Optical system, lens apparatus, and image pickup apparatus

Abstract

To provide a compact, high-performance and low-cost optical system capable of performing stereoscopic photographing in which photographing by two photographing optical systems is performed by one imaging element.SOLUTION: The optical system includes, in order from the object side to the image side, a first lens unit L1 having a negative refractive power, a first reflective member PR1, a second lens unit L2 including an aperture diaphragm SP and having a positive refractive power, a second reflective member PR2, and a third lens unit L3 having a positive refractive power. A focal distance f of the optical system, a focal distance f1 of the first lens group, a focal distance f2 of the second lens group, a focal distance f3 of the third lens group, and a refraction index NPr of the first reflecting member satisfy predetermined conditional expressions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for digital video cameras, digital still cameras, broadcast cameras, cameras for silver halide film, surveillance cameras, and the like. [Background technology]

[0002] In order to provide a realistic video experience such as virtual reality, wide-angle lenses or fisheye lenses that can capture subjects with a wide angle of view are required. Fisheye lenses in particular have an angle of view of 180° or more, making it possible to provide a wide-field image with just one lens.

[0003] Furthermore, as a method for capturing realistic images, an imaging device has been proposed that horizontally arranges two optical systems to create parallax and captures images that can be viewed stereoscopically. Patent Document 1 discloses a method for providing an imaging optical system that can capture stereoscopic images with an interchangeable lens camera by integrating the image circles of two horizontally arranged fisheye lenses into a single imaging element. Here, the image circle refers to the area in which a captured image can be viewed, and the area outside the image circle is an area where the image cannot be viewed due to insufficient light or a sudden deterioration in optical performance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-008629 Summary of the Invention [Problem to be solved by the invention]

[0005] To capture a realistic three-dimensional image, it is recommended that the baseline length of the two horizontally arranged optical systems (the distance between the vertices of the lenses closest to the object in the two optical systems) be set to approximately the distance between human eyes (typically about 60 to 65 mm). Viewing captured images with a parallax equal to the distance between human eyes makes it possible to experience a realistic image. However, because the size of image sensors is generally smaller than the distance between human eyes, arranging regular fisheye lenses side by side poses a problem in that the image circle of the optical system falls outside the image sensor, resulting in vignetting of the angle of view. Therefore, Patent Document 1 proposes a photographic optical system that places two reflecting members within the fisheye lens and bends light rays to fit two image circles within the image sensor.

[0006] However, in a fisheye lens with two reflecting members, the overall length is long to ensure space for the reflecting members, and the lens closest to the object and the lens closest to the image are farther away from the aperture, so widening the angle of view tends to increase the lens outer diameter. Furthermore, when a reflecting member is placed in an optical system with a wide angle of view, such as a fisheye lens, the angular distribution of light rays incident on the reflecting surface widens, resulting in areas on the reflecting surface that are not fully reflected, making it necessary to apply a metal film such as silver or aluminum to the reflecting surface. This creates issues such as increased costs and concerns about corrosion of the metal film.

[0007] An object of the present invention is to realize a small, high-performance, low-cost optical system capable of stereoscopic photography, which performs photography using two optical systems with one image sensor. [Means for solving the problem]

[0008] An optical system according to one aspect of the present invention is an optical system comprising, arranged in order from the object side to the image side, a first lens group having negative refractive power, a first reflecting member, a second lens group having an aperture stop and having positive refractive power, the second reflecting member, and a third lens group having positive refractive power, wherein when the focal length of the optical system is f, the focal length of the first lens group is f1, the focal length of the second lens group is f2, the focal length of the third lens group is f3, the refractive index of the material of the first reflecting member to the d-line is NPr, and the refractive index of the positive lens having the greatest refractive power among the positive lenses constituting the first lens group to the d-line is N1p, then: -1.27<(f1 / f) / Npr<-0.70 0.60 <f2 / f3<1.60 1.78 <N1p<2.20 The present invention is characterized in that the following conditional expression is satisfied:

[0009] Other objects and features of the present invention will be described in the following embodiments. [Effects of the Invention]

[0010] According to the present invention, a small, high-performance, low-cost optical system capable of stereoscopic photography, which performs photography using two photographing optical systems with one image sensor, can be realized. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view of an optical system according to a first embodiment. [Figure 2] 4A to 4C are aberration diagrams of the optical system of Example 1 when focused at infinity. [Figure 3] FIG. 10 is a cross-sectional view of an optical system according to a second embodiment. [Figure 4] 10A and 10B are aberration diagrams of the optical system of Example 2 when focused at infinity. [Figure 5] FIG. 10 is a cross-sectional view of an optical system according to a third embodiment. [Figure 6] 10A and 10B are aberration diagrams of the optical system of Example 3 when focused at infinity. [Figure 7] FIG. 10 is a cross-sectional view of an optical system according to a fourth embodiment. [Figure 8] 10A and 10B are aberration diagrams of the optical system of Example 4 when focused at infinity. [Figure 9] FIG. 10 is a cross-sectional view of an optical system according to a fifth embodiment. [Figure 10] 10A and 10B are aberration diagrams of the optical system of Example 5 when focused at infinity. [Figure 11] 1 is a cross-sectional view of a main part of a lens device in which two optical systems of Example 1 are arranged, showing a state in which an optical path is bent by a reflecting member. [Figure 12] FIG. 1 is a schematic diagram of an imaging device. DETAILED DESCRIPTION OF THE INVENTION

[0012] The optical system according to each embodiment will be described below with reference to the accompanying drawings. In each embodiment, two optical systems are arranged in parallel with the image sensor to obtain an image that can be viewed stereoscopically.

