L19, a biconvex lens L20, a second aperture stop AS2, a biconvex lens L21, a negative meniscus lens L22, a biconvex lens L23, and a biconvex lens L24 arranged in this order from the reduction side to the enlargement side along the optical axis Z. The first intermediate image Im1 is further formed as a second intermediate image Im2 by the second refractive system R2. The second intermediate image Im2 is reflected and enlarged by the second optical system OP2 and projected as an enlarged image onto a screen (not shown).

[0144] Detailed data of the components in this Example 3 is shown in Fig. 20. Aspherical data regarding the aspherical surfaces in these components is shown in Fig. 21. In this Example 3, the aspherical shapes of all aspherical surfaces are expressed by the following equations using the aspherical coefficients shown in Fig. 21. X=(1 / Rdy)R 2 / [1+{1-(1+K)(1 / Rdy) 2 R 2}1 / 2 ] +A3R 3 +A4R 4 +A6R 6 +A8R 8 +A10R 10 +A12R 12

[0145] Similar to the case of the above-described Example 1, a more detailed configuration of Example 3 is shown in Figure 42. Furthermore, as data on lenses near the aperture stop in Example 3, data on the first and second adjacent lenses of groups 1 and 2 relative to aperture stop AS1, and the first and second adjacent lenses of groups 3 and 4 relative to aperture stop AS2 are shown in Figures 43, 44, and 45. In Example 3, the second adjacent lens and first adjacent lens of group 1, the first adjacent lens and second adjacent lens of group 2, the second adjacent lens and first adjacent lens of group 3, and the first adjacent lens and second adjacent lens of group 4 are specifically shown in order from the reduction side to the enlargement side as lenses L8, L9, L10, L11, L19, L20, L21, and L23, respectively. Fig. 43 shows the glass materials of the above lenses, Fig. 44 shows the values ​​of the internal transmittance τ420 of those glass materials, and Fig. 45 shows the relative temperature coefficients of refractive index dn / dt of those glass materials. As shown in Fig. 44 and Fig. 45, all of the lenses included in groups 1 to 4 of Example 3 satisfy formula (25) or formula (26), and also satisfy formula (28).

[0146] Figure 46 also shows the anomalous dispersion θg,F of the main lenses in Example 3. In Example 3, two lenses, lenses L2 and L5, are listed as positive lenses arranged on the reduction side of aperture stop AS1, which is the first stop, and four lenses, lenses L14, L16, L23, and L24, are listed as positive lenses arranged on the enlargement side of aperture stop AS1, and the anomalous dispersion θg,F of these lenses is shown. As shown in Figure 46, the imaging optical system 300 of Example 3 satisfies formulas (29) and (30).

[0147] Next, aberrations in the imaging optical system 300 of this Example 3 will be described. Fig. 22 shows the lateral aberrations when the imaging optical system 300 of this Example 3 is at the wide-angle end. The way in which the lateral aberrations are displayed in Fig. 22 is the same as the way in which they are displayed in Figs. 10 and 11 described above. As shown in Fig. 22, the lateral aberrations are also well suppressed in this Example 3.

[0148] 23 shows, from left to right, the spherical aberration, astigmatism, and distortion in the imaging optical system 300 of this Example 3. The method of measuring and displaying these aberrations is the same as in the previously described Example 2. As shown here, the spherical aberration, astigmatism, and distortion are also well corrected in this Example 3.

[0149] Next, a fourth embodiment of the present invention will be described. FIG. 24 is a cross-sectional view showing the configuration of an imaging optical system 400 according to the fourth embodiment of the present invention, along with the main light beams. In FIG. 24, the upper part shows the imaging optical system 400 at the wide-angle end, and the lower part shows the imaging optical system 400 at the telephoto end. FIG. 25 also shows the zoom groups z1 to z4 and the focus groups f1 to f4 when the imaging optical system 400 is at the wide-angle end. The imaging optical system 400 of the fourth embodiment is not applied to a projection device that uses the concave mirror 6 described above to reflect a light beam, but rather to a projection device that projects a light beam emitted from the magnification side, i.e., the second refractive system R2 side, onto a screen or the like without being reflected along the way. This is also true for the imaging optical system 500 of the fifth embodiment, which will be described later.

[0150] For convenience of illustration, in FIGS. 24 and 25, the reduction side is shown on the right and the magnification side is shown on the left, which is the opposite of Examples 1 to 3. The names of the lenses L1, L2, etc., and the names of the focus groups f1 to f4 and zoom groups z1 to z4 in FIG. 25 are numbered in increasing order from the magnification side to the reduction side. However, the names of the aperture stops AS1 to AS2 and field stops FS1 to FS4, which are related to the core of the present invention, are numbered in increasing order from the reduction side to the magnification side. That is, with regard to aperture stops AS1 and AS2, the one on the reduction side is referred to as the first stop (first aperture stop AS1), and the one on the magnification side is referred to as the second stop (second aperture stop AS2). The notational methods in FIGS. 24 and 25 described above are also used in FIGS. 33 and 34, which show the imaging optical system 500 of Example 5.

