Attachment optical system and imaging device

Abstract

To provide an attachment optical system that allows a user to arbitrarily change an imaging range and can perform stereo imaging with high image quality.SOLUTION: An attachment optical system allowing an imaging lens to be attached to an object side has two inflection optical systems arranged in parallel. The two inflection optical systems each include a first reflection member and a second reflection member. The inflection optical systems are each composed of a front group and a rear group arranged in order from the object side to an image side. The front group and the rear group are arranged at the maximum air gap from each other in each inflection optical system. At least either one of the first reflection member or the second reflection member is arranged between a surface having a refractive power on the most object side in the rear group and a surface having a refractive power on the most image side in the rear group in each of the two inflection optical systems.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an attachment optical system mounted between an interchangeable lens and an imaging apparatus, and is particularly suitable for stereo imaging.

Background Art

[0002] In recent years, observation devices and contents that provide a sense of presence, such as virtual reality (VR) and augmented reality (AR), have become increasingly abundant. Along with this, demand for imaging apparatuses for capturing videos used in such contents has been increasing. In particular, for diverse video expression, it is preferable that a user can arbitrarily select an imaging area to be captured, and it is also preferable that high-quality videos can be captured.

[0003] Patent Documents 1 and 2 disclose a stereo imaging optical system having an intermediate image. Further, Patent Document 3 discloses a relay optical system that relays a primary image plane of an interchangeable lens to a secondary image plane.

Prior Art Literature

Patent Literature

[0004]

Patent Literature 1

Patent Literature 2

Patent Literature 3

Summary of the Invention

Problem to be Solved by the Invention

[0005] However, the specifications of the stereo imaging optical systems described in Patent Documents 1 and 2 are each fixed to a wide-angle range, and there is no method other than cropping an image to expand the imaging range. For this reason, there are problems that image quality is degraded or post-imaging processing becomes complicated.

[0006] Furthermore, while the relay optical system described in Patent Document 3 allows for changing the imaging range by changing the interchangeable lens, it is an interchangeable back for video and therefore insufficient as a configuration suitable for a stereo optical system. Specifically, the baseline length of a stereo optical system is ideally about the width of a human eye, but the relay optical system in Patent Document 3 has the problem of having a baseline length that is too long.

[0007] The present invention aims to provide an attachment optical system that allows the user to arbitrarily change the imaging range and enables high-quality stereo imaging. [Means for solving the problem]

[0008] An attachment optical system as one aspect of the present invention is an attachment optical system on which an imaging lens can be attached to an object, wherein the attachment optical system has two bending optical systems arranged in parallel, each of the two bending optical systems includes a first reflecting member and a second reflecting member, each of the two bending optical systems is composed of a front group and a rear group arranged in order from the object side to the image side, the front group and the rear group are arranged with the maximum air gap between them, and at least one of the first reflecting member or the second reflecting member is arranged between the surface of the rear group of each of the two bending optical systems that has the refractive power closest to the object and the surface of the rear group that has the refractive power closest to the image. Furthermore, when the transverse magnification of each of the two bending optical systems is β, -0.75<β<-0.25 The following condition is satisfied It is characterized by the following.

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

[0010] According to the present invention, it is possible to provide an attachment optical system that allows the user to arbitrarily change the imaging range and enables high-quality stereo imaging. [Brief explanation of the drawing]

[0011] [Figure 1] It is a cross-sectional view of a stereo optical system composed of an interchangeable lens and the attachment optical system of Example 1. [Figure 2] It is a diagram schematically showing two image circles formed on an imaging surface. [Figure 3] It is an optical cross-sectional view of the attachment optical system of Example 1 with an ideal lens mounted thereon. [Figure 4] It is an aberration diagram of a relay image formed by the attachment optical system of Example 1 with an ideal lens mounted thereon. [Figure 5] It is an optical cross-sectional view of the attachment optical system of Example 2 with an ideal lens mounted thereon. [Figure 6] It is an aberration diagram of a relay image formed by the attachment optical system of Example 2 with an ideal lens mounted thereon. [Figure 7] It is an optical cross-sectional view of the attachment optical system of Example 3 with an ideal lens mounted thereon. [Figure 8] It is an aberration diagram of a relay image formed by the attachment optical system of Example 3 with an ideal lens mounted thereon. [Figure 9] It is an optical cross-sectional view of the attachment optical system of Example 4 with an ideal lens mounted thereon. [Figure 10] It is an aberration diagram of a relay image formed by the attachment optical system of Example 4 with an ideal lens mounted thereon. [Figure 11] It is a schematic diagram of an imaging apparatus. Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments of an attachment optical system and an imaging apparatus including the same according to the present invention will be described with reference to the accompanying drawings.

[0013] A method using a stereo imaging optical system is known as a common method for obtaining images that provide a sense of presence such as virtual reality (VR) and augmented reality (AR). In a stereo imaging optical system, two optical systems are arranged in parallel with respect to a subject. The stereo imaging optical system is an optical system that acquires distance information of a subject by utilizing the principle of triangular ranging and captures a three-dimensional image. Generally, as a stereo imaging optical system, stereo imaging is realized by arranging two image pickup devices or two imaging apparatuses in parallel and combining respective captured images. However, this method complicates the combining work. For example, since it is necessary to align the optical axes of the two imaging apparatuses with high accuracy, attention must be paid to the arrangement of these imaging apparatuses. In addition, since it is necessary to match the imaging timing between the two imaging apparatuses, it becomes necessary to synchronize imaging.

[0014] In order to improve the workability of these processes, an optical system that forms optical images by two optical systems on a single image pickup element is known. In an imaging apparatus using such an optical system, optical axis alignment is guaranteed by the imaging apparatus and imaging is also performed simultaneously, so the above-described work to be performed by a user is eliminated, and stereo imaging can be easily performed.