[0013] Figures 1, 3, 5, 7, and 9 are cross-sectional views of the optical systems of Examples 1, 2, 3, 4, and 5, respectively. As will be described later, the optical system of each Example has two reflecting members, reflecting prisms PR1 (first reflecting member) and PR2 (second reflecting member), and actually reflects the optical path twice (the optical path is bent twice). Figures 1, 3, 5, 7, and 9 show cross-sectional views of the optical system when the optical path is not reflected.

[0014] 2, 4, 6, 8, and 10 are aberration diagrams of the optical systems of Examples 1, 2, 3, 4, and 5 when focused at infinity, respectively.

[0015] FIG. 11 shows a lens device 100 in which two optical systems of Example 1 (a first optical system 101 and a second optical system 102) are arranged in parallel, and illustrates a state in which incident light rays are bent by a reflecting prism and the image circles of the two optical systems are formed within one image sensor. The two optical systems are held by a housing (not shown). Note that FIG. 11 shows an example in which two optical systems of Example 1 are arranged as a representative example, but two optical systems of other Examples may also be arranged.

[0016] The optical system of each embodiment is an optical system used in an imaging device capable of capturing a wide-angle image of a subject as a stereoscopic image, such as in panoramic photography.

[0017] In each lens cross-sectional view, the left side is the object side (front) and the right side is the image side (rear). The optical system in each embodiment is configured with multiple lens groups. A lens group may be composed of a single lens or multiple lenses. The lens group may also include an aperture stop.

[0018] In each lens cross-sectional view, Li represents the ith lens group (i is a natural number) counting from the object side. SP is an aperture stop. IP is an image plane. When the optical system of each embodiment is used as the photographic optical system of a digital still camera or digital video camera, the imaging surface of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor is disposed on the image plane IP. When the optical system of each embodiment is used as the photographic optical system of a silver halide film camera, a photosensitive surface equivalent to the film surface is disposed on the image plane IP. Although not shown, the optical system of each embodiment may have optical blocks equivalent to an optical filter, face plate, low-pass filter, infrared cut filter, etc. disposed on the object side of the image plane IP. Both PR1 and PR2 are prisms.

[0019] In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm). In the astigmatism diagram, ΔS shows the amount of astigmatism on the sagittal image plane, and ΔM shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the half angle of view (°).

[0020] To experience a realistic 3D image when viewing captured images on a head-mounted display, etc., it is best to set the distance between the optical axes of the two optical systems (baseline length) at the time of capture to be approximately the same as the distance between human eyes. Generally, the distance between human eyes is approximately 60-65 mm. The greater the difference from the distance between the two optical systems, the greater the deviation from the stereoscopic sensation based on human experience, causing discomfort. If the baseline length is too short, there will be no parallax between the left and right optical systems, and the captured image will not have a sense of 3D. Conversely, if the baseline length is too long, there will be too much parallax, which will emphasize the 3D sensation when viewing the captured image, potentially causing fatigue for the viewer.

[0021] The optical system in each example is based on an image sensor typically used in interchangeable lens cameras, with a short side length of 24 mm and a long side length of 36 mm. When the baseline length is set to 60 mm, the long side length of the image sensor is 36 mm. Therefore, even if fisheye lenses that do not use typical reflecting components are arranged side by side, the image circles of each optical system will not fit within the image sensor, resulting in a vignetting angle. Therefore, as shown in FIG. 11, the optical system in each example has two reflecting prisms arranged within the optical system, allowing the image circles of the two optical systems to fit onto a single image sensor.

[0022] Since the long side of the image sensor is 36 mm, the length of the long side of the image sensor that can be used by one optical system is 18 mm. The image circle of the optical system in each example is 17.5 mm, and a 1 mm gap is set between the image circles of the two optical systems. In this case, the gap (Dout) between the vertices of the lenses located closest to the image side in the two optical systems is 18.5 mm. Since the base length is set to 60 mm in each of the optical systems in Examples 1 to 4, the gap (Din) between the vertices of the lenses located closest to the object side in the two optical systems is 60 mm. Since the base length is set to 65 mm in the optical system in Example 5, the gap (Din) between the vertices of the lenses located closest to the object side in the two optical systems is 65 mm. Furthermore, the image circle of each optical system is inscribed in the short side of the image sensor. In addition, in Examples 1 to 4, when the base length is set to 60 mm and the distance between the vertices of the lenses located closest to the image in the two optical systems is set to 18.5 mm, the length on the optical axis between the two reflecting surfaces of each optical system is 20.75 mm. In Example 5, when the base length is set to 65 mm and the distance between the vertices of the lenses located closest to the image in the two optical systems is set to 18.5 mm, the length on the optical axis between the two reflecting surfaces of each optical system is 23.25 mm. Note that the optical systems in each Example are assumed to use an image sensor with a short side length of 24 mm and a long side length of 36 mm, which is generally used in interchangeable lens cameras, but this is not limiting and the system can be applied to cameras with image sensors of various sizes. The distance between the two image circles can also be set arbitrarily.

[0023] Furthermore, the optical systems in each embodiment employ conformal projection. Conformal projection is defined as y = fω, where y is the half image height, ω is the half angle of view, and f is the focal length. However, there are various projection methods, such as conformal solid angle projection and stereographic projection, and the projection method to be used is optional.

[0024] Next, the characteristic configuration of the optical system of each embodiment will be described.

[0025] The optical system of each embodiment is composed of, arranged in order from the object side to the image side, a first lens unit L1 with negative refractive power, a first reflecting prism PR1, a second lens unit L2 with positive refractive power and equipped with an aperture stop SP, a second reflecting prism PR2, and a third lens unit L3 with positive refractive power. Overall, a so-called retrofocus type refractive power arrangement is used, consisting of a front group with negative refractive power and a rear group with positive refractive power, thereby achieving a compact size and a wide angle of view.