[0151] Similar to the imaging optical system 500 described later, this imaging optical system 400 is composed of a first optical system OP1 for forming an image formed on an image display element 12 formed on the reduction-side end face of a color synthesis prism 11, such as a dichroic prism or a TIR prism, onto the screen or the like. The first optical system OP1 is composed of a first refractive system R1 and a second refractive system R2. The elements such as lenses constituting the first refractive system R1 and the second refractive system R2 in this fourth embodiment will be described below.

[0152] As shown in Figures 24 and 25, the first refractive system R1 is composed of a biconvex lens L26, a positive meniscus lens L25, a negative meniscus lens L24, a biconvex lens L23, a biconcave lens L22, a biconvex lens L21, a negative meniscus lens L20, a negative meniscus lens L19, a positive meniscus lens L18, a first field stop FS1, a first aperture stop AS1, a second field stop FS2, a biconvex lens L17, a negative meniscus lens L16, a biconvex lens L15, a biconcave lens L14, a negative meniscus lens L13, a biconcave lens L12, and a biconvex lens L11 arranged in sequence along the optical axis Z from the reduction side to the enlargement side.

[0153] The second refractive system R2 is arranged on the magnification side across the intermediate image Im formed by the first refractive system R2 and is composed of a biconvex lens L10, a negative meniscus lens L9, a biconvex lens L8, a negative meniscus lens L7, a biconvex lens L6, a biconvex lens L5, a third field stop FS3, a second aperture stop AS2, a fourth field stop FS4, a biconvex lens L4, a biconcave lens L3, a negative meniscus lens L2, and a negative meniscus lens L1, arranged in this order from the reduction side to the magnification side along the optical axis Z. The second refractive system R2 further forms the intermediate image Im on a screen or the like (not shown).

[0154] Detailed data of the components in this Example 4 is shown in Fig. 26. The display method in Fig. 26 is basically the same as that in Figs. 5, 14, and 20, but in Fig. 26, "Im," "PR11," and "IS12" respectively indicate the intermediate image Im, the prism 11, and the image display element 12. Fig. 27 shows aspheric data related to the aspheric surfaces in these components. In this Example 4, the aspheric shapes of all aspheric surfaces are expressed by the following equations using the aspheric coefficients shown in Fig. 27. X=(1 / Rdy)R 2 / [1+{1-(1+K)(1 / Rdy) 2 R 2} 1 / 2 ] +A4R 4 +A6R 6 +A8R 8 +A10R 10 +A12R 12 +A14R 14 +A16R 16

[0155] Next, the movement amounts of the zoom group and the focus group will be described with reference to FIG. 28. In FIG. 28, the "s + numerical value" column shows the surface spacing (unit: mm) of the surfaces shown in FIG. 26, and the numerical value indicates the surface number (No.). For example, s2 indicates the surface spacing of the surface with surface number 2, i.e., the lens surface on the reduction side of lens L1, relative to the next surface with number 3. The "ZOOM" notation below each "s + numerical value" column indicates that the surface spacing of that displayed column changes with zooming, and the "FOCUS" notation indicates that the surface spacing of that displayed column changes with focusing. The "Z" column shows six different states of the lens group depending on zooming or focusing. States 1 to 3 indicate states where the lens is focused on the closest screen or the like that can be focused on, and states 4 to 6 indicate states where the lens is focused on the farthest screen or the like that can be focused on. Moreover, states 1 and 4 are wide-angle end states set by zooming, states 2 and 5 are intermediate states between the wide-angle end and the telephoto end, and states 3 and 6 are telephoto end states.

[0156] Similar to the case of the above-described Example 1, a more detailed configuration of Example 4 is shown in Figure 42. Furthermore, as data on lenses near the aperture stop in Example 4, data on the first and second adjacent lenses of groups 1 and 2 relative to aperture stop AS1, and the first and second adjacent lenses of groups 3 and 4 relative to aperture stop AS2 are shown in Figures 43, 44, and 45. In Example 4, the second adjacent lens and first adjacent lens of group 1, the first adjacent lens and second adjacent lens of group 2, the second adjacent lens and first adjacent lens of group 3, and the first adjacent lens and second adjacent lens of group 4 are specifically shown in order from the reduction side to the enlargement side as lenses L19, L18, L17, L16, L6, L5, L4, and L3, respectively.

[0157] That is, the data shown in Fig. 42 are for a configuration in which lenses L7, L8, L9, and L10 in the diagram shown in Fig. 47(1) are lenses L19, L18, L17, and L16, respectively, of Example 4, and lenses L22, L23, L24, and L25 in the diagram shown in Fig. 47(2) are lenses L6, L5, L4, and L3, respectively, of Example 4. Fig. 43 shows the glass materials of lenses L19 and L18 as the second and first adjacent lenses in group 1, lenses L17 and L16 as the first and second adjacent lenses in group 2, lenses L6 and L5 as the second and first adjacent lenses in group 3, and lenses L4 and L3 as the first and second adjacent lenses in group 4 in Example 4, Fig. 44 shows the values ​​of internal transmittance τ420 of those glass materials, and Fig. 45 shows the relative temperature coefficients dn / dt of the refractive index of those glass materials. As shown in FIGS. 44 and 45, all of the lenses included in groups 1 to 4 in this fourth embodiment satisfy either formula (25) or formula (26), and also satisfy formula (28).

