Optical system in which an intermediate image is formed

Abstract

Provided is an optical system (10) comprising a first optical subsystem (RS1) disposed on a magnification side (3) and a second optical subsystem (RS2) disposed on a reduction side (2), with an intermediate image (IM) interposed therebetween. The first optical subsystem includes: a first lens group (G1) that is disposed on the magnification side of a first stop (ST1), with a first space (SP1), which is a space in which another lens could be disposed but in which another lens is not disposed, therebetween, and that is provided with, on the magnification side, a first component (G1f) having negative refractive power; and a second lens group (G2) that has positive refractive power, the second lens group being disposed on the reduction side of the first stop, with a second space (SP2), which is a space in which another lens could be disposed but in which another lens is not disposed, therebetween, and the intermediate image (IM) being formed adjacent to the reduction side of the second lens group in a manner inclining toward the magnification side.

Description

[Technical field]

[0001] The present invention relates to an optical system in which an intermediate image is formed. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2015-152890 discloses a zoom optical system that utilizes a reimaging method, has high optical performance over a wide angle of view over the entire zoom range, and is easy to miniaturize. The zoom optical system is composed of, in order from the magnification conjugate side to the reduction conjugate side, a first optical system and a second optical system having a zoom function, and has an optical action in which an enlargement conjugate point on the enlargement conjugate side is imaged at an intermediate imaging position between the first optical system and the second optical system, and the image imaged at the intermediate imaging position is reimaged at a reduction conjugate point on the reduction conjugate side. The second optical system is composed of, in order from the magnification conjugate side to the reduction conjugate side, a lens group with positive refractive power, a lens group with positive refractive power, and a lens group with positive refractive power. DISCLOSURE OF THEINVENTION

[0003] There is a demand for an optical system in which an intermediate image is formed internally, which is more compact and has a configuration in which various aberrations can be easily corrected.

[0004] One aspect of the present invention is an optical system having a first optical subsystem arranged on the enlargement side with an intermediate image therebetween, and a second optical subsystem arranged on the reduction side. The first optical subsystem includes a first lens group arranged on the enlargement side at a first interval from the first aperture where other lenses can be arranged, but where no other lenses are arranged, and a second lens group with positive refractive power arranged on the reduction side at a second interval from the first aperture where other lenses can be arranged, but where no other lenses are arranged. The first lens group includes a first component of negative refractive power on the enlargement side. An intermediate image is formed adjacent to the reduction side of the second lens group so as to be inclined toward the enlargement side.

[0005] A retrofocus type with a negative-positive power arrangement in which the negative refractive power component is arranged on the magnification side (magnification conjugate side) can provide an optical system with a large wide angle of view on the magnification side and a long back focus on the reduction side, making it telecentric or close to it. On the other hand, in addition to the large lens diameter on the magnification side, when an optical system with positive power on the reduction side is composed of multiple lenses, the difference in diameter between the lenses is large and the spacing is wide. This results in poor space efficiency for the optical system, making it difficult to arrange multiple lenses efficiently and compactly.

[0006] In contrast, in the optical system of the present invention, a first aperture is provided between a first lens group having a negative component and a second lens group having positive refractive power, near where the peripheral light and central light intersect to concentrate the light beam, and first and second gaps are provided before and after the first aperture in which lenses can be placed, and by not placing lenses in these gaps, the difference in diameter of the lenses that make up the second lens group having positive refractive power is reduced.

[0007] Furthermore, by noting that an intermediate image is formed on the reduction side of the first optical subsystem, the intermediate image is formed so as to be tilted to the enlargement side. In general, when designing an optical system, it is aimed to reduce the Petzval sum. In this optical system, the Petzval sum of the first lens group is positive, and the intermediate image is tilted to the reduction side. Therefore, the Petzval sum of the second lens group is negative to cancel the inclination of the intermediate image. In this case, by setting the Petzval sum of the second lens group to a range in which the intermediate image is tilted to the enlargement side, it is possible to relatively over-adjust the Petzval sum of the second lens group in the direction in which the positive power of the second lens group increases. Therefore, a configuration in which many lens surfaces are arranged in a narrow space can be adopted as the second lens group, and a wide-angle optical system that is highly space-efficient, compact, and has a high aberration correction ability can be provided.

[0008] The optical system may be arranged such that the optical axis extends in a straight line. The optical system may include a bending optical element, typically a mirror or a prism, that changes the direction of the optical axis, and the optical axis may be bent into an L-shape or a U-shape. The optical system may be an optical system for a projector, and another aspect of the present application is a projector having the optical system and a light modulator arranged on the reduction side of the optical system. The optical system may be an optical system for imaging, and yet another aspect of the present application is an imaging device having the optical system and an imaging element arranged on the reduction side of the optical system. [Brief description of the drawings]

[0009] [Figure 1] 1A and 1B are diagrams illustrating an example of an optical system and an apparatus including the optical system. [Diagram 2] FIG. 2 is a diagram showing lens data of the optical system shown in FIG. [Diagram 3] FIG. 2 is a diagram showing aspheric data of the optical system shown in FIG. [Figure 4] FIG. 2 is a diagram showing the distances before and after each group that moves during focusing and zooming of the optical system shown in FIG. 1. [Diagram 5] 2 is a diagram showing the field curvature of an intermediate image of the optical system shown in FIG. 1. [Figure 6] 2A to 2C are diagrams showing various aberrations at the wide-angle end (Wide) and telephoto end (Tele) of the optical system shown in FIG. [Figure 7] 2A to 2C are diagrams showing lateral aberration at each image height at the wide-angle end of the optical system shown in FIG. [Figure 8] 2A to 2C are diagrams showing lateral aberration at various image heights at the telephoto end of the optical system shown in FIG. [Figure 9] FIG. 13 is a diagram showing another example of a focus group. [Figure 10] FIG. 13 is a diagram showing another example of an optical system and an apparatus including the optical system. [Figure 11] FIG. 11 is a diagram showing lens data of the optical system shown in FIG. [Figure 12] 11 is a diagram showing aspheric data of the optical system shown in FIG. 10. [Figure 13]11 is a diagram showing the distances before and after each group that moves during focusing and zooming of the optical system shown in FIG. 10. [Figure 14] 11 is a diagram showing the field curvature of an intermediate image of the optical system shown in FIG. [Figure 15] 11A to 11C are diagrams showing various aberrations at the wide-angle end (Wide) and telephoto end (Tele) of the optical system shown in FIG. [Figure 16] 11A to 11C are lateral aberration diagrams at various image heights at the wide-angle end (wide) of the optical system shown in FIG. [Figure 17] 11A to 11C are lateral aberration diagrams at various image heights at the telephoto end of the optical system shown in FIG. [Figure 18] FIG. 13 is a diagram showing another example of an optical system and an apparatus including the optical system. [Figure 19] FIG. 19 is a diagram showing lens data of the optical system shown in FIG. [Figure 20] FIG. 19 is a diagram showing aspheric data of the optical system shown in FIG. [Figure 21] 19 is a diagram showing the distances before and after each group that moves during focusing and zooming of the optical system shown in FIG. 18. [Figure 22] 19 is a diagram showing the field curvature of an intermediate image of the optical system shown in FIG. 18. [Figure 23] 19A to 19C are diagrams showing various aberrations at the wide-angle end (Wide) and telephoto end (Tele) of the optical system shown in FIG. 18. [Figure 24] 19A to 19C are lateral aberration diagrams at various image heights at the wide-angle end (wide) of the optical system shown in FIG. 18. [Diagram 25] 19A to 19C are lateral aberration diagrams at various image heights at the telephoto end of the optical system shown in FIG. 18. [Figure 26] FIG. 13 is a diagram showing another example of an optical system and an apparatus including the optical system. [Figure 27] FIG. 27 is a diagram showing lens data of the optical system shown in FIG. 26. [Figure 28] FIG. 27 is a diagram showing aspheric data of the optical system shown in FIG. 26. [Figure 29] 27 is a diagram showing the spacing before and after each group that moves during focusing and zooming of the optical system shown in FIG. 26. [Diagram 30] 27 is a diagram showing the field curvature of an intermediate image of the optical system shown in FIG. 26. [Diagram 31]27A to 27C are diagrams showing various aberrations at the wide-angle end (Wide) and telephoto end (Tele) of the optical system shown in FIG. 26. [Diagram 32] 27A to 27C are lateral aberration diagrams at various image heights at the wide-angle end (wide) of the optical system shown in FIG. 26. [Diagram 33] 27A to 27C are lateral aberration diagrams at various image heights at the telephoto end of the optical system shown in FIG. 26. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be further described with reference to the drawings. FIG. 1 shows an apparatus including an optical system according to an embodiment of the present invention. An example of the apparatus is a projector 1, which includes an optical system 10 and an optical modulator (light valve) 5 arranged on a reduction side 2. The optical system 10 for the projector forms an intermediate image IM at a position in the optical system 10 that is conjugate with the image surface 5a of the optical modulator 5, and further outputs the intermediate image IM from the enlargement side 3 as projection light 19 and projects the intermediate image on a screen or a wall surface (not shown) to form an enlarged image again. The light valve 5 may be an LCD, a digital mirror device (DMD), an organic EL, or the like, as long as it can form an image, and may be a single-panel type or a type that forms an image of each color separately. The light valve 5 may be of a light-emitting type or a lighting type. In the case of a lighting type, the projector 1 may further include a lighting optical system (not shown). The screen may be a wall surface or a whiteboard, and the projector 1 may be a front projector or a rear projector including a screen.

[0011] Another example of a device is an imaging device 21, which has an optical system 10 and an imaging element 25 arranged on the reduction side 2. The optical system 10 for the imaging device forms an intermediate image IM at a position conjugate with the imaging surface 25a of the imaging element 25, which is the reduction-side image formation surface, using light incident from the enlargement side (object side) 3, and further forms an image again on the imaging surface 25a. The configuration and function of the optical system 10 are common whether it is an optical system for an imaging device or an optical system for a projector, so hereinafter, a further explanation will be given using the projector 1 and the optical system 10 for a projector as examples.

[0012] The optical system 10 has a first optical subsystem, a first refractive optical system RS1 in this example, arranged on the enlargement side 3 with the intermediate image IM in between, and a second optical subsystem, a second refractive optical system RS2 in this example, arranged on the reduction side 2. The first refractive optical system RS1 and the second refractive optical system RS2 each include a plurality of lenses constituting a plurality of lens groups. In the following, an example in which each of the optical subsystems RS1 and RS2 is composed of a plurality of lenses is described. Each of the optical subsystems RS1 and RS2 may include a mirror or prism for bending the optical axis, and may include a mirror surface having a power to refract a light beam together with or instead of a lens.

[0013] In this example, the first refractive optical system RS1 includes a first lens group G1 having a first component (sub lens group) G1f of negative refractive power arranged on the enlargement side (enlargement conjugate side) 3 with a first space SP1 at which other lenses can be arranged from the first aperture ST1, and a second lens group G2 having positive refractive power (composite refractive power) arranged on the reduction side (reduction conjugate side) 2 with a second space SP2 at which other lenses can be arranged from the first aperture ST1, and a second lens group G2 having positive refractive power (composite refractive power). An intermediate image IM is formed adjacent to the reduction side 2 of the second lens group G2. An example of the first lens group G1 is composed of four lenses L11 to L14, and an example of the second lens group G2 is composed of six lenses L21 to L26.