[0026] In the optical systems of each embodiment, an aperture stop SP is disposed between the reflecting surfaces of the two prisms. As shown in FIG. 11 , in order to form the image circles of the two optical systems (first optical system 101 and second optical system 102) on a single image sensor, the lenses subsequent to the second reflecting prism PR2 must be disposed closely together. Therefore, if the aperture stop SP is disposed on the object side of the first reflecting prism PR1, the lens diameter of the image-side lens increases, causing problems such as interference with adjacent lenses. If the aperture stop SP is disposed on the image side of the second reflecting prism PR2, the lens diameter on the object side increases, causing problems such as increased weight and interference with adjacent lenses.

[0027] As mentioned above, when a prism is placed in a wide-angle optical system to bend light rays, the angle distribution of light incident on the reflecting surface becomes wide, resulting in angles of view where total reflection does not occur. When there are angles of view where total reflection does not occur, metal deposition such as silver or aluminum is required on the reflecting surface, which increases costs.

[0028] The angle of light rays incident on the reflecting surface of the first reflecting prism PR1 is determined by the refractive power of the first lens group L1. The reflecting surface of the first reflecting prism PR1 is tilted at 45° with respect to the optical axis. To reduce the distribution of incident angles on the reflecting surface and achieve total reflection of light rays at all image heights, it is advisable to strengthen the refractive power of the first lens group L1 so that off-axial light rays passing through the first lens group L1 are parallel to the optical axis. However, if the refractive power of the first lens group L1 is too strong, off-axial aberrations such as field curvature and distortion become significantly worse. Furthermore, the strong refractive power of the first lens group L1 significantly diverges on-axis light rays, increasing the effective diameter of the second reflecting prism PR2 and making it larger. The larger prism increases the distance between the third lens group L3 and the aperture stop SP, which increases the size of the lenses comprising the third lens group L3 and causes interference with adjacent lenses. Therefore, it is necessary to appropriately set the refractive power of the first lens group L1. The angle of total reflection of a prism reflecting surface is determined by the refractive power of the prism. The angle of total reflection θ when light propagates from medium A (refractive index Na) to medium B (refractive index Nb) is defined as sinθ = Nb / Na. In the case of a prism, the higher the refractive index of the prism, the smaller the angle of total reflection, making total reflection easier. Therefore, it is advisable to set the refractive power of the first lens unit L1 according to the refractive index of the prism, and to set an optimal refractive power within a range in which light rays at all image heights are totally reflected. Therefore, the optical systems of each embodiment satisfy the following conditional expression (1), where f1 is the focal length of the first lens unit L1, f is the focal length of the entire optical system, and Npr is the refractive index of the first reflecting prism PR1.

[0029] -1.27<(f1 / f) / Npr<-0.70 (1) Conditional formula (1) is a conditional formula relating the refractive power of the first lens group L1 to the refractive index of the first reflecting prism PR1. If the lower limit of conditional formula (1) is not met, the refractive power of the first lens group L1 becomes too strong, which, as mentioned above, causes the lenses constituting the third lens group L1 to become large and interfere with adjacent lenses, resulting in problems. Furthermore, off-axis aberrations occurring in the first lens group L1 worsen, resulting in problems. If the upper limit of conditional formula (1) is met, the refractive power of the first lens group L1 becomes too weak, which causes problems such as light rays not being totally reflected at all image heights and the first lens group L1 becoming large.

[0030] Furthermore, it is preferable that the numerical range of conditional expression (1) be within the range of the following conditional expression (1a).

[0031] -1.26<(f1 / f) / Npr<-0.75 (1a) It is more preferable that the numerical range of conditional expression (1) satisfies the range of the following conditional expression (1b).

[0032] -1.25<(f1 / f) / Npr<-0.80 (1b) In addition, the optical systems of each embodiment include a second lens group L2 with positive refractive power located between the first reflecting prism PR1 and the second reflecting prism PR2. The second lens group L2 converges the on-axis light beam diverged by the first lens group L1, which has a strong refractive power, and directs it toward the second reflecting prism PR2, thereby reducing the size of the second reflecting prism PR2. Furthermore, the second lens group L2 converges off-axis light rays that pass through the aperture stop SP toward the optical axis, thereby reducing the size of the third lens group L3. However, the distance between the first reflecting prism PR1 and the second reflecting prism PR2, where the second lens group L2 is located, is determined by the base length required for stereoscopic imaging, and therefore does not have a large space. Therefore, it is not possible to place many lenses in the second lens group L2. Setting a strong refractive power for the second lens group L2 would worsen spherical aberration and coma, degrading optical performance. Therefore, it is necessary to optimally set the refractive power distribution between the second lens group L2 and the third lens group L3 with positive refractive power. The third lens group L3 is located away from the aperture stop SP, and the lens outer diameter determined by off-axial rays tends to be large. However, the third lens group L3 with positive refractive power has the effect of converging off-axial rays by itself, thereby reducing the increase in lens outer diameter. Therefore, it is necessary to appropriately set the refractive power distribution of the second lens group L2 and the third lens group L3 so that the lenses constituting the third lens group L3 do not become large. Therefore, the optical system of each embodiment satisfies the following conditional expression (2), where the focal length of the second lens group L2 is f2 and the focal length of the third lens group L3 is f3.

[0033] 0.60 <f2 / f3<1.60 ···(2) Conditional expression (2) is a conditional expression for appropriately setting the refractive power distribution between the second lens unit L2 and the third lens unit L3. If the lower limit of conditional expression (2) is not met, the refractive power of the second lens unit L2 becomes too strong, which, as mentioned above, causes problems such as worsening spherical aberration and coma. If the upper limit of conditional expression (3) is met, as mentioned above, the second reflecting prism PR2 becomes large, and the subsequent third lens unit L3 also becomes large, which causes problems such as interference with adjacent lenses.

[0034] Furthermore, it is preferable that the numerical range of conditional expression (2) is set to the range of the following conditional expression (2a).