[0158] Figure 46 also shows the anomalous dispersion θg,F of the main lenses in Example 4. In Example 4, four lenses, L26, L25, L23, and L21, are listed as positive lenses arranged on the reduction side of aperture stop AS1, which is the first stop, and two lenses, L11 and L10, are listed as positive lenses arranged on the enlargement side of aperture stop AS1, and the anomalous dispersion θg,F of these lenses is shown. As shown in Figure 46, the imaging optical system 400 of Example 4 satisfies formulas (29) and (30).

[0159] Next, aberrations in the imaging optical system 400 of this fourth embodiment will be described. Fig. 29 shows, from left to right, spherical aberration, astigmatism, and distortion when the imaging optical system 400 of this fourth embodiment is at the wide-angle end. Fig. 30 shows lateral aberration when the imaging optical system 400 is at the wide-angle end. As shown in Figs. 29 and 30, spherical aberration, astigmatism, distortion, and lateral aberration are well corrected.

[0160] Furthermore, Fig. 31 shows, from left to right, the spherical aberration, astigmatism, and distortion when the imaging optical system 400 of this Example 4 is at the telephoto end. Fig. 32 shows the lateral aberration when the imaging optical system 400 is at the telephoto end. As shown in Figs. 31 and 32, the spherical aberration, astigmatism, distortion, and lateral aberration are well corrected.

[0161] Next, Example 5 according to another embodiment of the present invention will be described. Fig. 33 is a cross-sectional view showing the configuration of an imaging optical system 500 according to Example 5 of the present invention, along with main light beams. In Fig. 33, the upper part shows the imaging optical system 500 at the wide-angle end, and the lower part shows the imaging optical system 500 at the telephoto end. Fig. 34 also shows zoom groups z1 to z4 and focus groups f1 to f3 when the imaging optical system 500 is at the wide-angle end.

[0162] This imaging optical system 500 is also applied to a projection device that forms and projects an image on a screen or the like without reflecting the light beam emitted from the second refraction system R2, and is basically composed of a first optical system OP1 for the above-mentioned imaging. This first optical system OP1 is composed of a first refraction system R1 and a second refraction system R2. Hereinafter, elements such as lenses that constitute the first refraction system R1 and the second refraction system R2 in this embodiment 5 will be described.

[0163] As shown in Figures 33 and 34, the first refractive system R1 is composed of a biconvex lens L23, a positive meniscus lens L22, a negative meniscus lens L21, a biconvex lens L20, a biconcave lens L19, a biconvex lens L18, a negative meniscus lens L17, a first field stop FS1, a first aperture stop AS1, a second field stop FS2, a biconvex lens L16, a third field stop FS3, a biconvex lens L15, a biconvex lens L14, a biconcave lens L13, a negative meniscus lens L12, a biconcave lens L11, and a positive meniscus lens L10 arranged in sequence along the optical axis Z from the reduction side to the enlargement side.

[0164] The second refraction system R2, located on the magnification side across the intermediate image Im formed by the first refraction system R1, is composed of a biconvex lens L9, a biconcave lens L8, a biconvex lens L7, a negative meniscus lens L6, a biconvex lens L5, a fourth field stop FS4, a second aperture stop AS2, a fifth field stop FS5, a biconvex lens L4, a biconcave lens L3, a negative meniscus lens L2, and a negative meniscus lens L1, arranged in this order from the reduction side to the magnification side along the optical axis Z. The second refraction system R2 further forms the intermediate image Im on a screen or the like (not shown).

[0165] Detailed data of the components in this Example 5 is shown in Fig. 35. The display method in Fig. 35 is basically the same as that in Figs. 5, 14, and 20, but in Fig. 26, "Im," "PR11," and "IS12" respectively indicate the intermediate image Im, the prism 11, and the image display element 12. Fig. 36 also shows aspherical data regarding the aspherical surfaces in these components. In this Example 5, the aspherical shapes of all aspherical surfaces are expressed by the following equations using the aspherical coefficients shown in Fig. 36. X=(1 / Rdy)R 2 / [1+{1-(1+K)(1 / Rdy) 2 R 2} 1 / 2 ] +A4R 4 +A6R 6 +A8R 8 +A10R 10 +A12R 12 +A14R 14 +A16R 16

[0166] Next, the movement amounts of the zoom group and the focus group will be described with reference to FIG. 37. In FIG. 37, the "s + numerical value" column shows the surface spacing (unit: mm) of the surfaces shown in FIG. 35, and the numerical value indicates the surface number (No.). For example, s2 indicates the surface spacing of the surface with surface number 2, i.e., the lens surface on the reduction side of lens L1, relative to the next surface with number 3. The "ZOOM" notation below each "s + numerical value" column indicates that the surface spacing of that displayed row changes with zooming, and the "FOCUS" notation indicates that the surface spacing of that displayed row changes with focusing. The "Z" column shows six different states of the lens group depending on zooming or focusing. States 1 to 3 indicate states where the lens is focused on the closest screen or the like that can be focused on, and states 4 to 6 indicate states where the lens is focused on the farthest screen or the like that can be focused on. Moreover, states 1 and 4 are wide-angle end states set by zooming, states 2 and 5 are intermediate states between the wide-angle end and the telephoto end, and states 3 and 6 are telephoto end states.