[0014] Specifically, an example of the first lens group G1 includes, from the enlargement side 3, a first sub-lens group G1f including lenses L11 to L13 with a negative-negative-negative power arrangement, and a lens L14 with a positive power. An example of the first lens group G1 includes, arranged in order from the enlargement side 3, negative meniscus lenses L11 and L12 convex toward the enlargement side 3, a biconcave negative lens L13, and a biconvex positive lens L14. An example of the second lens group G2 includes, from the enlargement side 3, lenses L21 to L23 with a positive-positive-negative power arrangement, and lenses L24 to L26 with a positive-negative-positive power arrangement, and the lenses L24 to L26 configure a second component (second sub-lens group) G2r. An example of the second lens group G2 includes, arranged in order from the enlargement side 3, biconvex positive lenses L21 and L22, a negative meniscus lens L23 convex toward the reduction side 2, a biconvex positive lens L24, a negative meniscus lens L25 convex toward the reduction side 2, and a biconvex positive lens L26.

[0015] The second refractive optical system RS2 includes a third lens group G3 having a third component (sub lens group) G3f of negative refractive power arranged on the enlargement side 3 with a third space SP3 between the second aperture ST2 and the third lens group G3f, and a fourth lens group G4 having positive refractive power arranged on the reduction side 2 with a fourth space SP4 between the second aperture ST2 and the fourth lens group G4. An example of the third lens group G3 is composed of seven lenses L31 to L37, and an example of the fourth lens group G4 is composed of nine lenses L41 to L49.

[0016] Specifically, an example of the third lens group G3 includes a third sub-lens group G3f including lenses L31 to L33 with a positive-negative-negative power arrangement from the enlargement side 3, and lenses L34 to L37 with a negative-positive-positive-positive power arrangement. An example of the third lens group G3 includes, arranged in order from the enlargement side 3, a biconvex positive lens L31, a biconcave negative lens L32, a negative meniscus lens L33 convex to the enlargement side 3, a biconcave negative lens L34, a biconvex positive lens L35, a positive meniscus lens L36 convex to the reduction side 2, and a biconvex positive lens L37. An example of the fourth lens group G4 includes, from the enlargement side 3, positive-negative-negative-positive-negative-positive-positive lenses L41 to L49. An example of the fourth lens group G4 includes, arranged in order from the enlargement side 3, a positive meniscus lens L41 convex toward the reduction side 2, a negative meniscus lens L42 convex toward the reduction side 2, a negative meniscus lens L43 convex toward the enlargement side 3, a biconvex positive lens L44, a biconcave negative lens L45, a biconvex positive lens L46, a negative meniscus lens L47 convex toward the reduction side 2, a positive meniscus lens L48 convex toward the reduction side 2, and a biconvex positive lens L49.

[0017] In this way, the optical system (lens system, optical device) 10 of this example is composed of a total of 26 lenses. In this optical system 10, field stops FS11 and FS12 are arranged before and after the first stop (aperture stop) ST1, and field stops FS21 and FS22 are arranged before and after the second stop (aperture stop) ST2.

[0018] This optical system 10 includes four focus lens groups Fg1-Fg4 arranged on the enlargement side 3 relative to an intermediate fixed lens group Fim, four zoom lens groups Zg1-Zg4 arranged on the reduction side 2, and further includes a terminal fixed lens group Fie on the extreme reduction side 2. The zoom lens groups Zg1-Zg4 move during zooming (variable magnification), and their distance to an image surface, for example, image surface 25a on the reduction side 2, varies. The focus lens groups Fg1-Fg4 do not move during zooming (variable magnification), but move during focusing (focusing). The fixed lens groups Fim and Fie do not move in either case.

[0019] In the optical system 10 of this example, the first focus lens group Fg1 is composed of a single lens L11 with negative power on the most enlargement side 3 of the first lens group G1, and the second focus lens group Fg2 is composed of lenses L12-L14 with negative-negative-positive power of the first lens group G1. The third focus lens group Fg3 is composed of the second lens group L21-L26 with positive power including the first aperture ST1. The fourth focus lens group Fg4 is composed of the lens L31 with positive power on the most enlargement side 3 of the third lens group G3, that is, facing the intermediate image IM the most. The intermediate fixed lens group Fim is composed of lenses L32 and L33 with negative power of the third lens group G3.

[0020] The first zoom lens group Zg1 is composed of the negative-positive-positive power lenses L34-L36 of the third lens group G3, and the second zoom lens group Zg2 is composed of the positive power lens L37 of the third lens group G3 on the most reduction side 2. The third zoom lens group Zg3 is composed of the positive-negative power lenses L41 and L42 of the fourth lens group G4 including the second aperture ST2. The fourth zoom lens group Zg4 is composed of the negative-positive-negative-positive-negative-positive lenses L43-L48 of the fourth lens group G4. The final fixed lens group Fie is composed of the positive power lens L49 of the fourth lens group G4 on the most reduction side 2.

[0021] The first refractive optical system (first optical subsystem) RS1 of this optical system 10 is a retrofocus type with a negative-positive power arrangement in which a negative component G1f of refractive power is arranged on the enlargement side (enlargement conjugate side) 3, and an optical subsystem can be obtained in which the enlargement side 3 has a large wide angle of view and the reduction side 2 has a long back focus and is telecentric or close to it. An intermediate image IM is formed adjacent to (without sandwiching another lens) the reduction side (reduction conjugate side) 2 of the first refractive optical system RS1. The intermediate image IM is formed so as to incline toward the enlargement side 3. That is, the intermediate image IM includes a portion of the image formed so that the peripheral image approaches the enlargement side 3 (as the image height increases) with respect to the image on the optical axis 7. Alternatively, the intermediate image IM includes a portion of the image formed so as to approach the enlargement side 3 with respect to the image on the optical axis 7. By forming the intermediate image IM so as to incline toward the enlargement side 3, it is possible to allow the Petzval sum G2PTZ of the second lens group G2 to be a relatively large negative value. Therefore, the second lens group G2 may include a configuration in which multiple refracting surfaces with positive power are concentrated at a short distance. In this optical system 10, the second lens group G2 is configured with positive-positive-negative-positive-negative-positive lenses L21 to L26, and six lenses, including four lenses with positive power, are compactly arranged.

[0022] That is, in this optical system 10, it is possible to include a plurality of negative meniscus lenses convex toward the enlargement side 3 in the first lens group G1. Therefore, the Petzval sum G1PTZ of the first lens group G1 becomes positive, and the intermediate image IM is tilted toward the reduction side (over, the curvature of field is in the positive direction). In contrast, the Petzval sum G2PTZ of the second lens group G2 is relatively excessively negative, and the intermediate image IM is tilted toward the enlargement side (under, the curvature of field is in the negative direction). Therefore, by tilting the intermediate image IM toward the enlargement side, the positive power of the second lens group G2 can be set relatively large. Also, since the Petzval sum G1PTZ is allowed to be large in the first lens group G1, the spread (angle of view) of the light beam in the first lens group G1 can be set large, and the lens diameter of the second lens group G2 can be relatively small. Therefore, as a whole, it is possible to adopt a configuration in which the lens surface is relatively small and densely packed as the second lens group G2. This makes it possible to provide a wide-angle optical system 10 that is compact, has high space efficiency, and has a high aberration correction capability. Note that the above explanation is an explanation of how adjusting the Petzval sum is useful when controlling the tilt direction of the intermediate image IM in this optical system 10. The tilt direction of the intermediate image IM in other optical systems is not determined only by the Petzval sum, but is also influenced by astigmatism and higher-order aberrations. Therefore, there may be cases where the value of the Petzval sum and the tilt direction of the intermediate image IM do not match those explained above.

[0023] The Petzval sum G1PTZ of the first lens group G1 and the Petzval sum G2PTZ of the second lens group G2 may satisfy the following condition (1). 0.6<|G2PTZ / G1PTZ|<1.7···(1) If the lower limit is exceeded, the correction by the second lens group G2 will be insufficient, resulting in a large load on the second optical subsystem RS2, and if the upper limit is exceeded, the correction by the second lens group G2 will be too excessive, resulting in a large load on the second optical subsystem RS2.

[0024] The amount of field curvature IMFc of the intermediate image IM and the focal length (synthetic focal length) f1 of the first refractive optical system RS1 may satisfy the following condition (2). Note that the amount of field curvature IMFc of the intermediate image IM is the amount of field curvature at the maximum angle of view (maximum image height) of the intermediate image IM. 0<|IMFc / f1|<2.5 (2) If the upper limit of condition (2) is exceeded, the amount of field curvature becomes too large, making aberration correction difficult. The upper limit may be 1.5. The amount of field curvature IMFc is controlled by adding astigmatism to the sum of the Petzval sums G1PTZ and G2PTZ.

[0025] The amount of field curvature IMFc of the intermediate image IM and the focal length (synthetic focal length) fw of the optical system 10 at the wide-angle end may satisfy the following condition (3). 0<|IMFc / fw|<2.5···(3) If the upper limits of conditions (2) and (3) are exceeded, the amount of field curvature becomes too large, making it difficult to correct aberrations. The upper limit may be 1.5.

[0026] Furthermore, in the optical system 10, a first aperture ST1 is provided near where the peripheral light and the central light intersect between the first lens group G1 having a negative component and the second lens group G2 having a positive refractive power, and a space is provided before and after the first aperture ST1 where the light flux is concentrated, and no lenses are provided at the space (distance) to reduce the difference in diameter between the lenses L21 to L26 of the second lens group G2. In a retrofocus type lens system, in addition to the lens diameter on the enlargement side being large, when an optical system with positive power on the reduction side is configured with multiple lenses, the difference in diameter between the lenses is large, the space is wide, the space efficiency of the optical system is poor, and it is difficult to efficiently arrange multiple lenses in a compact manner. In this optical system 10, the first aperture ST1 is provided, and spaces SP1 and SP2 are provided before and after the first aperture ST1 where lenses can be arranged but no lenses are arranged, improving the configuration of the second lens group G2.

[0027] The first distance SP1, the second distance SP2, and the effective diameter SD1 of the first aperture ST1 may satisfy the following conditions (4) and (5). 0.5 <SP1 / SD1<1.7···(4) 0.5 <SP2 / SD1<1.7···(5) The first interval SP1 is the distance between the first aperture ST1 and the surface on the reduction side 2 of the lens L14 adjacent thereto on the enlargement side 3, and the second interval SP2 is the distance between the first aperture ST1 and the surface on the enlargement side 3 of the lens L21 adjacent thereto on the reduction side 2. If the lower limits of conditions (4) and (5) are exceeded, the lens surface becomes closer to the aperture ST1, the contribution of light to the lens increases, and problems such as focus deviation become significant. If the upper limits are exceeded, the lens interval becomes too wide, increasing costs and making it difficult to provide a compact optical system. The lower limit may be 0.6.

[0028] Furthermore, by making the surfaces of the first aperture ST1 facing the enlargement side 3 and the reduction side 2 symmetrical, the light flux passing through the aperture ST1 is controlled on both sides, and the decrease in the amount of light caused by the aperture ST1 is suppressed. That is, the surfaces Sf1 and Sr1 in front and behind the first aperture ST1 are made concave or convex with respect to the aperture ST1. In the optical system 10 shown in FIG. 1, the convex surfaces are configured to face each other. In addition, the radius of curvature Sf1r of the lens surface Sf1 on the enlargement side 3 of the first aperture ST1 and the radius of curvature Sr1r of the lens surface Sr1 on the reduction side 2 may satisfy the following condition (6). By arranging the optical surfaces concentrically with respect to the aperture, it is possible to cancel the aberrations occurring on each surface. This becomes difficult if the following condition is not met. 0.1<|Sf1r / Sr1r|<3 (6) If the difference in the radius of curvature between the front and rear surfaces of the first diaphragm ST1 becomes too large, the reduction in the amount of light caused by the diaphragm ST1 tends to become significant.