[0035] 0.65 <f2 / f3<1.50 ···(2a) It is more preferable that the numerical range of conditional expression (2) satisfies the range of the following conditional expression (2b).

[0036] 0.72 <f2 / f3<1.40 ···(2b) As described above, according to each embodiment, a small, high-performance, low-cost optical system capable of stereoscopic imaging, which performs imaging by two optical systems with one imaging element, can be realized.

[0037] Next, conditions and configurations that the optical system of each embodiment should preferably satisfy will be described. The optical system of each embodiment should preferably satisfy one or more of the following conditional expressions and configurations.

[0038] In the optical system of each embodiment, it is preferable that the following conditional expression (3) be satisfied, where f2 is the focal length of the second lens unit L2.

[0039] 4.80 <f2 / f<10.50 ···(3) Conditional expression (3) is a conditional expression relating to optical performance and miniaturization of the lenses in the third lens unit L3. If the lower limit of conditional expression (3) is not met, the refractive power of the second lens unit L2 becomes too strong, which, as mentioned above, causes problems such as worsening of on-axis aberrations like spherical aberration and coma. If the upper limit of conditional expression (3) is met, the third lens unit L3 becomes too large, which, as mentioned above, causes problems such as interference with adjacent lenses.

[0040] It is more preferable that the numerical range of conditional expression (3) satisfies the range of the following conditional expression (3a).

[0041] 5.00 <f2 / f<9.50 ···(3a) It is more preferable that the numerical range of conditional expression (3) satisfies the range of the following conditional expression (3b).

[0042] 5.27 <f2 / f<8.50 ···(3b) In addition, in the optical systems of each embodiment, it is preferable that the first lens group L1 be composed of two or more negative lenses and one or more positive lenses. As described above, the optical systems of each embodiment include two prisms, with the first lens group L1, which has negative refractive power, and the third lens group L3, which has positive refractive power, being positioned away from the aperture stop SP, resulting in an asymmetric refractive power arrangement with respect to the aperture stop SP. As a result, it is difficult to cancel out off-axis aberrations, such as lateral chromatic aberration and astigmatism, that occur in the first lens group L1 with off-axis aberrations that occur in the third lens group L3, and therefore aberrations must be corrected in each lens group. In particular, the first lens group L1 has a strong negative refractive power in order to totally reflect light rays at all image heights with the first reflecting prism PR1. To reduce off-axis aberrations, it is preferable to use at least two or more negative lenses to reduce the off-axis aberrations that occur in the negative lenses. Furthermore, it is preferable to arrange at least one positive lens in the first lens unit L1 so that the off-axis aberrations generated by the negative lens are corrected by the positive lens.

[0043] Furthermore, it is preferable that the optical system of each embodiment satisfies the following conditional expression (4), where N1Aave is the average value of the refractive index for the d-line of the negative lenses that make up the first lens unit L1.

[0044] 1.78 <N1Aave<2.20 ···(4) Conditional formula (4) is a conditional formula related to optical performance. As mentioned above, the first lens group L1 has a strong negative refractive power in order to totally reflect light rays at all image heights at the first reflecting prism PR1. As a result, off-axis aberrations such as astigmatism and field curvature are likely to occur. To achieve high image quality, it is advisable to use a glass material with a high refractive index for the negative lens that constitutes the first lens group L1. If the lower limit of conditional formula (4) is not met, the refractive index of the negative lens in the first lens group L1 will be too low, and off-axis aberrations will worsen. If the upper limit of conditional formula (4) is exceeded, the lens will be less easy to process, resulting in problems such as increased costs.

[0045] It is more preferable that the numerical range of conditional expression (4) satisfies the range of the following conditional expression (4a).

[0046] 1.80 <N1Aave<2.10 ···(4a) It is more preferable that the numerical range of conditional expression (4) satisfies the range of the following conditional expression (4b).

[0047] 1.82 <N1Aave<2.05 ···(4b) In addition, it is preferable that the optical system of each embodiment satisfies the following conditional expression (5), where N1p is the refractive index for the d-line of the positive lens with the greatest refractive power among the positive lenses constituting the first lens unit L1.

[0048] 1.78 <N1p<2.20 ···(5) Conditional formula (5) is a conditional formula related to optical performance. As mentioned above, positive lenses are provided to correct off-axis aberrations that occur in the first lens unit L1, which has a strong refractive power. However, providing a large number of positive lenses would result in the first lens unit becoming larger, which would be a problem. Therefore, it is necessary to correct aberrations with a small number of positive lenses, which requires the positive lenses to be made of a material with a high refractive index. If the lower limit of conditional formula (5) is exceeded, the refractive index of the positive lenses becomes too low, making it difficult to correct off-axis aberrations that occur in negative lenses with a small number of positive lenses. If the upper limit of conditional formula (5) is exceeded, the lens fabrication becomes difficult, which would result in problems such as increased costs.

[0049] It is more preferable that the numerical range of conditional expression (5) satisfies the range of the following conditional expression (5a).

[0050] 1.79 <N1p<2.10 ···(5a) It is more preferable that the numerical range of conditional expression (5) satisfies the range of the following conditional expression (5b).

[0051] 1.80 <N1p<2.05 ···(5b) Furthermore, it is preferable that the optical system of each embodiment satisfies the following conditional expression (6), where LP is the distance between the reflecting surfaces of the first reflecting prism PR1 and the second reflecting prism PR2 on the optical axis.