[0167] Similar to the case of the above-described Example 1, a more detailed configuration of Example 5 is shown in Figure 42. Furthermore, as data on lenses near the aperture stop in Example 5, data on the first and second adjacent lenses of groups 1 and 2 relative to aperture stop AS1, and the first and second adjacent lenses of groups 3 and 4 relative to aperture stop AS2 are shown in Figures 43, 44, and 45. In Example 5, the second adjacent lens and first adjacent lens of group 1, the first adjacent lens and second adjacent lens of group 2, the second adjacent lens and first adjacent lens of group 3, and the first adjacent lens and second adjacent lens of group 4, in order from the reduction side to the enlargement side, are specifically shown as lenses L18, L17, L16, L15, L6, L5, L4, and L3, respectively.

[0168] That is, the data shown in Fig. 42 are for a configuration in which lenses L7, L8, L9, and L10 in the diagram shown in Fig. 47(1) are lenses L18, L17, L16, and L15 of this Example 5, respectively, and lenses L22, L23, L24, and L25 in the diagram shown in Fig. 47(2) are lenses L6, L5, L4, and L3 of this Example 5, respectively. Fig. 43 shows the glass materials of lenses L18 and L17 as the second and first adjacent lenses in group 1, lenses L16 and L15 as the first and second adjacent lenses in group 2, lenses L6 and L5 as the second and first adjacent lenses in group 3, and lenses L4 and L3 as the first and second adjacent lenses in group 4 in this Example 5, Fig. 44 shows the values ​​of internal transmittance τ420 of those glass materials, and Fig. 45 shows the relative temperature coefficients dn / dt of the refractive index of those glass materials. As shown in FIGS. 44 and 45, all of the lenses included in groups 1 to 4 of this fifth embodiment satisfy either formula (25) or formula (26), and also satisfy formula (28).

[0169] Figure 46 also shows the anomalous dispersion θg,F of the main lenses in this Example 5. In this Example 5, four lenses, L23, L22, L20, and L18, are listed as positive lenses arranged on the reduction side of aperture stop AS1, which is the first stop, and two lenses, L9 and L7, are listed as positive lenses arranged on the enlargement side of aperture stop AS1, and the anomalous dispersion θg,F of these lenses is shown. As shown in Figure 46, the imaging optical system 500 of this Example 5 satisfies formulas (38) and (40).

[0170] Next, aberrations in the imaging optical system 500 of this fifth embodiment will be described. Fig. 38 shows, from left to right, spherical aberration, astigmatism, and distortion when the imaging optical system 500 of this fifth embodiment is at the wide-angle end. Fig. 39 shows lateral aberration when the imaging optical system 500 is at the wide-angle end. As shown in Figs. 38 and 39, spherical aberration, astigmatism, distortion, and lateral aberration are well corrected.

[0171] Furthermore, Fig. 40 shows, from left to right, the spherical aberration, astigmatism, and distortion when the imaging optical system 500 of this embodiment 5 is at the telephoto end. Fig. 41 shows the lateral aberration when the imaging optical system 500 is at the telephoto end. As shown in Figs. 40 and 41, the spherical aberration, astigmatism, distortion, and lateral aberration are well corrected.

[0172] Although the present invention has been described above with reference to embodiments and examples, the imaging optical system of the present invention is not limited to the above embodiments and examples and can be modified in various ways, for example, the radius of curvature, surface spacing, refractive index, and Abbe number of each lens can be changed as appropriate. Furthermore, the projection device to which the imaging optical system of the present invention is applied can also be modified in various ways, for example, with respect to the light valves used and the optical members used for light beam separation or light beam combination.

[0173] Various modifications will now be described with reference to Fig. 48, which shows the schematic configuration of an imaging optical system to which the present invention can be applied. In the schematic configuration shown in Fig. 48, lens 51 is disposed as a fixed group on the most reduction side of lens barrel 50, and rear group frame 55, which holds lenses 52, 53, and 54, is engaged with lens barrel 50 via engagement portion 56. Furthermore, aperture group frame 60, which holds field stop 57, aperture stop 58, and field stop 59, is engaged with lens barrel 50 via engagement portion 61. Furthermore, front group frame 63, which holds lens 62 on the most enlargement side, is engaged with lens barrel 50 via engagement portion 64.

[0174] When the above-described configuration is applied to a projection device, there are often mechanical limitations on the rear portion of the imaging optical system due to considerations such as the illumination system components of the projection device body. Therefore, the suspension position of the rear group frame 55 (the position where it engages with the lens barrel 50) tends to be forward of the center of gravity of the group, that is, toward the magnification side. Taking this tendency into consideration, providing a stop in front of the rear group frame 55 improves the balance of weight distribution, suppresses tilt of the rear group frame 55, and improves the yield of the imaging optical system.