[0029] Therefore, in the optical system 10, the difference in effective diameter of the lenses L21 to L26 constituting the second lens group G2 can be made small, and a large number of lenses can be arranged in a short space. The maximum effective diameter Dg2max and minimum effective diameter Dg2min of the multiple lenses L21 to L26 in the second lens group G2 may satisfy the following condition (7). 1 <Dg2max / Dg2min<1.7···(7) By reducing the difference between the maximum effective diameter Dg2max and the minimum effective diameter Dg2min, a compact optical system 10 can be provided that can effectively utilize the space within a housing such as a lens barrel that houses the optical system 10.

[0030] The length Lg2 from the enlargement side 3 surface of the lens L21 facing the first aperture ST1 of the second lens group G2 to the reduction side 2 surface of the lens L26 facing the intermediate image IM, and the thickness Lg2p occupied by the multiple lenses of positive refractive power, in this example L21, L22, L24, and L26, may satisfy the following condition (8). 0.5 <Lg2p / Lg2<1.0···(8) By arranging a plurality of lenses, four in this example, having positive refractive power, in the second lens group G2 having positive refractive power with only a minimal air gap, a large number of surfaces capable of correcting aberrations can be arranged in a small area. Therefore, it is possible to provide an optical system 10 having a compact second lens group G2 with high aberration correction capability. The lower limit of condition (8) may be 0.7, and the upper limit may be 0.96. In addition, chromatic aberration of magnification can be effectively corrected by increasing the composite thickness of the positive lenses.

[0031] In this way, in the optical system 10, it is possible to improve the proportion (space efficiency, occupation efficiency) of the multiple lenses L21-L26 included in the second lens group G2, and to reduce the proportion of the length Lop1 of the first refractive optical system RS1 including the second lens group G2 to the total length Lop of the optical system 10. The total length Lop of the optical system 10 and the length Lop1 of the first refractive optical system RS1 may satisfy the following condition (9). 0.25 <Lop1 / Lop<0.33···(9) If the lower limit is exceeded, the correction of lateral chromatic aberration will be insufficient and the lens diameter near the intermediate image will be excessively large, whereas if the upper limit is exceeded, the overall length of the first lens group G1 will be shortened and the power will be strengthened, resulting in increased astigmatism and coma.

[0032] Depending on the application, this optical system 10 can be folded between the first refractive optical system RS1 and the second refractive optical system RS2 and / or between the first lens group G1 and the second lens group G2. For example, in the projector 1, by folding and arranging the optical system 10, it is possible to provide a compact projector that can project a wide-angle image at a short distance. In addition, by reducing the proportion of the first refractive optical system RS1 arranged closest to the screen, it is possible to provide a more compact projector 1. The total length Lop is the distance on the optical axis 7 from the surface of the enlargement side 3 of the lens L11 on the most enlargement side 3 to the surface of the reduction side 2 of the lens L49 on the most reduction side 2. The length Lop1 of the first refractive optical system RS1 is the distance on the optical axis 7 from the surface of the enlargement side 3 of the lens L11 on the most enlargement side 3 of the first refractive optical system RS1 to the intermediate image IM.

[0033] The optical system 10 includes a configuration in which, from the enlargement side 3, a first refractive optical system RS1 with positive refractive power, an intermediate image IM, and a second refractive optical system RS2 with positive refractive power are arranged. The first refractive optical system RS1 is a retrofocus type including a negative component G1f on the enlargement side 3 and a positive second lens group G2 on the reduction side 2, but the lens arrangement of the second lens group G2 is made compact as described above by ensuring positive power while suppressing overcorrection by the second lens group G2. In addition, by setting the intermediate image IM to be slightly inclined toward the enlargement side 3, the aberration correction load of the second refractive optical system RS2 is reduced, and the second refractive optical system RS2 can be configured to be suitable for high-magnification zooming.

[0034] In order to reduce the load of aberration correction on the second refractive optical system RS2, which is the second optical subsystem, it is desirable to ensure a certain degree of power for the first refractive optical system RS1, which is the first optical subsystem. The focal length (composite focal length) f1 of the first refractive optical system RS1 and the focal length (composite focal length) fw of the optical system 10 at the wide-angle end may satisfy the following condition (10). 1.0<|f1 / fw|<2.0 (10)

[0035] If the lower limit of condition (10) is exceeded, the power of the first refractive optical system RS1 becomes too strong, increasing the aberration correction load of the second refractive optical system RS2, while if the upper limit is exceeded, the power of the first refractive optical system RS1 becomes too weak, increasing the aberration correction load of the second refractive optical system RS2. The upper limit of condition (10) may be 1.7.

[0036] The first refractive optical system RS1 includes a retrofocus type power arrangement including a negative component (first component) G1f of the first lens group G1 on the enlargement side 3 and a positive second lens group G2 on the reduction side 2. Therefore, telecentricity (close to parallel to the angle that the chief ray of the most peripheral angle of view makes with the optical axis) at the position of the intermediate image IM on the reduction side 2 can be ensured. Telecentricity affects the lens diameters in front of and behind the intermediate image IM. If the telecentricity is not good, the lens diameters in front of or behind the intermediate image IM will be excessively large, increasing costs. Therefore, it is preferable that the telecentricity is good, including at the most peripheral angle of view.

[0037] The focal length fc1 of the first component G1f on the most enlarged side 3 and the focal length f1 of the first refractive optical system RS1 may satisfy the following condition (11). In addition, the focal length fw of the optical system 10 at the wide-angle end (the focal length of the entire system) may satisfy the following condition (12). 1.2<|fc1 / f1|<2.8 (11) 1.5<|fc1 / fw|<3.5···(12) If the lower limits of conditions (11) and (12) are exceeded, the power of the negative first component G1f becomes too large, and in order to ensure telecentricity, it is necessary to increase the positive power of the reduction side 2, making it difficult to correct aberrations. Conversely, if the upper limits are exceeded, the power of the negative component G1f becomes insufficient, making it difficult to ensure telecentricity.

[0038] In the second lens group G2 with positive power, a relatively strong positive lens may be arranged between the lens with positive power (lens L26 in this example) adjacent to the intermediate image IM on the enlargement side 3 and the lens with positive power (lens L24 in this example) arranged on the enlargement side 3. This configuration generates a strong under-correction field curvature. In order to correct the accompanying spherical aberration, coma aberration, and chromatic aberration, a negative lens (L25 in this example) on the enlargement side 3 with a similarly strong power may be arranged between the lenses L26 and L24. This ensures an appropriate power for under-correcting the field curvature of the first refractive optical system RS1. By under-correcting the aberration correction of the first refractive optical system (optical system on the enlargement side) RS1 and preventing the amount of under-correction from becoming excessive, the aberration load of the second refractive optical system RS2 can be reduced to provide an optical system suitable for zooming.

[0039] In addition, by using lenses with positive refractive power for the adjacent lenses facing the intermediate image IM, i.e., the lens L26 on the most reduced side 2 of the first refractive optical system RS1 and the lens L31 on the most enlarged side 3 of the second refractive optical system RS2, the telecentricity at the position of the intermediate image IM can be improved and the diameter of the lens near the intermediate image IM can be prevented from becoming excessively large, thereby reducing costs. If these adjacent lenses (L26 and L31 in this example) are arranged so that their convex surfaces face each other, the effect of improving the telecentricity can be easily obtained.

[0040] As described above, the second lens group G2 may include a lens with positive refractive power (the last lens in the group, lens L26 in this example) on the extreme reduction side 2 adjacent to the enlarged side of the intermediate image IM, and the focal length fg2e of that lens and the focal length fw of the optical system 10 at the wide-angle end may satisfy the following condition (13). 2.5<|fg2e / fw|<10.0···(13) The telecentricity on the intermediate image IM side can be kept excellent, and the generated aberration can be kept constant. The lower limit of condition (13) may be 3.0 and the upper limit may be 9.0.

[0041] In addition, the radius of curvature Rg2er of the surface of the lens on the enlargement side 3 of the intermediate image IM (the lens at the end of the group, lens L26 in this example) and the focal length fw of the optical system 10 at the wide-angle end may satisfy the following condition (14). 2.0<|Rg2er / fw|<35.0···(14) From the viewpoint of aberration correction, it is desirable that the curvature on the magnification side is large (the radius of curvature is small). If it is below the lower limit, the occurrence of spherical aberration becomes excessive, and if it is above the upper limit, it becomes difficult to maintain good telecentricity. The lower limit may be 3.0 or 4.0. The upper limit may be 30.0.

[0042] In this optical system 10, the telecentricity in the vicinity of the intermediate image IM can be set so as to satisfy the following condition (15): Angle θt is the angle that the chief ray makes with the optical axis 7 at the outermost peripheral image height in the intermediate image IM. |θt|<15.0 (15)

[0043] The second lens group G2 may include a second component (sub-lens group on the reduction side 2 of the second lens group G2) G2r consisting of a combination of positive-negative-positive refractive powers on the side closest to the intermediate image IM, i.e., on the reduction side 2. In this example, the second component G2r is composed of lenses L24, L25, and L26. The second lens group G2 may also include a lens L26 that is convex toward the reduction side 2 and has a positive refractive power, on the side closest to the intermediate image IM (reduction side 2).

[0044] In the configuration of the second component G2r, the distance LA (total length of the second component G2r) from the lens surface on the reduction side 2 of the lens (L26 in this example) adjacent to the intermediate image IM on the magnification side 3 to the lens surface on the magnification side 3 of the positive lens (L24 in this example) of the second component G2r, and the distance LB from the lens surface on the reduction side 2 of the adjacent lens L26 to the lens surface on the reduction side 2 of the negative lens (L25 in this example) on the magnification side 3 of the adjacent lens L26 may satisfy the following condition (16). 0.2 <LB / LA<0.5···(16) In order to minimize the number of lenses constituting the second component G2r while effectively correcting chromatic aberration, it is preferable to reduce the radii of curvature of the opposing surfaces of the negative and positive lens groups. To ensure the space required for this, it is preferable to satisfy the above formula.

[0045] The combination of the positive-negative lenses on the enlargement side of the second component G2r of positive-negative-positive from the enlargement side 3 has a high error sensitivity to relative decentering, and it is preferable in terms of manufacturing to have a peripheral abutment structure. Therefore, the radius of curvature Rg2m of the surface on the enlargement side 3 of the negative lens L25 adjacent on the enlargement side 3 to the lens L26 closest to the reduction side 2 of the second lens group G2, and the radius of curvature Rg2p of the surface on the reduction side 2 of the positive lens L24 adjacent on the enlargement side 3 of the negative lens L25 may satisfy the following condition (17). 0.5 <Rg2m / Rg2p<1···(17) A combination (structure) can be adopted in which the surface on the reduction side 2 of a lens L24 with a convex positive power on the reduction side 2 and the surface on the enlargement side 3 of a lens L25 with a concave negative power on the enlargement side 3 have a gentle radius of curvature on the convex side and the peripheral portion of the concave surface is abutted against each other.

[0046] As described above, the first refractive optical system RS1 is a retrofocus type, and the most enlargement side 3 includes a component (first component, subgroup) G1f with a negative power. Furthermore, it is preferable that the first component G1f includes a negative-negative power configuration from the most enlargement side 3. Furthermore, it is preferable that the first component G1f has a configuration of a negative meniscus lens L11 and a negative meniscus lens L12 from the most enlargement side 3. The second meniscus lens L12 disposed on the reduction side 2 of the first meniscus lens L11 may have at least the lens surface on the reduction side 2 formed as an aspheric surface. Furthermore, the maximum normal angle θnm of the surface on the reduction side 2 of this meniscus lens L12 may be 50 degrees or less, and the maximum normal angle θnm may be larger than the normal angle θnp of the outermost periphery. That is, the following conditions (18) and (19) may be satisfied. 40<θnm<50...(18) 0.5<θnp / θnm<1 (19) A surface that satisfies these conditions is a surface where the normal angle returns gently at the outermost periphery, making it possible to reduce the aperture of the lens on the magnification side 3 to achieve a wide angle of view, and also providing a surface that is easy to machine into an aspheric surface suitable for astigmatism correction.