[0052] 1.00 <f2 / LP<2.40 ···(6) Conditional formula (6) is a conditional formula related to ensuring the base length and interference between adjacent lenses. As mentioned above, the second lens group L2 minimizes the size of the second reflecting prism PR2, which in turn minimizes the size of the third lens group, preventing interference with adjacent lens groups. The base length is determined by the distance between the axial reflecting surfaces of the first reflecting prism PR1 and the second reflecting prism PR2. To achieve natural stereoscopic photography, the base length must be set to approximately the distance between the human eyes, which imposes length restrictions. Because an aperture stop SP is also located between the first reflecting prism PR1 and the second reflecting prism PR2, it is not possible to arrange multiple lenses. For this reason, it is important to appropriately configure the refractive power of the second lens group L2. If the lower limit of conditional formula (6) is exceeded and the refractive power of the second lens group L2 becomes too strong, it is not possible to arrange multiple lenses to correct spherical aberration and coma, resulting in a problem of degraded optical performance. If the upper limit of conditional expression (6) is exceeded, the third lens unit L3 becomes large, causing interference with adjacent lenses, which becomes a problem.

[0053] It is more preferable that the numerical range of conditional expression (6) satisfies the range of the following conditional expression (6a).

[0054] 1.10 <f2 / LP<2.20 ···(6a) It is more preferable that the numerical range of conditional expression (6) satisfies the range of the following conditional expression (6b).

[0055] 1.20 <f2 / LP<2.00 ···(6b) It is also preferable that the optical system of each embodiment satisfies the following conditional expression (7).

[0056] 1.00 <f3 / LP<2.20 ···(7) As mentioned above, the second lens group L2 has the effect of making the third lens group L3 smaller, but because the distance between the first reflecting prism PR1 and the second reflecting prism PR2 is determined by the base length, interference with adjacent lenses cannot be avoided by the second lens group L2 alone. Therefore, the refractive power of the third lens group L3 must be appropriately determined. If the lower limit of conditional expression (7) is not met and the refractive power of the third lens group becomes too strong, significant coma and astigmatism will occur, causing problems. If the upper limit of conditional expression (7) is exceeded, interference with adjacent lenses will occur, causing problems.

[0057] It is more preferable that the numerical range of conditional expression (7) satisfies the range of the following conditional expression (7a).

[0058] 1.10 <f3 / LP<2.00 ···(7a) It is more preferable that the numerical range of conditional expression (7) satisfies the range of the following conditional expression (7b).

[0059] 1.20 <f3 / LP<1.75 ···(7b) It is also preferable that the optical system of each embodiment satisfies the following conditional expression.

[0060] 1.78 <Npr<2.20 ···(8) Conditional expression (8) is a conditional expression regarding the refractive index of the first reflecting prism PR1 to ensure that light rays at all angles of view are totally reflected. If the lower limit of conditional expression (8) is not met, the total reflection angle of the reflecting surface becomes small, which, as mentioned above, requires the refractive power of the first lens unit L1 to be increased, resulting in problems such as worsening off-axis aberrations like astigmatism and field curvature. If the upper limit of conditional expression (8) is exceeded, the thickness of the glass of the prism increases, significantly reducing transmittance and causing problems. Furthermore, processability deteriorates, resulting in increased costs.

[0061] It is more preferable that the numerical range of conditional expression (8) satisfies the range of the following conditional expression (8a).

[0062] 1.79 <Npr<2.10 ···(8a) It is more preferable that the numerical range of conditional expression (8) satisfies the range of the following conditional expression (8b).

[0063] 1.79 <Npr<2.05 ···(8b) Furthermore, it is preferable that the optical system of each embodiment satisfies the following conditional expression (9) when two optical systems are arranged in parallel as shown in Fig. 11. Here, the distance between the vertices of the lenses located closest to the object in the two optical systems is defined as Din, and the distance between the vertices of the lenses located closest to the image in the two optical systems is defined as Dout.

[0064] 0.05 <Dout / Din<0.50 ···(9) Conditional formula (9) is a conditional formula related to the sense of three-dimensionality and discomfort when viewing a captured image. If the lower limit of conditional formula (9) is not met, the baseline length will be much wider than the distance between the human eyes, resulting in excessive parallax and increasing the likelihood that the viewer will feel fatigued. If the upper limit of conditional formula (9) is exceeded, the captured image will not have parallax, and so a sense of three-dimensionality will not be achieved.

[0065] It is more preferable that the numerical range of conditional expression (9) satisfies the range of the following conditional expression (9a).

[0066] 0.10 <Dout / Din<0.45 ···(9a) It is more preferable that the numerical range of conditional expression (9) satisfies the range of the following conditional expression (9b).

[0067] 0.15 <Dout / Din<0.40 ···(9b) Furthermore, it is preferable that the optical system of each embodiment satisfies the following conditional expression (10), where ω is the half angle of view (°) of the optical system of each embodiment.

[0068] 85.0°<ω<120.0° (10) If the lower limit of conditional expression (10) is exceeded, the angle of view is insufficient when viewing the captured image, making it impossible to obtain a sufficient sense of realism.If the upper limit of conditional expression (10) is exceeded, the number of pixels per incident angle on the image sensor decreases, causing a problem of insufficient resolution when viewing the image.

[0069] It is more preferable that the numerical range of conditional expression (10) satisfies the range of the following conditional expression (10a).

[0070] 87.0°<ω<115.0° (10a) It is more preferable that the numerical range of conditional expression (10) satisfies the range of the following conditional expression (10b).

[0071] 89.0°<ω<110.0° (10b) Next, the configuration of each lens group in the optical system of each embodiment will be described.

[0072] In Examples 1, 2, 4, and 5, the first lens unit L1 is composed of, arranged in order from the object side to the image side, a negative meniscus lens with a convex surface on the object side, a negative meniscus lens with a convex surface on the object side, a biconcave lens, and a positive lens. In Example 3, the first lens unit L1 is composed of, arranged in order from the object side to the image side, a negative meniscus lens with a convex surface on the object side, a negative meniscus lens with a convex surface on the object side, a biconcave lens, a positive lens with a convex surface on the image side, and a negative meniscus lens with a convex surface on the image side. An aspheric surface is arranged on the surface of the first lens unit L1 closest to the image side to correct off-axis aberrations such as astigmatism.