[0175] Furthermore, diaphragms such as the aperture diaphragm 58 become heat-generating bodies because they block light. For this reason, it is desirable to arrange the diaphragm group frame 60 independently, separate from the rear group frame 55 and the front group frame 63. This prevents heat from being transferred to the rear and front group lenses, making it possible to suppress fluctuations in the lens focal length due to heat.

[0176] The lenses in the rear group block some of the light and generate heat. Anomalous dispersion glass is generally used for the positive lenses in the rear group, but because anomalous dispersion glass has a large negative temperature coefficient of refractive index dn / dt, the back focal length of the rear group increases when the temperature becomes high. In contrast, glass material with a positive temperature coefficient of refractive index dn / dt is used for the positive lenses in the front group. Therefore, if a light-blocking, heat-generating aperture is placed in the front group and the heat from this aperture is transferred to the lenses in the front group, it is possible to correct focus shifts caused by the rear group.

[0177] Furthermore, the rear group frame 55 and the front group frame 63 are preferably provided with a temperature-dependent focus correction mechanism made of a material that expands and contracts with temperature differently from metal, such as a POM (polyacetal) tube or a bimetal spring.

[0178] It is also preferable to provide an adjustment mechanism for one of the multiple lens groups that move as a focus group, separate from the regular (product) focus mechanism used by users of the imaging optical system. This adjustment mechanism allows fine adjustment of performance within the manufacturing process of the imaging optical system, thereby improving yield.

[0179] Furthermore, when the imaging optical system according to the present invention is applied to a projection device, it is preferable to provide an auxiliary temperature correction mechanism in consideration of the influence of room temperature fluctuations on the entire projection device.

[0180] Although the embodiments and examples of the imaging optical system of the present invention applied to a projection device have been described above, the imaging optical system of the present invention can also be applied to an imaging device. Specifically, by arranging an imaging element at the position where the image display element is arranged in each example and irradiating light from the magnification side of the imaging optical system of the present invention, it becomes possible to form a reduced image on the imaging element. [Explanation of symbols]

[0181] 1 Image display surface 2, 12 Image display element 3, 11 Prism 4, 5 Glass Blocks 6 concave mirror 100, 200, 300, 400, 500 Imaging optical system AS1 First Aperture Stop AS2 Second Aperture Stop FS1~FS5 field stop IM intermediate image IM1 1st intermediate image IM2 2nd intermediate image L1~L27 lenses OP1 1st optical system OP2 2nd optical system R1 First refraction system R2 Second refraction system Z optical axis f1~f4 focus group z1~z6 zoom group

Claims

1. An imaging optical system that forms an image on a reduction-side conjugate plane on a magnification-side conjugate plane, the imaging optical system includes a first optical system that includes an intermediate image therein and that has a first refractive system disposed on a reduction side of the intermediate image and a second refractive system disposed on a magnification side thereof, the first refractive system has a first aperture, and the second refractive system has a second aperture; Lens surfaces are arranged adjacent to the first and second apertures on both the reduction side and the enlargement side, An imaging optical system that satisfies the following expressions (1) to (8): 1.5 < Y1-1...(1) 1.5 < Y1-2...(2) 1.0 < Y2-1...(3) 0.5 < Y2-2...(4) 0.5 < Y1-1 / |fw|...(5) 0.5 < Y1-2 / |fw|...(6) 0.3 < Y2-1 / |fw|...(7) 0.1 < Y2-2 / |fw|...(8) however, Y1-1: absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 1 adjacent to the reduction side of the first aperture (unit: mm), Y1-2: Absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays incident on the lens surface 2 adjacent to the enlargement side of the first aperture (unit: mm), Y2-1: absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 3 adjacent to the reduction side of the second aperture (unit: mm), Y2-2: Absolute value of the height of the chief ray at the most peripheral angle of view among the rays of light incident on the lens surface 4 adjacent to the enlargement side of the second aperture (unit: mm)

2. 2. The imaging optical system according to claim 1, which satisfies the following expressions (9) to (12): 5.0 < D1-1...(9) 5.0 < D1-2...(10) 1.0 < D2-1...(11) 1.0 < D2-2...(12) however, D1-1: Distance from the first aperture to the lens surface 1 adjacent to the reduction side of the first aperture (unit: mm) D1-2: Distance from the first aperture to the lens surface 2 adjacent to the first aperture on the enlargement side (unit: mm) D2-1: Distance from the second aperture to the lens surface 3 adjacent to the reduction side of the second aperture (unit: mm) D2-2: Distance from the second aperture to the lens surface 4 adjacent to the enlargement side of the second aperture (unit: mm)

3. 3. The imaging optical system according to claim 2, wherein the following formula (13) is satisfied: Ds2 < Ds1...(13) however, Ds1: D1-1 + D1-2 Ds2: D2-1 + D2-2

4. 4. The imaging optical system according to claim 1, wherein the following expressions (14) to (16) are satisfied: 1.0 < tanθ1× | fw | < 3.0 (14) 2.5 < tanθ2× | fw | < 6.0 (15) 1.5 < tanθ2 / tanθ1 < 4.0 (16) however, θ1: the angle of incidence of the chief ray at the most peripheral angle of view to the first aperture, θ2: the angle of incidence of the chief ray at the most peripheral angle of view to the second aperture, fw: focal length of the entire system at the wide-angle end and closest focusing