[0047] The surface of the meniscus lens L11 on the most enlarged side 3 of the optical system 10 is often the largest lens surface in the optical system 10. Therefore, light rays are dispersed and pass through the lens surface. Therefore, by moving the lens L11 for focusing, it is easy to perform focus control and aberration correction. In addition, the meniscus lens L12 adjacent to the meniscus lens L11 also has a large area and is suitable for use in focusing. The lenses L11 and L12 may be moved together for focusing, or may be moved independently or in conjunction with other lenses for focusing.

[0048] The second refractive optical system RS2, which is a second optical subsystem arranged on the reduction side 2 of the intermediate image IM, is arranged on the enlargement side 3 at a third distance SP3 from the second aperture ST2, and includes a third lens group G3 having a third component (sub-lens group) G3f of negative refractive power on the enlargement side 3, and a fourth lens group G4 of positive refractive power arranged on the reduction side at a fourth distance SP4 from the second aperture ST2. The second refractive optical system RS2 is also a retrofocus lens system as a whole, with negative power arranged on the enlargement side 3 and positive power arranged on the reduction side 2, and is configured to easily ensure a long back focus while making the reduction side 2 telecentric.

[0049] The third spacing SP3 and the fourth spacing SP4 are spacings in which other lenses can be arranged, but are spacings (portions) in which no other lenses are arranged, and the third spacing SP3 and the fourth spacing SP4 at the wide-angle end, and the effective diameter SD2 of the second aperture ST2 may satisfy the following conditions (20) and (21). 0.4 <SP3 / SD2<1.5···(20) 0.4 <SP4 / SD2<1.5···(21) This makes it possible to effectively correct aberrations by avoiding fluctuations and spread of light rays (light flux) before and after the second aperture ST2, and also to suppress a decrease in the amount of light caused by the aperture ST2.

[0050] The second refractive optical system RS2 on the reduction side 2 preferably has a positive power overall and is overcorrected to match the undercorrected first refractive optical system RS1. For this reason, the lens adjacent to the intermediate image IM, i.e., the lens L31 with positive power is arranged on the most enlargement side 3 of the second refractive optical system RS2, and two lenses L32 and L33 with negative power are arranged adjacent to the reduction side 2. That is, the third component G3f of the third lens group G3 is arranged adjacent to the intermediate image IM, and includes the lens L31 with positive refractive power closest to the intermediate image and two lenses L32 and L33 with negative refractive power arranged in order from the enlargement side 3.

[0051] These two negative power lenses L32 and L33 make it possible to arrange a negative power lens group (third component) G3f on the most enlargement side 3 of the second refractive optical system RS2, thereby enabling the second refractive optical system RS2 to be arranged in a retrofocus configuration and ensuring a long back focus on the reduction side 2.

[0052] The focal length fc1 of the first component G1f of the negative power on the magnification side 3 of the first refractive optical system RS1 and the focal length fc3 of the third component G3f of the negative power on the magnification side 3 of the second refractive optical system RS2 may satisfy the following condition (22). 0.1 <fc1 / fc3<0.30···(22) If the lower limit of this condition is exceeded, it becomes difficult to ensure a sufficiently wide angle, while if the upper limit is exceeded, the lens in the vicinity of the intermediate image will have a large diameter, increasing costs.

[0053] The focal length fc1 and the focal length fc3 may satisfy the following condition (23). 0.8 <fc1 / fc3<1.2···(23) It is possible to provide an optical system 10 in which aberrations are well corrected and which has a relatively short back focus.

[0054] The third lens group G3 includes a lens L31 having a positive refractive power convex toward the enlargement side 3, which is disposed on the reduction side 2 adjacent to the intermediate image IM, at the most enlargement side 3. By disposing the lens L31 convex toward the enlargement side 3 adjacent to the intermediate image IM, the telecentricity at the position of the intermediate image IM can be improved, and the lens diameters before and after the intermediate image IM can be prevented from becoming excessively large. This makes it possible to suppress an increase in cost. In order to improve telecentricity, the adjacent lenses L26 and L31 before and after the intermediate image IM are preferably positive lenses, and further, it is preferable that the convex surfaces face each other.

[0055] As described above, in the optical system 10, the focus group is mainly arranged in the first refractive optical system RS1, and the zoom group is arranged in the second refractive optical system RS2. In the optical system 10, the intermediate image IM is inclined toward the enlargement side, so that the aberration load in each of the first refractive optical system RS1 and the second refractive optical system RS2 is reduced. Therefore, by appropriately arranging moving groups in these optical systems RS1 and RS2, high-definition zoom and focus can be achieved. The zoom group and the focus group may be arranged in either optical subsystem. Comparing the two optical subsystems of this example, that is, the first refractive optical system RS1 and the second refractive optical system RS2, as described above, the first refractive optical system RS1 is a positive group and underfocused, so that the aberration state is natural and can be designed compactly. On the other hand, the second refractive optical system RS2 is overfocused, so that the load of aberration correction is slightly larger than that of the first refractive optical system RS1. Therefore, the overall length is designed to be long, and the air space is large. Since the amount of lens movement for focusing is small and the amount of movement for zooming is large, it is preferable to mainly place the focus group in the first refractive optical system RS1 and the zoom group in the second refractive optical system RS2.

[0056] That is, the first refractive optical system RS1 includes a focus group FG including a lens that moves during focusing. The focus group FG in this example includes three focus lens groups Fg1 to Fg3 included in the first refractive optical system RS1 and a focus lens group Fg4 included in the second refractive optical system RS2. The focus group FG includes a lens with negative refractive power included in the first component G1f of the first lens group G1. Specifically, the focus group FG includes a first lens L11 with negative refractive power arranged on the most enlargement side 3 of the first lens group G1, and the first focus lens group Fg1 in this example is configured with a single first lens L11.

[0057] The focus group FG includes at least one lens included in the first refractive optical system RS1 in addition to the first lens L11. Specifically, the first refractive optical system RS1 includes a second focus lens group Fg2 including negative power lenses L12 and L13 and a positive power lens L14, and a third focus lens group Fg3 including a second lens group G2 including a first aperture ST1. The focus group FG further includes a fourth focus lens group Fg4 including a positive lens L31 on the most enlarged side 3 of the second refractive optical system RS2. With this configuration, the focus group FG includes the third focus lens group Fg3 and the fourth focus lens group Fg4 adjacent to each other in the front and rear with the intermediate image IM in between. The intermediate image IM has high telecentricity in front of and behind it, and the third and fourth focus lens groups Fg3 and Fg4 can move over a relatively large range for focusing, resulting in small fluctuations in image magnification and enabling a clearer image to be formed on the enlargement side 3 or reduction side 2.

[0058] The focus group FG may include at least one lens with positive refractive power included in the second lens group with positive power in addition to the first lens with negative power at the most enlargement side 3. The negative power and the positive power can be moved synchronously or independently for focusing, which makes it easy to correct aberrations for focusing. In the optical system 10 of this example, the entire second lens group G2 is moved for focusing as the third focus lens group Fg3. At least one focus lens group of the second lens group G2 having positive power, the focus lens group Fg3 in this example, desirably includes at least the lens L26 with positive power at the most reduction side 2 of the second lens group G2. As described above, the position of the intermediate image IM has high telecentricity, so it is easy to secure a certain amount of movement for focusing, and there is little fluctuation in image magnification during focusing.

[0059] The four focus lens groups Fg1 to Fg4 of the focus group FG may move independently and differently for focusing, or some lens groups may move synchronously. In one preferred embodiment, the lens (first lens) L11 on the most enlargement side 3, which has the largest area, and the lens (second lens) L12 adjacent to it, which has the next largest area, are set as different focus lens groups Fg1 and Fg2, and are moved differently during focusing to correct aberrations as well as focusing.

[0060] In the optical system 10, the zoom group ZG including the lens that moves during zooming is included in the second refractive optical system RS2 on the reduction side 2, which makes it easy to ensure the movement distance. A fixed group Fim may be included between the focus group FG and the zoom group ZG. The zoom group ZG includes a first zoom lens group Zg1 and a second zoom lens group Zg2 including a lens of the third lens group G3, and a third zoom lens group Zg3 and a fourth zoom lens group Zg4 including a lens of the fourth lens group G4. By distributing the zoom group ZG to the lens groups G3 and G4 in front of and behind the second aperture ST2, it is easy to ensure the movement amount and aberration correction at each zoom position is also easy.

[0061] FIG. 1(a) shows the lens arrangement at the wide-angle end of the optical system 10, and FIG. 1(b) shows the lens arrangement at the telephoto end of the optical system 10. FIG. 2 shows data of each element of the optical system 10. In FIG. 2, S is the surface number in the case of a lens, Rdy is the radius of curvature (mm) of each element (each lens surface in the case of a lens) arranged in order from the magnification side 3, Typ is the type of lens surface, SPH is a spherical surface, and ASP is an aspheric surface. d is the distance (spacing, mm) between the surfaces of each element arranged in order from the magnification side 3, H*2 is the effective diameter (diameter, mm), refractive index nd (d line), and Abbe number νd (d line) of each element. FIG. 3 shows the surface number of the aspheric surface of each element and the aspheric surface data. Aspheric surfaces are expressed by the following equation using coefficient R shown in Fig. 2 and coefficients K, A, B, C, and D shown in Fig. 3, where X is the coordinate in the optical axis direction, Y is the coordinate perpendicular to the optical axis, the light traveling direction is positive, and Rdy is the paraxial radius of curvature. Note that "en" means "10 to the power of n." The same applies to the following examples. X=(1 / Rdy)Y 2 / [1+{1-(1+K)(1 / Rdy) 2 Y 2}1 / 2] +AY 4 +BY 6 +CY 8 +DY 10

[0062] FIG. 4 shows the movement amounts of the focus lens groups Fg1 to Fg4 and the zoom lens groups Zg1 to Zg4 that move during focusing and zooming for typical states (cases) Z1 to Z6. Specifically, the distance d0 from the end (surface S1) of the enlargement side 3 to the screen (not shown) is shown by the intervals before and after each lens group at the wide-angle end (cases Z1 and Z4), the intermediate position (cases Z2 and Z5), and the telephoto end (cases Z3 and Z6) at each position of the close distance (1554.4 mm) and the far distance (6000.0 mm). Z indicates the case number, EFL indicates the composite focal length of the optical system 10 in each case Z1 to Z6, Lop indicates the total length of the optical system 10, and d0 indicates the distance to the image plane on the enlargement side 3. In this example, the movement amounts of the focus lens groups Fg1 to Fg4 and the zoom lens groups Zg1 to Zg4 are shown by intervals d2 to d57. The same applies below.

[0063] FIG. 5 shows the amount of field curvature (mm) of the intermediate image IM versus the angle of view (degrees). FIG. 6(a) and (b) show spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end. FIG. 7 and FIG. 8 show lateral aberration diagrams at each image height at the wide-angle end and the telephoto end. Note that these diagrams show wavelengths of 460 nm (dotted line), 550 nm (broken line), and 630 nm (solid line). The same applies to the following examples.