[0073] In Examples 1 to 5, the second lens unit L2 is composed of, arranged in order from the object side to the image side, an aperture stop SP, a negative meniscus lens with a convex surface on the object side, and a cemented lens made of a biconvex lens.

[0074] In Examples 1, 3, 4, and 5, the third lens unit L3 is composed of, arranged in order from the object side to the image side, a biconvex lens, a cemented lens of a biconcave lens and a biconvex lens, and a cemented lens of a negative meniscus lens with a convex surface on the object side and a biconvex lens. In Example 2, the third lens unit L3 is composed of, arranged in order from the object side to the image side, a biconvex lens, a cemented lens of a negative meniscus lens with a convex surface on the image side and a positive meniscus lens with a convex surface on the image side, and a cemented lens of a negative meniscus lens with a convex surface on the object side and a biconvex lens.

[0075] In the optical system of each embodiment, a first reflecting prism PR1 is disposed between the first lens group L1 and the second lens group L2, and a second reflecting prism PR2 is disposed between the second lens group L2 and the third lens group L3.

[0076] Numerical Examples 1 to 5 corresponding to Examples 1 to 5, respectively, are shown below.

[0077] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial spacing (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. Also, nd represents the refractive index of each optical element with respect to the d-line, and vd represents the Abbe number of the optical element. Note that the Abbe number vd of a certain material is given by the following when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines are Nd, NF, and NC, respectively: νd=(Nd-1) / (NF-NC) It is expressed as:

[0078] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values ​​when the optical system of each example is focused on an object at infinity. "Back focus" is the distance on the optical axis from the final lens surface (the lens surface closest to the image) to the paraxial image plane, expressed as an air-equivalent length. "Total lens length" is the distance on the optical axis from the forefront lens surface (the lens surface closest to the object) to the final lens surface plus the back focus. "Lens group" is not limited to cases where it is composed of multiple lenses, but also includes cases where it is composed of a single lens.

[0079] The reflecting member in Numerical Examples 1 to 5 is described as a single block. In reality, the reflecting member of each lens is arranged so as to bend light rays at a 45° angle with the center of the block as the reference. Furthermore, Numerical Examples 1 to 5 employ a system in which the entire optical system is extended when focusing from an object at infinity to an object at a close distance. However, in order to reduce the weight of the driving unit, focusing can also be performed by driving some of the lenses in the optical system.

[0080] If the optical surface is aspherical, an asterisk (*) is added to the right of the surface number. The aspherical shape is expressed as follows: X is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, and A10 are the aspherical coefficients of each order. x=(h2 / R) / [1+{1-(1+k)(h / R)2}1 / 2 +A4×h4+A6×h6+A8×h8+A10×h10] In addition, "e±XX" in each aspherical coefficient means "×10±XX."