5. 5. The imaging optical system according to claim 4, wherein the following formula (17) is satisfied: 5.0 < Ds1 × tanθ1 < 20.0 (17)

6. An imaging optical system that forms an image on a reduction-side conjugate plane on a magnification-side conjugate plane, the imaging optical system includes a first optical system that includes an intermediate image therein and that has a first refractive system disposed on a reduction side of the intermediate image and a second refractive system disposed on a magnification side thereof, the first refractive system has a first aperture, and the second refractive system has a second aperture; Lens surfaces are arranged adjacent to the first and second apertures on both the reduction side and the enlargement side, An imaging optical system that satisfies the following expressions (1) to (4), (14) to (16), and (18). 1.5 < Y1-1...(1) 1.5 < Y1-2...(2) 1.0 < Y2-1...(3) 0.5 < Y2-2...(4) 1.0 < tanθ1× | fw | < 3.0 (14) 2.5 < tanθ2× | fw | < 6.0 (15) 1.5 < tanθ2 / tanθ1 < 4.0 (16) 8.0 < Ds2 × tanθ2 < 30.0 (18) however, Y1-1: absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 1 adjacent to the reduction side of the first aperture (unit: mm), Y1-2: Absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays incident on the lens surface 2 adjacent to the enlargement side of the first aperture (unit: mm), Y2-1: absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 3 adjacent to the reduction side of the second aperture (unit: mm), Y2-2: Absolute value of the height of the chief ray at the most peripheral angle of view among the rays of light incident on the lens surface 4 adjacent to the enlargement side of the second aperture (unit: mm) θ1: the angle of incidence of the chief ray at the most peripheral angle of view to the first aperture, θ2: the angle of incidence of the chief ray at the most peripheral angle of view to the second aperture, fw: focal length of the entire system at the wide-angle end and closest focusing, Ds2: D2-1+D2-2, D2-1: distance from the second aperture stop to the lens surface 3 adjacent to the reduction side of the second aperture stop (unit: mm), D2-2: Distance from the second aperture to the lens surface 3 adjacent to the enlargement side of the second aperture (unit: mm)

7. 7. The imaging optical system according to claim 1, which satisfies the following expressions (19) and (20): 0.9 ≦ φs1-1 / φs1 <2.0 (19) 0.9 ≦ φs1-2 / φs1 <2.0 (20) however, φs1: opening diameter of the first aperture φs1-1: effective diameter of the lens adjacent to the first aperture on the reduction side φs1-2: Effective diameter of the lens adjacent to the first aperture on the enlargement side

8. 8. The imaging optical system according to claim 7, which satisfies the following expressions (21) and (22): 0.8 ≦ φs2-1 / φs2 <2.5 (21) 0.8 ≦ φs2-2 / φs2 <2.5 (22) however, φs2: aperture diameter of second aperture φs2-1: effective diameter of the lens adjacent to the second aperture on the reduction side φs2-2: Effective diameter of the lens adjacent to the second aperture on the enlargement side

9. 9. The imaging optical system according to claim 1, wherein the following formula (23) is satisfied: 0.5 < Y2-2 × tanθ2 (23)

10. 9. The imaging optical system according to claim 1, wherein the following formula (24) is satisfied: 0.5 < D2-2 / Y2-2...(24)

11. 11. The imaging optical system according to claim 1, wherein the first adjacent lens disposed adjacent to the aperture stop and the second adjacent lens disposed adjacent to the first adjacent lens in a direction away from the aperture stop do not include a cemented lens.

12. An imaging optical system that forms an image on a reduction-side conjugate plane on a magnification-side conjugate plane, the imaging optical system includes a first optical system that includes an intermediate image therein and that has a first refractive system disposed on a reduction side of the intermediate image and a second refractive system disposed on a magnification side thereof, the first refractive system has a first aperture, and the second refractive system has a second aperture; Lens surfaces are arranged adjacent to the first and second apertures on both the reduction side and the enlargement side, the first adjacent lens disposed adjacent to the aperture stop and the second adjacent lens disposed adjacent to the first adjacent lens in a direction away from the aperture stop do not include a cemented lens; The entire imaging optical system does not include any cemented lenses. An imaging optical system that satisfies the following expressions (1) to (4): 1.5 < Y1-1...(1) 1.5 < Y1-2...(2) 1.0 < Y2-1...(3) 0.5 < Y2-2...(4) however, Y1-1: absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 1 adjacent to the reduction side of the first aperture (unit: mm), Y1-2: Absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays incident on the lens surface 2 adjacent to the enlargement side of the first aperture (unit: mm), Y2-1: absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 3 adjacent to the reduction side of the second aperture (unit: mm), Y2-2: Absolute value of the height of the chief ray at the most peripheral angle of view among the rays of light incident on the lens surface 4 adjacent to the enlargement side of the second aperture (unit: mm)