[0064] The main parameters of the optical system 10 shown in Fig. 1 are as follows. Note that the units of length, distance and interval are mm, and the same applies to the other examples below. Magnification (wide-angle end, close-up): 233.8x F-number: 2.33 (wide-angle end) / 2.43 (telephoto end) Maximum angle of view (half angle): 58.6 (wide-angle end) / 52.2 (telephoto end) Magnification ratio: 1.27 Total focal length of the entire system (close distance, wide-angle end, fw): -6.77 Total focal length of the entire system (close distance, telephoto end, ft): -8.60 The composite focal length of the first refractive optical system RS1 (close distance, f1): 8.3 The composite focal length of the second refractive optical system RS2 (Close distance, wide angle end, f2w): 120.8 The composite focal length of the second refractive optical system RS2 (close range, telephoto end, f2t): 141.4 Total length of optical system (Lop): 500.00 Total length of the first refractive optical system RS1 (Lop1): 150.85 Total length of the second refractive optical system RS2 (Lop2): 349.15 Combined focal length of the first lens group G1 (close distance, fg1): -44.89 Composite focal length of the second lens group G2 (close distance, fg2): 31.01 The composite focal length of the third lens group G3 (Close distance, wide angle end, fg3): 90.74 The composite focal length of the fourth lens group G4 (Close distance, wide angle end, fg4): 72.69 Composite focal length of the first component G1f (fc1): -10.89 The composite focal length of the third component G3f (fc3): -42.16 Focal length of the last lens in the group (fg2e): 59.7 Curvature of field of intermediate image IM (IMFc): -0.07 Petzval sum of the first lens group G1 (G1PTZ): 0.0323 Petzval sum of the second lens group G2 (G2PTZ): -0.0273 The length from the enlargement side surface to the reduction side surface of the second lens group G2 (Lg2):42.29 Total thickness of the positive power lenses in the second lens group G2 (Lg2p): 36.05 First interval (SP1): 17.00 Second interval (SP2): 15.25 Third interval (SP3): 31.20 Fourth interval (SP4): 20.30 Maximum normal angle (θnm): 46.16 Outermost periphery normal angle (θnp): 42.84 Length LA:23.11 Length LB: 11.56 Condition (1)(|G2PTZ / G1PTZ|):0.845 Condition (2)(|IMFc / f1|):0.01 Condition (3)(|IMFc / fw|):0.01 Condition (4) (SP1 / SD1:SP1 / H*2-10):0.91 Condition (5) (SP2 / SD1:SP2 / H*2-10):0.82 Condition (6)(|Sf1r / Sr1r|:|Rdy8 / Rdy12|):1.95 Condition (7)(Dg2max / Dg2min:H*2-22 / H*2-12):1.16 Condition (8)(Lg2p / Lg2):0.85 Condition (9)(Lop1 / Lop):0.30 Condition (10)(|f1 / fw|):1.23 Condition (11)(|fc1 / f1|):1.31 Condition (12)(|fc1 / fw|):1.61 Condition (13)(|fg2e / fw|):8.82 Condition (14)(|Rg2er / fw|:|Rdy22 / fw|):4.40 Condition (15)(|θt|):0.10 Condition(16)(LB / LA):0.50 Condition (17) (Rg2m / Rg2p:Rdy20 / Rdy19):0.99 Condition (18)(θnm):46.16 Condition (19) (θnp / θnm): 0.93 Condition(20)(SP3 / SD2:SP3 / H*2-40):1.00 Condition (21)(SP4 / SD2:SP4 / H*2-40):0.65 Condition(22)(fc1 / fc3):0.26

[0065] In this optical system 10, all of the above conditions (1) to (22) are satisfied, and focusing is mainly performed by the lens group arranged in the first refractive optical system RS1 on the enlargement side 3 of the intermediate image IM, and zooming can be performed by the lens group arranged in the second refractive optical system RS2 on the reduction side 2. Furthermore, both the first refractive optical system RS1 and the second refractive optical system RS2 are retrofocus types with negative power arranged on the enlargement side 3, and the vicinity of the intermediate image IM and the reduction side 2 can be made telecentric. By making the vicinity of the intermediate image IM telecentric, it is possible to suppress an increase in the diameter of the lens arranged in the middle. Furthermore, by tilting the intermediate image IM toward the enlargement side 3, it is possible to appropriately set the positive power of the second lens group G2, and it is possible to realize a compact arrangement in which many lenses are closely packed in the second lens group G2. Therefore, it is possible to provide an optical system 10 that can be made compact as a whole.

[0066] In particular, this optical system 10 is designed to have a very long back focus and a small image circle, and is suitable for applications that require high magnification and combination with an illumination system, etc. As shown in the aberration diagram, this optical system 10 also provides good aberration correction during zooming and focusing, and as a projection optical system, it is possible to provide a projection optical system 10 that is capable of zooming and is compact yet capable of projecting an image with good aberration correction, and a projector 1 equipped with the projection optical system 10.

[0067] Fig. 9 shows several different examples of the focus group FG. Fig. 9(a) shows an example in which the first lens group G1 is divided into two groups for focusing. That is, the first focus lens group Fg1 is made up of the lens L11 of the first lens group G1, and the other lenses L12 to L14 make up the second focus lens group Fg2, and focusing is performed by these two lens groups Fg1 and Fg2.

[0068] 9(b) shows an example in which focusing is performed by dividing the first lens group G1 into three groups. That is, the first focus lens group Fg1 is made up of lens L11 of the first lens group G1, the second focus lens group Fg2 is made up of lenses L12 and L13, and the third focus lens group Fg3 is made up of lens L14, and focusing is performed by these three lens groups Fg1 to Fg3.

[0069] 9(c) shows an example in which the second lens group G2 is also moved during focusing. That is, the lens L11 of the first lens group G1 constitutes the first focus lens group Fg1, the lenses L12 to L14 constitute the second focus lens group Fg2, and the second lens group L21 to L26 constitute the third focus lens group Fg3, and focusing is performed using these three lens groups Fg1 to Fg3.

[0070] 9(d) shows an example in which some of the lenses in the second lens group G2 are moved during focusing. That is, the first focus lens group Fg1 is made up of the lens L11 in the first lens group G1, the second focus lens group Fg2 is made up of the lenses L12 to L14, and the third focus lens group Fg3 is made up of the lens L26 in the second lens group G2 that is closest to the intermediate image IM, and focusing is performed by these three lens groups Fg1 to Fg3.

[0071] 9(e) is an example in which, in addition to a part of the second lens group G2, the lenses of the third lens group G3 are moved during focusing. That is, the first focus lens group Fg1 is composed of the lens L11 of the first lens group G1, the second focus lens group Fg2 is composed of the lenses L12 to L14, the third focus lens group Fg3 is composed of the lens L26 of the second lens group G2 that is closest to the intermediate image IM, and the fourth focus lens group Fig. 4 is composed of the lens L31 of the third lens group G3 that is closest to the intermediate image IM, and focusing is performed by these four lens groups Fg1 to Fg4.

[0072] 9(f) shows an example in which focusing is performed by the first lens group G1 as a whole. That is, the first focus lens group Fg1 is made up of the lenses L11-L14 of the first lens group G1, the third focus lens group Fg2 is made up of the lens L26 of the second lens group G2 that is closest to the intermediate image IM, and the third focus lens group Fig3 is made up of the lens L31 of the third lens group G3 that is closest to the intermediate image IM, and focusing is performed by these three lens groups Fg1-Fg3.

[0073] Although the configuration of the focus group FG is not limited to this, in the optical system 10, the two lenses L11 and L12 on the most magnified side 3, which have the largest area through which light rays pass, are moved cooperatively, i.e., independently or synchronously, during focusing, whereby the light rays can be efficiently controlled and good focusing performance can be obtained.

[0074] Another example of a projector is shown in FIG. 10. This projector 1 also includes an optical system 10 that projects from an image surface (first image surface) 5a of an optical modulator (light valve) 5 on the reduction side 2 onto a screen or wall surface on the enlargement side 3. As in the above embodiment, this optical system 10 may be an optical system for an imaging device 21. The following will also be described using an optical system 10 for projection as an example. This optical system 10 is composed of a total of 23 lenses, and includes a first optical subsystem (first refractive optical system) RS1 including a plurality of lenses arranged on the enlargement side 3, and a second optical subsystem (second refractive optical system) RS2 including a plurality of lenses arranged on the reduction side 2 with an intermediate image IM in between, and the intermediate image IM formed by the second refractive optical system RS2 is enlarged and projected onto a screen or the like by the wide-angle first refractive optical system RS1.

[0075] The first refractive optical system RS1 includes a first lens group G1, which is disposed on the enlargement side (enlargement conjugate side) 3 with a first space SP1 at which other lenses can be arranged but no other lenses are arranged, and has a first component (sub-lens group) G1f of negative refractive power on the enlargement side 3, and a second lens group G2, which is disposed on the reduction side (reduction conjugate side) 2 with a second space SP2 at which other lenses can be arranged but no other lenses are arranged, and has a positive refractive power (composite refractive power) with the reduction side 2 adjacent to the intermediate image IM, with the first lens group G1 being composed of four lenses L11 to L14, and the second lens group G2 being composed of five lenses L21 to L25.

[0076] The basic configuration of the first lens group G1 is the same as that of the optical system 10 shown in FIG. 1, and has a negative-negative-negative-positive power arrangement. Since the positive power of the lens L14 is set to be strong, the focal length fg1 of the entire first lens group G1 is slightly positive. The second lens group G2 includes, from the enlargement side 3, lenses L21 and L22 having a positive-negative power arrangement, and lenses L23 to L25 having a positive-negative-positive power arrangement, and the lenses L23 to L25 form a second component (second sub-lens group) G2r. The second lens group G2 includes, from the enlargement side 3, a biconvex positive lens L21, a negative meniscus lens L22 convex to the reduction side 2, a biconvex positive lens L23, a biconcave negative lens L24, and a biconvex positive lens L25. The lens at the end of the group in this embodiment is the positive lens L25.

[0077] The second refractive optical system RS2 includes a third lens group G3 having a third component (sub lens group) G3f of negative refractive power on the enlargement side and disposed on the enlargement side 3 with a third space SP3 from the second aperture ST2, and a fourth lens group G4 having positive refractive power disposed on the reduction side 2 with a fourth space SP4 from the second aperture ST2. The third lens group G3 is composed of seven lenses L31 to L37, and the fourth lens group G4 is composed of seven lenses L41 to L47.

[0078] The specific power arrangement of the third lens group G3 is the same as that of the optical system 10 shown in Fig. 1. The third lens group G3 includes, from the enlargement side 3, a positive meniscus lens L31 convex toward the reduction side 2, a biconcave negative lens L32, a negative meniscus lens L33 convex toward the enlargement side 3, a biconcave negative lens L34, and biconvex positive lenses L35 to L37. The fourth lens group G4 includes, from the enlargement side 3, negative-positive-negative-positive-negative-positive-positive lenses L41 to L47. The fourth lens group G4 includes, from the enlargement side 3, a negative meniscus lens L41 convex toward the enlargement side 3, a biconvex positive lens L42, a biconcave negative lens L43, a biconvex positive lens L44, a negative meniscus lens L45 convex toward the reduction side 2, a positive meniscus lens L46 convex toward the reduction side 2, and a biconvex positive lens L47. That is, this is the same as the configuration in which the two lenses on the enlargement side 3 of the fourth lens group G4 of the optical system 10 shown in FIG. 1 are omitted.

[0079] This optical system 10 includes three focus lens groups Fg1-Fg3 arranged on the enlargement side 3 relative to intermediate fixed lens groups Fim1 and Fim2, four zoom lens groups Zg1-Zg4 arranged on the reduction side 2, and further includes a terminal fixed lens group Fie on the extreme reduction side 2. The zoom lens groups Zg1-Zg4 move during zooming (variable magnification) and vary in distance to an image surface, for example, image surface 25a on the reduction side 2. The focus lens groups Fg1-Fg3 do not move during zooming (variable magnification), but move during focusing (focusing). The fixed lens groups Fim1, Fim2, and Fie do not move in any case.

[0080] The optical system 10 of this example performs focusing by dividing the first lens group G1 into three and moving them independently. That is, the first focus lens group Fg1 is composed of a single lens L11 with negative power on the most enlargement side 3 of the first lens group G1, the second focus lens group Fg2 is composed of lenses L12 and L13 with negative-negative power of the first lens group G1, and the third focus lens group Fg3 is composed of a lens L14 with positive power.