[0081] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 28.343 1.75 2.00100 29.1 38.52 2 9.613 8.11 19.23 3 18.666 0.95 1.95375 32.3 17.58 4 10.629 7.18 14.89 5 -12.328 0.95 1.88300 40.8 11.95 6 41.971 1.81 12.16 7 -92.352 3.50 2.00069 25.5 12.63 8 -15.446 1.00 13.23 9 ∞ 13.00 1.88300 40.8 12.18 10 ∞ 3.00 9.29 11 (Aperture) ∞ 0.50 9.16 12 23.042 0.70 1.90043 37.4 9.39 13 12.054 3.80 1.54072 47.2 9.31 14 -17.283 0.25 9.54 15 ∞ 12.00 1.88300 40.8 9.40 16 ∞ 3.10 8.44 17 10.000 3.59 1.43875 94.7 9.39 18 -12.548 0.20 9.45 19 -13.486 0.85 1.83481 42.7 9.35 20 10.509 4.12 1.49700 81.5 9.84 21 -18.811 0.30 10.85 22 26.600 0.75 1.90043 37.4 11.58 23 10.300 5.33 1.49700 81.5 11.58 24 -24.585 13.51 12.67 Image plane ∞ Various data Focal length 4.77 F-number 2.80 Half angle of view (°) 105.00 Image height 8.75 Lens total length 90.26 BF 13.51 Entrance pupil position 9.71 Exit pupil position -48.26 Front principal point position 14.11 Back principal point position 8.74 Zoom lens group data Group Starting surface Ending surface Focal length Lens length Front principal point position Rear principal point position L1 1 8 -7.50 24.25 3.63 -21.16 L2 11 14 25.15 5.00 2.48 -0.96 L3 17 24 34.56 15.15 5.52 -6.30 Single lens data Lens starting surface focal length 1 1 -15.25 2 3 -27.47 3 5 -10.70 4 7 18.12 5 9 0.00 6 12 -28.94 7 13 13.76 8 15 0.00 9 17 13.33 10 19 -6.96 11 20 14.23 12 22 -19.08 13 23 15.39 [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 30.662 1.75 2.00100 29.1 37.36 2 10.632 6.34 20.97 3 15.903 0.95 1.95375 32.3 19.50 4 10.310 7.56 16.54 5 -14.405 0.95 1.88300 40.8 15.33 6 63.419 1.71 15.98 7 -684.604 3.97 2.00069 25.5 16.66 8 -17.774 6.90 17.20 9 ∞ 13.00 1.80400 46.6 12.20 10 ∞ 3.00 8.35 11 (Aperture) ∞ 0.50 8.81 12 54.465 0.70 1.90043 37.4 8.93 13 16.308 3.80 1.54072 47.2 8.94 14 -18.168 0.25 9.31 15 ∞ 12.00 1.80400 46.6 9.25 16 ∞ 1.50 8.84 17 12.316 3.70 1.43875 94.7 10.49 18 -14.278 0.20 10.63 19 -14.474 0.85 1.83481 42.7 10.58 20 -52.284 2.50 1.49700 81.5 10.95 21 -24.541 2.23 11.47 22 30.550 0.75 1.90043 37.4 11.91 23 8.684 6.50 1.49700 81.5 11.62 24 -29.335 13.80 12.90 Image plane ∞ Various data Focal length 5.23 F-number 2.80 Half angle of view (°) 95.00 Image height 8.75 Lens length 95.41 BF 13.80 Entrance pupil position 10.51 Exit pupil position -42.54 Front principal point position 15.25 Back principal point position 8.57 Zoom lens group data Group Starting surface Ending surface Focal length Lens length Front principal point position Rear principal point position L1 1 8 -11.68 23.23 1.33 -25.58 L2 11 14 40.67 5.00 3.63 0.29 L3 17 24 29.39 16.73 3.36 -9.98 Single lens data Lens starting surface focal length 1 1 -17.00 2 3 -33.52 3 5 -13.22 4 7 18.18 5 9 0.00 6 12 -26.08 7 13 16.53 8 15 0.00 9 17 15.74 10 19 -24.22 11 20 90.36 12 22 -13.70 13 23 14.29 [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 30.693 1.75 2.00100 29.1 38.50 2 10.349 6.11 20.53 3 13.633 0.95 1.95375 32.3 18.75 4 9.700 7.11 15.93 5 -14.738 0.95 1.88300 40.8 14.32 6 46.991 2.60 14.35 7 -30.443 3.65 2.00069 25.5 14.69 8 -12.138 0.87 15.40 9 -10.704 1.50 1.58313 59.4 14.32 10* -13.292 2.00 14.65 11 ∞ 13.00 2.00100 29.1 12.20 12 ∞ 3.00 8.51 13 (Aperture) ∞ 0.50 8.33 14 25.744 0.70 1.90043 37.4 8.48 15 10.952 3.80 1.54072 47.2 8.39 16 -17.073 0.25 8.65 17 ∞ 12.00 2.00100 29.1 8.55 18 ∞ 2.40 8.00 19 15.444 3.33 1.43875 94.7 9.99 20 -13.632 0.20 10.26 21 -17.826 0.85 1.83481 42.7 10.22 22 13.680 4.08 1.49700 81.5 10.82 23 -20.838 0.30 11.86 24 21.402 0.75 1.90043 37.4 12.83 25 10.309 6.04 1.49700 81.5 12.68 26 -26.154 13.51 13.72 Image plane ∞ Aspheric data Side 10 K = 0.00000e+000 A 4= 1.30637e-005 A 6=-1.61010e-007 A 8= 1.57831e-009 A10=-2.84708e-011 Various data Focal length 4.75 F-number 2.80 Half angle of view (°) 105.00 Image height 8.75 Lens length 92.20 BF 13.51 Entrance pupil position 9.99 Exit pupil position -61.11 Front principal point position 14.44 Back principal point position 8.76 Zoom lens group data Group Starting surface Ending surface Focal length Lens length Front principal point position Rear principal point position L1 1 10 -10.67 25.49 1.52 -29.45 L2 13 16 29.75 5.00 2.84 -0.57 L3 19 26 29.06 15.55 6.81 -4.80 Single lens data Lens starting surface focal length 1 1 -16.30 2 3 -39.96 3 5 -12.61 4 7 18.34 5 9 -119.83 6 11 0.00 7 14 -21.66 8 15 12.96 9 17 0.00 10 19 17.10 11 21 -9.16 12 22 17.29 13 24 -22.82 14 25 15.74 [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 26.962 1.75 2.00100 29.1 34.49 2 10.032 5.92 19.78 3 14.571 0.95 1.95375 32.3 18.31 4 9.653 8.18 15.52 5 -14.766 0.95 1.88300 40.8 12.50 6 28.464 1.69 12.50 7 134.987 4.09 2.00069 25.5 12.98 8 -18.112 1.00 13.40 9 ∞ 13.00 1.80400 46.6 12.20 10 ∞ 3.00 8.52 11 (Aperture) ∞ 0.50 8.85 12 36.531 0.70 1.90043 37.4 9.01 13 13.128 3.80 1.54072 47.2 8.99 14 -15.722 0.25 9.34 15 ∞ 12.00 1.80400 46.6 9.25 16 ∞ 1.50 8.59 17 12.789 3.23 1.43875 94.7 9.31 18 -13.722 0.20 9.54 19 -14.620 0.85 1.83481 42.7 9.52 20 46.520 3.11 1.49700 81.5 10.01 21 -19.985 0.30 10.78 22 30.290 0.75 1.90043 37.4 11.20 23 9.710 6.50 1.49700 81.5 11.13 24 -28.547 15.35 12.56 Image plane ∞ Various data Focal length 5.52 F-number 2.80 Half angle of view (°) 90.00 Image height 8.75 Lens length 89.57 BF 15.35 Entrance pupil position 10.11 Exit pupil position -41.89 Front principal point position 15.09 Back principal point position 9.83 Zoom lens group data Group Starting surface Ending surface Focal length Lens length Front principal point position Rear principal point position L1 1 8 -10.49 23.53 2.00 -24.50 L2 11 14 31.46 5.00 3.28 -0.09 L3 17 24 31.64 14.94 4.50 -6.76 Single lens data Lens starting surface focal length 1 1 -16.83 2 3 -33.11 3 5 -10.90 4 7 16.17 5 9 0.00 6 12 -23.09 7 13 13.87 8 15 0.00 9 17 15.67 10 19 -13.24 11 20 28.57 12 22 -16.15 13 23 15.45 [Numerical Example 5] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 26.206 1.75 2.00100 29.1 31.96 2 9.259 5.00 18.19 3 12.311 0.95 2.00100 29.1 16.82 4 9.324 6.64 14.68 5 -14.733 0.95 1.95375 32.3 12.71 6 33.722 1.95 12.74 7 137.773 3.88 1.80810 22.8 13.33 8 -15.142 1.00 13.69 9 ∞ 13.00 1.80400 46.6 12.21 10 ∞ 4.75 8.27 11 (Aperture) ∞ 0.50 8.85 12 41.415 0.70 1.90043 37.4 9.00 13 13.820 3.80 1.54072 47.2 9.00 14 -16.280 1.00 9.38 15 ∞ 12.00 1.80400 46.6 9.26 16 ∞ 1.50 10.08 17 14.453 3.90 1.43875 94.7 11.73 18 -15.731 0.20 11.88 19 -16.263 0.85 1.83481 42.7 11.83 20 49.982 3.70 1.49700 81.5 12.38 21 -18.284 1.36 13.13 22 23.655 0.75 1.90043 37.4 13.68 23 9.552 6.35 1.49700 81.5 13.19 24 -42.522 14.83 14.01 Image plane ∞ Various data Focal length 5.52 F-number 2.80 Half angle of view (°) 90.00 Image height 8.75 Lens length 91.31 BF 14.83 Entrance pupil position 9.55 Exit pupil position -52.47 Front principal point position 14.61 Back principal point position 9.31 Zoom lens group data Group Starting surface Ending surface Focal length Lens length Front principal point position Rear principal point position L1 1 8 -10.29 21.12 1.58 -22.21 L2 11 14 34.24 5.00 3.42 0.07 L3 17 24 29.81 17.11 4.94 -8.16 Single lens data Lens starting surface focal length 1 1 -15.08 2 3 -45.65 3 5 -10.65 4 7 17.08 5 9 0.00 6 12 -23.32 7 13 14.46 8 15 0.00 9 17 17.87 10 19 -14.61 11 20 27.43 12 22 -18.25 13 23 16.36 The various values ​​in each numerical example are summarized in Table 1 below.