13. two lenses, a first adjacent lens disposed adjacent to the first aperture stop on the reduction side and a second adjacent lens disposed adjacent to the first adjacent lens on the reduction side, are defined as group 1; two lenses consisting of a first adjacent lens arranged adjacent to the first aperture stop on the enlargement side and a second adjacent lens arranged adjacent to the first adjacent lens on the enlargement side are defined as group 2; a first adjacent lens disposed adjacent to the second aperture stop on the reduction side, and a second adjacent lens disposed adjacent to the first adjacent lens on the reduction side, the two lenses being grouped as group 3; When two lenses consisting of a first adjacent lens arranged adjacent to the second aperture stop on the enlargement side and a second adjacent lens arranged adjacent to the first adjacent lens on the enlargement side are grouped as group 4, 13. The imaging optical system according to claim 1, wherein the lenses included in groups 1, 2, 3, and 4 satisfy the following formula (25) or (26): 40≦νd and 0.97<τ420 (25) νd<40 and 0.90<τ420 ... (26) however νd: Abbe number of the optical material that constitutes the lens τ420: Internal transmittance of an optical material with a thickness of 10.0 mm at a wavelength of 420 nm

14. 14. The imaging optical system according to claim 13, wherein the following formula (27) is satisfied when the formula (26) is satisfied: νd<40 and 0.93<τ420 (27)

15. When the temperature coefficient of the relative refractive index of the optical material is dn / dt, All lenses in the lens group satisfy |dn / dt| < 6.5 (28) 15. The imaging optical system according to claim 13, wherein the following is satisfied:

16. 16. The imaging optical system according to claim 1, wherein at least one of the positive lenses arranged on the reduction side of the first aperture satisfies the following expression (29): 65.0<νd and 0.005<θg,F (29) however, νd: Abbe number at d line (587.6 nm) of the optical material of the positive lens θg,F: Anomalous dispersion of the optical material of the positive lens

17. 17. The imaging optical system according to claim 1, wherein at least one of the positive lenses arranged on the enlargement side of the first aperture satisfies the following formula (30): 65.0<νd and 0.005<θg,F (30) however, νd: Abbe number at d line (wavelength 587.6 nm) of the optical material of the positive lens θg,F: Anomalous dispersion of the optical material of the positive lens

18. the imaging optical system includes one or more zoom groups that move during magnification change; Among the zoom groups on the reduction side of the first refractive system with respect to the stop, the first zoom group having the largest number of lenses has a positive focal length, the first zoom group does not include a lens on the enlargement side of the first aperture, but includes a lens on the reduction side; The imaging optical system according to any one of claims 1 to 17.

19. A fixed group 1 having a positive focal length that does not move during zooming is disposed on the most reduction side of the imaging optical system. The imaging optical system according to claim 18.

20. An imaging optical system that forms an image on a reduction-side conjugate plane on a magnification-side conjugate plane, the imaging optical system includes a first optical system that includes an intermediate image therein and that has a first refractive system disposed on a reduction side of the intermediate image and a second refractive system disposed on a magnification side thereof, the first refractive system has a first aperture, and the second refractive system has a second aperture; Lens surfaces are arranged adjacent to the first and second apertures on both the reduction side and the enlargement side, the imaging optical system includes one or more zoom groups that move during magnification variation; Among the zoom groups on the reduction side of the first refractive system with respect to the stop, the first zoom group having the largest number of lenses has a positive focal length, the first zoom group does not include a lens on the enlargement side relative to the first aperture stop, but includes a lens on the reduction side; A fixed group 1 having a positive focal length that does not move during zooming is disposed on the most reduction side of the imaging optical system, The fixed group 1 includes at least one negative lens, An imaging optical system that satisfies the following expressions (1) to (4): 1.5 < Y1-1...(1) 1.5 < Y1-2...(2) 1.0 < Y2-1...(3) 0.5 < Y2-2...(4) however, Y1-1: absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 1 adjacent to the reduction side of the first aperture (unit: mm), Y1-2: Absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays incident on the lens surface 2 adjacent to the enlargement side of the first aperture (unit: mm), Y2-1: absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 3 adjacent to the reduction side of the second aperture (unit: mm), Y2-2: Absolute value of the height of the chief ray at the most peripheral angle of view among the rays of light incident on the lens surface 4 adjacent to the enlargement side of the second aperture (unit: mm)

21. a second zoom group disposed adjacent to the first aperture stop on the enlargement side; The second zoom group is made up of a positive lens.

21. The imaging optical system according to claim 18.

22. the positive lens constituting the second zoom group is made of a positive meniscus lens having a concave surface toward the image side; 22. The imaging optical system according to claim 21.

23. The first zoom group and the second zoom group move independently during zooming.

23. The imaging optical system according to claim 21 or 22.

24. The final zoom group, which is the zoom group closest to the magnification side, includes a negative lens element.

24. The imaging optical system according to claim 18.

25. the negative lens is disposed on the most magnification side of the final zoom group; 25. The imaging optical system according to claim 24.

26. The final zoom group consists of only negative lenses 26. The imaging optical system according to claim 25.

27. A fixed group 2 is disposed adjacent to the final zoom group on the magnification side.

27. The imaging optical system according to claim 26.

28. The fixed group 2 includes a negative meniscus aspheric lens.

28. The imaging optical system according to claim 27.

29. the negative meniscus lens included in the first refractive system has a center-to-periphery lens thickness ratio (uneven thickness ratio) of 1.5 or more; 29. The imaging optical system according to claim 28.