[0081] The second lens group G2 and the lens group G3f on the enlargement side 3 of the third lens G3 do not move during focusing and zooming. In other words, the lens groups disposed in front of and behind the intermediate image IM do not move during focusing and zooming, and the intermediate image IM does not move or moves very little, making it possible to provide an optical system 10 in which the fluctuation in optical performance due to focusing and zooming is small.

[0082] The zoom group ZG includes four zoom lens groups. The first zoom lens group Zg1 is composed of the negative-positive power lenses L34 and L35 of the third lens group G3, the second zoom lens group Zg2 is composed of the positive power lens L36 of the third lens group G3, and the third zoom lens group Zg3 is composed of the positive power lens L37 of the third lens group G3 on the most reduction side 2. The fourth zoom lens group Zg4 is composed of the negative-positive-negative-positive-negative-positive lenses L41 to L46 of the fourth lens group G4 including the second aperture ST2. The final fixed lens group Fie is composed of the positive power lens L47 of the fourth lens group G4 on the most reduction side 2.

[0083] In this optical system 10, the first refractive optical system RS1 and the second refractive optical system RS2 are of a retrofocus type in which the components G1f and G3f, which have negative refractive power, are arranged on the magnification side (magnification conjugate side) 3, respectively, and an optical system can be obtained in which the magnification side 3 has a large wide angle of view and the reduction side 2 has a long back focus and is telecentric or close to it. Furthermore, the intermediate image IM is designed to be formed so as to be inclined toward the magnification side 3. Therefore, as with the optical system 10 shown in FIG. 1, the change in lens diameter can be reduced, and multiple lenses can be arranged compactly in a close relationship. Therefore, it is possible to provide an optical system 10 that is compact and can well correct aberrations. Other specific configurations are common to the optical system 10 shown in FIG. 1.

[0084] FIG. 10(a) shows the lens arrangement at the wide-angle end of the optical system 10, and FIG. 10(b) shows the lens arrangement at the telephoto end of the optical system 10. FIG. 11 shows data of each element of the optical system 10. FIG. 12 shows the aspheric surface number and aspheric surface data of each element. FIG. 13 shows the movement amount of the focus lens group and the zoom lens group that move during focusing and zooming, in terms of the front and rear spacing of each lens group at the wide-angle end (Z1, Z4), the intermediate position (Z2, Z5), and the telephoto end (Z3, Z6) when the distance d0 from the end (surface S1) of the enlargement side 3 to the screen (not shown) is close (3400 mm) and far (12000 mm, 12 m).

[0085] Fig. 14 shows the amount of field curvature (mm) of the intermediate image IM versus the angle of view (degrees). Fig. 15(a) and (b) show the spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end. Fig. 16 and Fig. 17 show the lateral aberration diagrams at each image height at the wide-angle end and the telephoto end.

[0086] The main parameters of the optical system 10 shown in FIG. Magnification (wide-angle end, close-up): 217.4 F-number: 2.37 (wide-angle end) / 2.44 (telephoto end) Maximum angle of view (half angle): 54.8 (wide-angle end) / 49.5 (telephoto end) Magnification ratio: 1.21 Total focal length of the entire system (close distance, wide-angle end, fw): -15.87 Total focal length of the entire system (close distance, telephoto end, ft): -19.20 Composite focal length of the first refractive optical system RS1 (close distance, f1): 16.0 The composite focal length of the second refractive optical system RS2 (Close distance, wide-angle end, f2w): 213.6 The composite focal length of the second refractive optical system RS2 (close range, telephoto end, f2t): 267.6 Total length of optical system (Lop): 900.00 Total length of the first refractive optical system RS1 (Lop1): 283.97 Total length of the second refractive optical system RS2 (Lop2): 616.03 Composite focal length of the first lens group G1 (close distance, fg1): 131.65 Composite focal length of the second lens group G2 (close distance, fg2): 68.45 The composite focal length of the third lens group G3 (Close distance, wide angle end, fg3): 135.86 The composite focal length of the fourth lens group G4 (close distance, wide angle end, fg4): 127.29 Composite focal length of the first component G1f (fc1): -19.76 The composite focal length of the third component G3f (fc3): -160.25 Focal length of the last lens in the group (fg2e): 48.8 Curvature of field of intermediate image IM (IMFc): -21.35 Petzval sum of the first lens group G1 (G1PTZ): 0.0171 Petzval sum of the second lens group G2 (G2PTZ): -0.0122 The length from the enlargement side surface to the reduction side surface of the second lens group G2 (Lg2):60.85 Total thickness of the positive power lenses in the second lens group G2 (Lg2p): 41.43 First interval (SP1): 30.25 Second interval (SP2): 30.25 Third interval (SP3): 62.07 Fourth interval (SP4): 40.44 Maximum normal angle (θnm): 43.03 Outermost periphery normal angle (θnp): 30.53 Length LA:40.52 Length LB:18.50 Condition (1)(|G2PTZ / G1PTZ|):0.71 Condition (2)(|IMFc / f1|):1.33 Condition (3)(|IMFc / fw|):1.35 Condition (4) (SP1 / SD1:SP1 / H*2-10): 0.69 Condition (5) (SP2 / SD1:SP2 / H*2-10): 0.69 Condition (6) (|Sf1r / Sr1r|:|Rdy8 / Rdy12|): 0.19 Condition (7) (Dg2max / Dg2min:H*2-21 / H*2-12):1.11 Condition (8) (Lg2p / Lg2): 0.68 Condition (9) (Lop1 / Lop): 0.32 Condition (10) (|f1 / fw|): 1.01 Condition (11) (|fc1 / f1|): 1.24 Condition (12) (|fc1 / fw|): 1.25 Condition (13) (|fg2e / fw|): 3.07 Condition (14) (|Rg2er / fw|:|Rdy20 / fw|):2.59 Condition (15) (|θt|): 1.01 Condition (16) (LB / LA): 0.46 Condition (17) (Rg2m / Rg2p:Rdy18 / Rdy17): 1.01 Condition (18) (θnm): 43.03 Condition (19) (θnp / θnm): 0.71 Condition (20) (SP3 / SD2:SP3 / H*2-39):1.15 Condition (21) (SP4 / SD2:SP4 / H*2-39): 0.75 Condition (22) (fc1 / fc3): 0.12

[0087] Of the above conditions (1) to (22), this optical system 10 does not take into consideration condition (17) during design, but satisfies all of the other conditions. This optical system 10 also performs focusing mainly by the lens group arranged in the first refractive optical system RS1 on the enlargement side 3 of the intermediate image IM, and can perform zooming by the lens group arranged in the second refractive optical system RS2 on the reduction side 2. In addition, by realizing a compact arrangement in which many lenses are closely packed in the second lens group G2, it is possible to provide an optical system 10 that can be made compact overall.

[0088] This optical system 10 is designed to have a very long back focus and a large image circle. In addition, the focusing distance is very wide, ranging from 3.4 m to 12 m. Therefore, it is suitable for applications such as long-distance projection in combination with an illumination system. As shown in the aberration diagram, this optical system 10 also has good aberration correction during zooming and focusing, and as a projection optical system, it is possible to provide a projection optical system 10 that is capable of zooming and is compact yet capable of projecting an image with good aberration correction, and a projector 1 equipped with the projection optical system 10.

[0089] Another example of a projector is shown in Fig. 18. This projector 1 also includes an optical system 10 that projects from an image surface (first image surface) 5a of an optical modulator (light valve) 5 on the reduction side 2 onto a screen or wall surface on the enlargement side 3. As in the above embodiment, this optical system 10 may be an optical system for an imaging device 21. This optical system 10 is composed of a total of 24 lenses, and includes a first optical subsystem (first refractive optical system) RS1 including a plurality of lenses arranged on the enlargement side 3, and a second optical subsystem (second refractive optical system) RS2 including a plurality of lenses arranged on the reduction side 2 with an intermediate image IM in between, and the intermediate image IM formed by the second refractive optical system RS2 is enlarged and projected onto a screen or the like by the wide-angle first refractive optical system RS1.

[0090] The first refractive optical system RS1 includes a first lens group G1 arranged on the magnification side (magnification conjugate side) 3 with a first interval SP1 from the first aperture ST1, the first lens group G1 having a first component (sub-lens group) G1f of negative refractive power on the magnification side 3, and a second lens group G2 arranged on the reduction side (reduction conjugate side) 2 with a second interval SP2 from the first aperture ST1, the reduction side 2 being adjacent to the intermediate image IM and having positive refractive power (composite refractive power). The first lens group G1 is composed of two lenses, L11 and L12, and the second lens group G2 is composed of five lenses, L21 to L25.

[0091] The first lens group G1 is composed of a negative first component G1f. The negative first component G1f has a negative-negative power arrangement and includes negative meniscus lenses L11 and L12 that are convex on the enlargement side 3. The second lens group G2 includes lenses L21 and L22 that have a positive-positive power arrangement from the enlargement side 3, and lenses L23 to L25 that have a positive-negative-positive power arrangement, and the lenses L22 to L25 constitute a second component (second sub-lens group) G2r. The second lens group G2 includes, from the enlargement side 3, a positive meniscus lens L21 that is convex on the reduction side 2, a biconvex positive lens L22, a biconvex positive lens L23, a biconcave negative lens L24, and a biconvex positive lens L25. The lens at the end of the group in this embodiment is the positive lens L25.

[0092] The second refractive optical system RS2 includes a third lens group G3 having a third component (sub lens group) G3f of negative refractive power on the enlargement side and disposed on the enlargement side at a third distance SP3 from the second aperture ST2, and a fourth lens group G4 having positive refractive power disposed on the reduction side 2 at a fourth distance SP4 from the second aperture ST2. The third lens group G3 is composed of six lenses L31 to L36, and the fourth lens group G4 is composed of eleven lenses L41 to L51.

[0093] The third lens group G3 includes a negative third component G3f including positive-negative-negative lenses L31 to L33, and negative-positive lenses L34 and L35. The third lens group G3 includes, from the magnification side 3, a positive meniscus lens L31 convex toward the magnification side 3, a negative meniscus lens L32 convex toward the magnification side 3, biconcave negative lenses L33 and L34, a biconvex positive lens L35, and a positive lens L36 convex toward the magnification side 3.

[0094] The fourth lens group G4 includes positive-negative-positive-negative-positive-negative-positive-negative-positive lenses L41 to L51 from the enlargement side 3. The fourth lens group G4 includes, from the enlargement side 3, a positive meniscus lens L41 convex toward the reduction side 2, a biconcave negative lens L42, a biconvex positive lens L43, a negative meniscus lens L44 convex toward the enlargement side 3, a biconvex positive lens L45, a biconcave negative lens L46, a biconvex positive lens L47, a biconcave negative lens L48, a biconvex positive lens L49, a biconcave negative lens L50, and a biconvex positive lens L51. That is, the fourth lens group G4 of the optical system 10 shown in FIG. 2 has a configuration in which a positive-negative-positive power is added to the enlargement side 3, and the reduction side 2 is made negative-positive.

[0095] This optical system 10 does not have an intermediate fixed lens group, but includes three focus lens groups Fg1-Fg3 arranged on the enlargement side 3 of an intermediate image IM, four zoom lens groups Zg1-Zg4 arranged on the reduction side 2, and further includes a terminal fixed lens group Fie on the extreme reduction side 2. The zoom lens groups Zg1-Zg4 move during zooming (variable magnification), and the distance to an image surface, for example, image surface 25a on the reduction side 2, varies. The focus lens groups Fg1-Fg3 do not move during zooming (variable magnification), but move during focusing (focusing).