[0082] [Table 1]

[0083] [Imaging device] Next, an embodiment of the imaging device of the present invention will be described. FIG. 12 is a schematic diagram of an imaging device (digital still camera) 200 of this embodiment. The imaging device 200 includes a camera body 250 having an imaging element 260 and a lens device 210 including an optical system 220 similar to any of the above-described embodiments 1 to 5. The lens device 210 and the camera body 250 may be configured as an integrated unit, or may be configured as detachable components. The camera body 250 may be a so-called single-lens reflex camera with a quick-turn mirror, or a so-called mirrorless camera without a quick-turn mirror. The imaging element 260 is a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that receives and photoelectrically converts the optical image formed by the optical system 220. Note that FIG. 12 shows only one optical system because two optical systems are arranged side by side in the depth direction.

[0084] The imaging device 200 of this embodiment includes the lens device 210, and is therefore small, high-performance, and low-cost, and is capable of performing stereoscopic imaging by using one imaging element to perform imaging using two optical systems.

[0085] The optical systems of the above-described embodiments are not limited to the digital still camera shown in FIG. 12, but can also be applied to various imaging devices such as broadcast cameras, cameras for silver halide film, and surveillance cameras.

[0086] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0087] L1 First lens group L2 Second lens group L3: Third lens group PR1 First Reflector Prism PR2 Second Reflector Prism

Claims

1. An optical system comprising, arranged in order from an object side to an image side, a first lens group having negative refractive power, a first reflecting member, a second lens group having positive refractive power and equipped with an aperture stop, a second reflecting member, and a third lens group having positive refractive power, When the focal length of the optical system is f, the focal length of the first lens group is f1, the focal length of the second lens group is f2, the focal length of the third lens group is f3, the refractive index of the material of the first reflecting member to the d-line is NPr, and the refractive index of the positive lens with the greatest refractive power among the positive lenses constituting the first lens group to the d-line is N1p, -1.27<(f1 / f) / Npr<-0.70 0.60<f2 / f3<1.60 1.78<N1p<2.20 An optical system characterized by satisfying the following conditional expression:

2. 4.80<f2 / f<10.50 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. 3. The optical system according to claim 1, wherein the first lens group includes two or more negative lenses and one or more positive lenses.

4. When the average value of the refractive index for the d-line of the negative lenses constituting the first lens group is N1Aave, 1.78<N1Aave<2.20 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the distance between the reflecting surfaces of the first reflecting member and the second reflecting member on the optical axis is LP, 1.00<f2 / LP<2.40 5. The optical system according to claim 1, wherein the following condition is satisfied:

6. When the distance between the reflecting surfaces of the first reflecting member and the second reflecting member on the optical axis is LP, 1.00<f3 / LP<2.20 6. The optical system according to claim 1, wherein the following condition is satisfied:

7. 1.78<Npr<2.20 7. The optical system according to claim 1, wherein the following condition is satisfied:

8. When the half angle of view (°) of the optical system is ω, 85.0°<ω<120.0° 8. The optical system according to claim 1, wherein the following condition is satisfied:

9. 9. The optical system according to claim 1, wherein the optical system comprises, in order from the object side to the image side, the first lens group, the first reflecting member, the second lens group, the second reflecting member, and the third lens group.

10. 10. A lens device comprising two optical systems, a first optical system as the optical system according to claim 1 and a second optical system as the optical system.

11. When the distance between the vertices of the lenses located closest to the object side in the two optical systems is Din and the distance between the vertices of the lenses located closest to the image side in the two optical systems is Dout, 0.05<Dout / Din<0.50 11. The lens device according to claim 10, wherein the following condition is satisfied:

12. 12. The lens device according to claim 11, wherein the two optical systems are arranged in parallel.

13. A lens device according to any one of claims 10 to 12; an imaging element that captures an optical image formed by the two optical systems.

14. 14. The imaging device according to claim 13, wherein the optical images formed by the two optical systems are captured by one of the imaging elements.

Images