30. The imaging optical system has at least one focus group that moves during focusing, the at least one focus group includes a reduction-side focus group disposed in the first refractive system; 30. The imaging optical system according to claim 1.

31. At least one focus group includes a magnification-side focus group disposed in the second refractive system.

31. The imaging optical system according to claim 30.

32. at least one focus group includes an intermediate focus group including a lens on the most enlargement side of the first refractive system and a lens on the most reduction side of the second refractive system; an intermediate image is formed within the intermediate focus group; 32. The imaging optical system according to claim 30 or 31.

33. An imaging optical system that forms an image on a reduction-side conjugate plane on a magnification-side conjugate plane, the imaging optical system includes a first optical system that includes an intermediate image therein and that has a first refractive system disposed on a reduction side of the intermediate image and a second refractive system disposed on a magnification side thereof, the first refractive system has a first aperture, and the second refractive system has a second aperture; Lens surfaces are arranged adjacent to the first and second apertures on both the reduction side and the enlargement side, the imaging optical system has at least one focus group that moves during focusing; the at least one focus group includes a reduction-side focus group disposed in the first refractive system; at least one focus group includes an intermediate focus group including a lens on the most enlargement side of the first refractive system and a lens on the most reduction side of the second refractive system; an intermediate image is formed within the intermediate focus group, The intermediate focus group is A positive meniscus lens with its convex surface facing the magnification side is placed on the reduction side of the intermediate image, A positive meniscus lens with its convex surface facing the reduction side is placed on the magnification side of the intermediate image, An imaging optical system that satisfies the following expressions (1) to (4): 1.5 < Y1-1...(1) 1.5 < Y1-2...(2) 1.0 < Y2-1...(3) 0.5 < Y2-2...(4) however, Y1-1: absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 1 adjacent to the reduction side of the first aperture (unit: mm), Y1-2: Absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays incident on the lens surface 2 adjacent to the enlargement side of the first aperture (unit: mm), Y2-1: absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 3 adjacent to the reduction side of the second aperture (unit: mm), Y2-2: Absolute value of the height of the chief ray at the most peripheral angle of view among the rays of light incident on the lens surface 4 adjacent to the enlargement side of the second aperture (unit: mm)

34. the intermediate focus group further includes a negative meniscus lens disposed between the meniscus lens having a convex surface facing the enlargement side and the intermediate image; 34. The imaging optical system according to claim 33.

35. The final focus group, which is located on the most enlargement side, is located adjacent to the reduction side of the second aperture.

35. The imaging optical system according to any one of claims 30 to 34.

36. the final focus group is composed of three lenses: a positive, a negative, and a positive; 36. The imaging optical system according to claim 35.

37. The lens group on the enlargement side of the second aperture stop is a fixed group 3 that does not move during zooming or focusing.

37. The imaging optical system according to any one of claims 30 to 36.

38. the imaging optical system is configured such that a second optical system including a reflecting optical element is disposed on the enlargement side of the first optical system; 38. The imaging optical system according to any one of claims 1 to 37.

39. An imaging optical system that forms an image on a reduction-side conjugate plane on an enlargement-side conjugate plane, the imaging optical system includes a first optical system that includes an intermediate image therein and that has a first refractive system disposed on a reduction side of the intermediate image and a second refractive system disposed on a magnification side thereof, the first refractive system has a first aperture, and the second refractive system has a second aperture; Lens surfaces are arranged adjacent to the first and second apertures on both the reduction side and the enlargement side, a second optical system including a reflecting optical element is disposed on the magnification side of the first optical system; the second optical system includes a concave mirror; the concave mirror is disposed on the enlargement side of a second intermediate image formed by the imaging action of the first optical system, An imaging optical system that satisfies the following expressions (1) to (4): 1.5 < Y1-1...(1) 1.5 < Y1-2...(2) 1.0 < Y2-1...(3) 0.5 < Y2-2...(4) however, Y1-1: absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 1 adjacent to the reduction side of the first aperture (unit: mm), Y1-2: Absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays incident on the lens surface 2 adjacent to the enlargement side of the first aperture (unit: mm), Y2-1: absolute value of the ray height of the chief ray at the most peripheral angle of view among the rays emerging from the lens surface 3 adjacent to the reduction side of the second aperture (unit: mm), Y2-2: Absolute value of the height of the chief ray at the most peripheral angle of view among the rays of light incident on the lens surface 4 adjacent to the enlargement side of the second aperture (unit: mm)

40. the reflective optical element comprises a prism having a solid structure and a total internal reflection surface; The prism has two reflecting surfaces, and all incident light is transmitted to the next surface by total reflection at either surface. the prism is disposed between the first optical system and the concave mirror; 40. The imaging optical system according to claim 39.

41. an imaging optical system according to any one of claims 1 to 40; an image display element disposed at a reduction-side conjugate plane position of the imaging optical system; A projection device having:

42. an imaging optical system according to any one of claims 1 to 40; an image sensor disposed at a reduction-side conjugate plane of the imaging optical system; An imaging device having the above configuration.

Images