[0096] In the optical system 10 of this example, focusing is performed by dividing the second lens group G2 into two and moving them independently. That is, the first focus lens group Fg1 is composed of the first lens group G1, the second focus lens group Fg2 is composed of the positive-positive-positive-negative lenses L21 to L24 of the second lens group G2, and the third focus lens group Fg3 is composed of the lens L25 with positive power.

[0097] The zoom group ZG includes four zoom lens groups. The first zoom lens group Zg1 is composed of the lenses L31-L33 of the third negative component G3f of the third lens group G3, the second zoom lens group Zg2 is composed of the negative-positive lenses L34 and L35 of the third lens group G3 and the lens L36 of the third lens group G3 with positive power, and the fourth zoom lens group Zg4 is composed of the positive-negative-positive-negative-positive-negative-positive-negative-positive lenses L41-L49 of the fourth lens group G4 including the second aperture ST2. The final fixed lens group Fie is composed of the lenses L50 and L51 of the fourth lens group G4 with negative-positive power on the most reduction side 2.

[0098] In this optical system 10, the first refractive optical system RS1 and the second refractive optical system RS2 are of a retrofocus type in which the components G1f and G3f, which have negative refractive power, are arranged on the magnification side (magnification conjugate side) 3, respectively, and an optical system can be obtained in which the magnification side 3 has a large wide angle of view and the reduction side 2 has a long back focus and is telecentric or close to it. Furthermore, the intermediate image IM is designed to be formed so as to be inclined toward the magnification side 3. Therefore, as with the optical system 10 shown in FIG. 1, the change in lens diameter can be reduced, and multiple lenses can be arranged compactly in a close relationship. Therefore, it is possible to provide an optical system 10 that is compact and can well correct aberrations. Other specific configurations are common to the optical system 10 shown in FIG. 1.

[0099] FIG. 18(a) shows the lens arrangement at the wide-angle end of the optical system 10, and FIG. 18(b) shows the lens arrangement at the telephoto end of the optical system 10. FIG. 19 shows the data of each element of the optical system 10. FIG. 20 shows the aspheric surface number and aspheric surface data of each element. FIG. 21(a) shows the movement amount of the zoom lens group that moves during zooming by the front and rear spacing of each lens group at the wide-angle end (Z1) where the distance d0 from the end (surface S1) of the enlargement side 3 to the screen (not shown) is close (1625 mm), the intermediate position (Z2), and the telephoto end (Z3). FIG. 21(b) shows the movement amount of the focus lens group that moves during focusing at close distance (1625 mm, Z10) and long distance (3000 mm, Z20).

[0100] Fig. 22 shows the amount of field curvature (mm) of the intermediate image IM versus the angle of view (degrees). Fig. 23(a) and (b) show the spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end. Fig. 24 and Fig. 25 show the lateral aberration diagrams at each image height at the wide-angle end and the telephoto end.

[0101] The main parameters of the optical system 10 shown in FIG. Magnification (wide-angle end, close-up): 156.0 F-number: 1.89 (wide-angle end) / 2.05 (telephoto end) Maximum angle of view (half angle): 58.7 (wide-angle end) / 54.5 (telephoto end) Magnification ratio: 1.18 Total focal length of the entire system (close distance, wide-angle end, fw): -10.58 Total focal length of the entire system (close distance, telephoto end, ft): -12.48 The composite focal length of the first refractive optical system RS1 (close distance, f1): 17.4 The composite focal length of the second refractive optical system RS2 (Close distance, wide-angle end, f2w): 50.95 The composite focal length of the second refractive optical system RS2 (close range, telephoto end, f2t): 56.2 Total length of optical system (Lop): 500.00 Total length of the first refractive optical system RS1 (Lop1): 151.93 Total length of the second refractive optical system RS2 (Lop2): 348.07 Composite focal length of the first lens group G1 (close distance, fg1): -30.92 Composite focal length of the second lens group G2 (close distance, fg2): 30.07 The composite focal length of the third lens group G3 (Close distance, wide angle end, fg3): 95.67 The composite focal length of the fourth lens group G4 (Close distance, wide angle end, fg4): 52.98 Composite focal length of the first component G1f (fc1): -30.92 The composite focal length of the third component G3f (fc3): -37.92 Focal length of the last lens in the group (fg2e): 60.9 Curvature of field of intermediate image IM (IMFc): -3.46 Petzval sum of the first lens group G1 (G1PTZ): 0.0195 Petzval sum of the second lens group G2 (G2PTZ): -0.0236 The length from the enlargement side surface to the reduction side surface of the second lens group G2 (Lg2):70.89 Total thickness of the positive power lenses in the second lens group G2 (Lg2p): 59.79 First interval (SP1): 27.48 Second interval (SP2): 15.28 Third interval (SP3): 20.80 Fourth interval (SP4): 24.33 Maximum normal angle (θnm): 42.86 Outermost periphery normal angle (θnp): 33.84 Length LA:45.30 Length LB:22.74 Condition (1)(|G2PTZ / G1PTZ|):1.21 Condition (2)(|IMFc / f1|):0.20 Condition (3)(|IMFc / fw|):0.33 Condition (4)(SP1 / SD1:SP1 / H*2-6):1.31 Condition (5) (SP2 / SD1:SP2 / H*2-6):0.73 Condition (6)(|Sf1r / Sr1r|:|Rdy4 / Rdy8|):0.18 Condition (7)(Dg2max / Dg2min:H*2-17 / H*2-8):1.55 Condition (8)(Lg2p / Lg2):0.84 Condition (9)(Lop1 / Lop):0.30 Condition (10)(|f1 / fw|):1.64 Condition (11)(|fc1 / f1|):1.78 Condition (12)(|fc1 / fw|):2.92 Condition (13)(|fg2e / fw|):5.76 Condition (14)(|Rg2er / fw|:|Rdy16 / fw|):5.11 Condition (15)(|θt|):6.08 Condition(16)(LB / LA):0.50 Condition (17)(Rg2m / Rg2p:Rdy14 / Rdy13):0.99 Condition (18)(θnm):42.86 Condition (19) (θnp / θnm): 0.79 Condition(20)(SP3 / SD2:SP3 / H*2-33):0.47 Condition(21)(SP4 / SD2:SP4 / H*2-33):0.54 Condition (23)(fc1 / fc3):0.82

[0102] This optical system 10 satisfies all of the above conditions (1) to (21) and (23). This optical system 10 also performs focusing mainly by the lens group arranged in the first refractive optical system RS1 on the enlargement side 3 of the intermediate image IM, and zooming by the lens group arranged in the second refractive optical system RS2 on the reduction side 2. Furthermore, by realizing a compact arrangement in which many lenses are closely packed in the second lens group G2, the optical system can be made compact overall, and an optical system 10 with a small F-number and a bright image can be provided.

[0103] This optical system 10 is designed to have a relatively short back focus and a large image circle. In addition, the intermediate image IM is enlarged and formed. Therefore, it is suitable for applications that do not require a large back focus. As shown in the aberration diagram, this optical system 10 also has good aberration correction during zooming and focusing, and as a projection optical system, it is possible to provide a projection optical system 10 that is capable of zooming and is compact yet capable of projecting an image with good aberration correction, and a projector 1 equipped with the projection optical system 10.

[0104] Another example of a projector is shown in Fig. 26. This projector 1 also includes an optical system 10 that projects from an image surface (first image surface) 5a of an optical modulator (light valve) 5 on the reduction side 2 onto a screen or wall surface on the enlargement side 3. This optical system 10 is composed of a total of 26 lenses, and includes a first optical subsystem (first refractive optical system) RS1 including a plurality of lenses arranged on the enlargement side 3, and a second optical subsystem (second refractive optical system) RS2 including a plurality of lenses arranged on the reduction side 2 with an intermediate image IM in between, and the intermediate image IM formed by the second refractive optical system RS2 is enlarged and projected onto a screen or the like by the wide-angle first refractive optical system RS1.

[0105] The first refractive optical system RS1 includes a first lens group G1 arranged on the enlargement side (enlargement conjugate side) 3 with a first interval SP1 from the first aperture ST1, the first lens group G1 having a first component (sub lens group) G1f of negative refractive power on the enlargement side 3, and a second lens group G2 arranged on the reduction side (reduction conjugate side) 2 with a second interval SP2 from the first aperture ST1, the reduction side 2 being adjacent to the intermediate image IM and having a positive refractive power (composite refractive power). In this optical system 10, the configurations of the first lens group G1 and the second lens group G2 are common to those of the optical system 10 shown in FIG.

[0106] The second refractive optical system RS2 includes a third lens group G3 having a third component (sub lens group) G3f of negative refractive power on the enlargement side and disposed on the enlargement side 3 with a third spacing SP3 from the second aperture ST2, and a fourth lens group G4 having positive refractive power disposed on the reduction side 2 with a fourth spacing SP4 from the second aperture ST2. The third lens group G3 is composed of eight lenses L31 to L38, and the fourth lens group G4 is composed of eleven lenses L41 to L51.

[0107] The third lens group G3 includes a negative third component G3f including positive-negative-negative lenses L31 to L33, and negative-positive-positive-negative-positive lenses L34 to L38. The third lens group G3 includes, from the enlargement side 3, a positive meniscus lens L31 convex toward the enlargement side 3, biconcave negative lenses L32 and L33, a negative meniscus lens L34 convex toward the reduction side 2, a positive meniscus lens L35 convex toward the reduction side 2, a biconvex positive lens L36, a negative meniscus lens L37 convex toward the reduction side 2, and a positive meniscus lens L38 convex toward the enlargement side 3.

[0108] 18, the fourth lens group G4 includes positive-negative-positive-negative-positive-negative-positive-negative-positive-negative-positive lenses L41-L51 from the magnification side 3. The fourth lens group G4 has a basic configuration in common with the optical system 10 shown in FIG 18, except that the lens L41 closest to the magnification side 3 is a biconvex positive lens.

[0109] This optical system 10 does not have an intermediate fixed lens group, but includes three focus lens groups Fg1 to Fg3 arranged on the enlargement side 3 of the intermediate image IM, and four zoom lens groups Zg1 to Zg4 arranged on the reduction side 2, and further includes a terminal fixed lens group Fie on the extreme reduction side 2.

[0110] In the optical system 10 of this example, focusing is performed by dividing the first lens group G1 into two and moving them independently. That is, the first focus lens group Fg1 is composed of the lens L11 of the first lens group G1, the second focus lens group Fg2 is composed of the lens L12 of the first lens group G1, and the third focus lens group Fg3 is composed of the positive-positive-positive-negative-positive lenses L21 to L25 of the second lens group G2 including the first aperture ST1.

[0111] The zoom group ZG includes four zoom lens groups. The first zoom lens group Zg1 is composed of the lenses L31-L33 of the third negative component G3f of the third lens group G3 and the lens L34. The second zoom lens group Zg2 is composed of the positive-positive-negative lenses L35, L36 and L37 of the third lens group G3 and the positive power lens L38 of the third lens group G3. The fourth zoom lens group Zg4 is composed of the positive-negative-positive-negative-positive-negative-positive-negative-positive lenses L41-L49 of the fourth lens group G4 including the second aperture ST2. The final fixed lens group Fie is composed of the negative-positive power lenses L50 and L51 of the fourth lens group G4 on the most reduction side 2.

[0112] In this optical system 10, the first refractive optical system RS1 and the second refractive optical system RS2 are of a retrofocus type in which the components G1f and G3f, which have negative refractive power, are arranged on the magnification side (magnification conjugate side) 3, respectively, and an optical system can be obtained in which the magnification side 3 has a large wide angle of view and the reduction side 2 has a long back focus and is telecentric or close to it. Furthermore, the intermediate image IM is designed to be formed so as to be inclined toward the magnification side 3. Therefore, as with the optical system 10 shown in FIG. 1, the change in lens diameter can be reduced, and multiple lenses can be arranged compactly in a close relationship. Therefore, it is possible to provide an optical system 10 that is compact and can well correct aberrations. Other specific configurations are common to the optical system 10 shown in FIG. 1.

[0113] FIG. 26(a) shows the lens arrangement at the wide-angle end of the optical system 10, and FIG. 26(b) shows the lens arrangement at the telephoto end of the optical system 10. FIG. 27 shows the data of each element of the optical system 10. FIG. 28 shows the aspheric surface number and aspheric surface data of each element. FIG. 29(a) shows the movement amount of the zoom lens group that moves during zooming by the front and rear spacing of each lens group at the wide-angle end (Z1) where the distance d0 from the end (surface S1) of the enlargement side 3 to the screen (not shown) is close (1625 mm), the intermediate position (Z2), and the telephoto end (Z3). FIG. 29(b) shows the movement amount of the focus lens group that moves during focusing at close distance (1625 mm, Z10) and long distance (3000 mm, Z20).

[0114] Fig. 30 shows the amount of field curvature (mm) of the intermediate image IM versus the angle of view (degrees). Fig. 31(a) and (b) show the spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end. Fig. 32 and Fig. 33 show the lateral aberration diagrams at each image height at the wide-angle end and the telephoto end.

[0115] The main parameters of the optical system 10 shown in FIG. 26 are as follows: Magnification (wide-angle end, close-up): 156.7 F-number: 1.99 (wide-angle end) / 2.10 (telephoto end) Maximum angle of view (half angle): 58.7 (wide-angle end) / 54.3 (telephoto end) Image circle (reduced side): φ35.0 Back Focus (reduced side): 48.0 Magnification ratio: 1.18 Total focal length of the entire system (close distance, wide-angle end, fw): -10.56 Total focal length of the entire system (close distance, telephoto end, ft): -12.46 Composite focal length of the first refractive optical system RS1 (close distance, f1): 12.1 The composite focal length of the second refractive optical system RS2 (Close distance, wide-angle end, f2w): 69.6 The composite focal length of the second refractive optical system RS2 (close range, telephoto end, f2t): 81.5 Total length of optical system (Lop): 500.00 Total length of the first refractive optical system RS1 (Lop1): 150.85 Total length of the second refractive optical system RS2 (Lop2): 349.15 Composite focal length of the first lens group G1 (close distance, fg1): -32.34 Combined focal length of the second lens group G2 (close distance, fg2): 28.11 The composite focal length of the third lens group G3 (Close distance, wide angle end, fg3): 81.37 The composite focal length of the fourth lens group G4 (Close distance, wide angle end, fg4): 91.20 Composite focal length of the first component G1f (fc1): -32.34 The composite focal length of the third component G3f (fc3): -30.89 Focal length of the last lens in the group (fg2e): 44.9 Curvature of field of intermediate image IM (IMFc): -1.66 Petzval sum of the first lens group G1 (G1PTZ): 0.0170 Petzval sum of the second lens group G2 (G2PTZ): -0.0274 The length from the enlargement side surface to the reduction side surface of the second lens group G2 (Lg2):54.98 Total thickness of the positive power lenses in the second lens group G2 (Lg2p): 51.49 First interval (SP1): 37.6 Second interval (SP2): 14.66 Third interval (SP3): 20.80 Fourth interval (SP4): 20.35 Maximum normal angle (θnm): 44.85 Outermost periphery normal angle (θnp): 42.59 Length LA:32.7 Length LB: 11.50 Condition (1)(|G2PTZ / G1PTZ|):1.61 Condition (2)(|IMFc / f1|):0.14 Condition (3) (|IMFc / fw|): 0.16 Condition (4) (SP1 / SD1:SP1 / H*2-6): 1.63 Condition (5) (SP2 / SD1:SP2 / H*2-6): 0.64 Condition (6) (|Sf1r / Sr1r|:|Rdy4 / Rdy8|): 0.26 Condition (7) (Dg2max / Dg2min:H*2-11 / H*2-8):1.34 Condition (8) (Lg2p / Lg2): 0.94 Condition (9) (Lop1 / Lop): 0.30 Condition (10) (|f1 / fw|): 1.15 Condition (11) (|fc1 / f1|): 2.67 Condition (12) (|fc1 / fw|): 3.06 Condition (13) (|fg2e / fw|): 4.25 Condition (14) (|Rg2er / fw|:|Rdy16 / fw|):4.01 Condition (15) (|θt|): 5.79 Condition (16) (LB / LA): 0.35 Condition (17) (Rg2m / Rg2p:Rdy14 / Rdy13): 0.98 Condition (18) (θnm): 44.85 Condition (19) (θnp / θnm): 0.95 Condition (20) (SP3 / SD2:SP3 / H*2-37): 0.45 Condition (21) (SP4 / SD2:SP4 / H*2-37): 0.44 Condition (23) (fc1 / fc3): 1.05

[0116] This optical system 10 satisfies all of the above conditions (1) to (21) and (23). This optical system 10 also performs focusing mainly by the lens group arranged in the first refractive optical system RS1 on the enlargement side 3 of the intermediate image IM, and zooming by the lens group arranged in the second refractive optical system RS2 on the reduction side 2. Furthermore, by realizing a compact arrangement in which many lenses are closely packed in the second lens group G2, the entire system can be made compact, and a bright optical system 10 with a small F-number can be provided.

[0117] This optical system 10 is designed to have a relatively short back focus and a small image circle. Furthermore, many lenses with positive power are arranged in the third lens group G3 on the reduction side 2 of the intermediate image IM, and the intermediate image IM is reduced by bending light rays inward. Therefore, it is suitable for applications that do not require a large back focus. As shown in the aberration diagram, this optical system 10 also has good aberration correction during zooming and focusing, and as a projection optical system, it is possible to provide a projection optical system 10 that is capable of zooming and is compact yet capable of projecting an image with good aberration correction, and a projector 1 equipped with the projection optical system 10.

[0118] It should be noted that, although particular embodiments of the present invention have been described above, various other embodiments and modifications may be conceived by those skilled in the art without departing from the scope and spirit of the present invention, and such other embodiments and modifications are within the scope of the following claims, which define the present invention.

Claims

1. The optical system is composed of a first optical subsystem arranged on the enlargement side and a second optical subsystem arranged on the reduction side, with an intermediate image in between, The first optical subsystem includes a first lens group arranged on the magnification side at a first interval from a first aperture, the first interval being a distance at which other lenses can be arranged, but at which no other lenses are arranged, the first lens group having a first component of negative refractive power on the magnification side; an optical system including: a second lens having positive refractive power arranged on the reduction side at a second interval, at which no other lens is arranged, relative to the first aperture, the second lens group being adjacent to the reduction side and forming an intermediate image inclined toward the enlargement side.

2. In claim 1, An optical system, in which the first distance SP1, the second distance SP2, and an effective diameter SD1 of the first aperture satisfy the following condition: 0.5<SP1 / SD1<1.7 0.5<SP2 / SD1<1.7

3. In claim 1 or 2, An optical system, wherein an amount of field curvature IMFc of the intermediate image and a focal length f1 of the first optical subsystem satisfy the following condition: 0<|IMFc / f1|<2.5

4. In any one of claims 1 to 3, The optical system according to the present invention is one in which the second lens group includes a plurality of lenses, the maximum effective diameter Dg2max and the minimum effective diameter Dg2min of which satisfy the following condition: 1<Dg2max / Dg2min<1.7

5. In any one of claims 1 to 4, an optical system in which the second lens group includes a plurality of lenses of positive refractive power, and a length Lg2 from a surface of the second lens group facing the first aperture to a surface facing the intermediate image, and a thickness Lg2p occupied by the plurality of lenses of positive refractive power satisfy the following condition: 0.5<Lg2p / Lg2<1.0

6. In any one of claims 1 to 5, An optical system, wherein a focal length f1 of the first optical subsystem and a focal length fw of the optical system at a wide-angle end satisfy the following condition: 1.0<|f1 / fw|<2.0

7. In any one of claims 1 to 6, an optical system in which the second lens group includes a final lens having positive refractive power on the most reduced side and adjacent to the enlarged side of the intermediate image, and a focal length fg2e of the final lens and a focal length fw of the optical system at a wide-angle end satisfy the following condition: 2.5<|fg2e / fw|<10.0

8. In any one of claims 1 to 6, an optical system in which the second lens group includes a final lens having positive refractive power that is adjacent to the enlargement side of the intermediate image on the most reduced side, and a radius of curvature Rg2er of the enlargement side surface of the final lens and a focal length fw at the wide-angle end of the optical system satisfy the following condition: 2.0<|Rg2er / fw|<35.0

9. In any one of claims 1 to 8, The optical system includes a second component having a combination of positive-negative-positive refractive power, the second lens group being closest to an intermediate image.

10. In any one of claims 1 to 9, the second lens group includes a lens having positive refractive power and convex toward the reduction side, the lens being located closest to the intermediate image side.

11. In any one of claims 1 to 10, An optical system, wherein the first optical subsystem includes a focus group including a lens that moves during focusing, the focus group including a lens with negative refractive power included in the first component of the first lens group.

12. In claim 11, An optical system, wherein the focus group includes a first lens having negative refractive power that is disposed on the most magnifying side of the first lens group.

13. In claim 12, The optical system, wherein the focus group includes at least one lens included in the first optical subsystem in addition to the first lens.

14. In claim 12 or 13, an optical system, wherein the focus group includes, in addition to the first lens, at least one lens having a positive refractive power included in the second lens group.

15. In any one of claims 12 to 14, The optical system, wherein the focus group includes a first focus lens group including the first lens, and a second focus lens group that moves differently from the first focus lens group.

16. In any one of claims 1 to 15, The second optical subsystem includes a third lens group arranged on the magnification side at a third interval from the second aperture, the third interval being a distance at which another lens can be arranged and at which no other lens is arranged, the third lens group having a third component of negative refractive power on the magnification side; and a fourth lens group having positive refractive power arranged on a reduction side with respect to the second aperture at a fourth interval at which another lens can be arranged, but at which no other lens is arranged.

17. In claim 16, The optical system, in which the third distance SP3, the fourth distance SP4, and the effective diameter SD2 of the second diaphragm satisfy the following condition: 0.4<SP3 / SD2<1.5 0.4<SP4 / SD2<1.5

18. In claim 16 or 17, An optical system, wherein a focal length fc1 of the first component and a focal length fc3 of the third component satisfy the following condition: 0.1<fc1 / fc3<0.3

19. In claim 16 or 17, An optical system, wherein a focal length fc1 of the first component and a focal length fc3 of the third component satisfy the following condition: 0.8<fc1 / fc3<1.2

20. In any one of claims 16 to 19, An optical system, wherein a total length Lop of the optical system and a total length Lop1 of the first optical subsystem satisfy the following condition: 0.2<Lop1 / Lop<0.33

21. In any one of claims 16 to 20, an optical system, wherein the third component of the third lens group is disposed adjacent to the intermediate image and includes, in order from the magnification side, a lens having positive refractive power closest to the intermediate image and two lenses having negative refractive power.

22. In any one of claims 16 to 21, The optical system according to claim 1, wherein the third lens group includes, at the most magnifying side, a lens having positive refractive power that is convex toward the magnifying side and adjacent to the reduction side of the intermediate image.

23. In any one of claims 16 to 22, The second optical subsystem includes a zoom group that includes a lens that moves during zooming.

24. In claim 23, the zoom group includes a first zoom lens group including a lens of the third lens group, and a second zoom lens group including a lens of the fourth lens group.

25. An optical system according to any one of claims 1 to 24; and a light modulator disposed on the reduction side of the optical system.

26. An optical system according to any one of claims 1 to 24; and an image sensor disposed on the reduction side of the optical system.

Images