[0015] There are a plurality of such optical systems that enable stereo imaging with a single image pickup element, including the optical system disclosed in the above-mentioned patent documents. However, in any of the documents, specifications of the imaging lens are defined, and imaging can only be performed at a fixed imaging angle of view. On the other hand, as a user need, there is a demand for changing the imaging angle of view according to the imaging subject and the imaging scene. In order to meet such needs, attachment optical systems in respective embodiments are proposed.

[0016] The attachment optical system in each embodiment is an attachment optical system to which imaging lenses L1 and L2 can be attached to the object side. The attachment optical system in each embodiment has two bent optical systems A1 and A2 arranged in parallel with respect to a single image sensor. Each of the two bent optical systems A1 and A2 includes a first reflective member R11 (R21) and a second reflective member R12 (R22), which relay the optical images from imaging lenses L1 and L2 and form an image on the image sensor. By arranging these bent optical systems A1 and A2 in parallel, the optical images from two imaging lenses L1 and L2 can be formed side by side on a single image sensor, enabling stereo imaging with a single image sensor. Since the imaging lenses L1 and L2 arranged on the object side of the attachment optical system can be arbitrarily selected by the user, the imaging angle of view can be changed according to the imaging scene, expanding the range of expression for the user.

[0017] Figure 1 is a cross-sectional view of a stereo optical system consisting of interchangeable lenses, imaging lenses L1 and L2, and the attachment optical system of Embodiment 1. Although Figure 1 shows the attachment optical system of Embodiment 1 as a representative example, attachment optical systems of other embodiments may also be used. The attachment optical system has a bent optical system A1 and a bent optical system A2, and relays the optical images from imaging lenses L1 and L2 to form two images on the imaging surface IP. In Figure 1, imaging lenses L1 and L2 are indicated by arrows as aberration-free lenses that form an ideal image, but in actual use, there are one or more lenses. The bent optical system A1 has a first reflective member R11 and a second reflective member R12. The bent optical system A2 has a first reflective member R21 and a second reflective member R22. The first optical axis OP1 from the subject is bent by the first reflective members R11 and R21 to guide it to the second optical axis OP2, and the second optical axis is bent by the second reflective members R12 and R22 to guide it to the third optical axis OP3, thereby forming an optical image on the imaging plane IP with imaging lenses L1 and L2. In Figure 1, the optical axis is bent at 90 degrees by the first reflective members R11 and R21 and the second reflective members R12 and R22, but the bending angle is not limited to 90 degrees as long as the first optical axis OP1 and the third optical axis OP3 are parallel.

[0018] Figure 2 shows two image circles (regions where optical images are formed; effective image circles) IC1 and IC2 formed on the imaging surface IP. Image circle IC1 is formed by the imaging lens L1 and the bending optical system A1, and image circle IC2 is formed by the imaging lens L2 and the bending optical system A2. In this way, by using the attachment optical system of each embodiment, two images with parallax can be acquired with a single image sensor.

[0019] Images captured by a stereo optical system are observed using an observation optical system or display element. The distance Din between the first optical axes OP1 of the two bending optical systems A1 and A2 is preferably 40 mm to 80 mm, more preferably 50 mm to 65 mm. This is because the baseline length of the human eye is approximately 60 mm. By arranging the two bending optical systems A1 and A2 to match the interpupillary distance, a naturally stereoscopic image (video) can be obtained.

[0020] To ensure an appropriate baseline length for a stereo optical system, it is crucial to properly position the reflective elements R11, R21, R12, and R22 of the two bent optical systems A1 and A2. As described in the embodiments below, a large space must be provided on both the object side and the image side of each reflective element to eliminate vignetting of the light rays. Therefore, in order to keep the baseline length within the above range, it is necessary to shorten the distance between the first optical axis OP1 and the third optical axis OP3 by devising the configuration of the attachment optical system. Furthermore, in order to relay the optical images from the imaging lenses L1 and L2, the attachment optical system must have the desired imaging magnification and be able to correct aberrations well. For this reason as well, it is necessary to devise the configuration of the attachment optical system.

[0021] In each embodiment, the bent optical systems A1 and A2 are identical except for the reflection direction of the reflective members; therefore, the following description will refer to the bent optical system A1 as a representative example. Hereafter, when we say that the bent optical systems A1 and A2 are identical, it means that the lens configuration and other components are identical except for the reflection direction of the reflective members.

[0022] The bending optical system A1 in each embodiment is described below.

[0023] Figure 3 is an optical cross-sectional view of the imaging lens L1 and the bent optical system A1 of Example 1. Figure 4 is an aberration diagram of the relay image produced by the bent optical system A1 of Example 1 when the imaging lens L1 is focused at infinity. Figure 5 is an optical cross-sectional view of the imaging lens L1 and the bent optical system A1 of Example 2. Figure 6 is an aberration diagram of the relay image produced by the bent optical system A1 of Example 2 when the imaging lens L1 is focused at infinity. Figure 7 is an optical cross-sectional view of the imaging lens L1 and the bent optical system A1 of Example 3. Figure 8 is an aberration diagram of the relay image produced by the bent optical system A1 of Example 3 when the imaging lens L1 is focused at infinity. Figure 9 is an optical cross-sectional view of the imaging lens L1 and the bent optical system A1 of Example 4. Figure 10 is an aberration diagram of the relay image produced by the bent optical system A1 of Example 4 when the imaging lens L1 is focused at infinity.

[0024] In each optical cross-sectional view, the left side is the object side (front), and the right side is the image side (rear). In each optical cross-sectional view, IP is the image plane, and when the attachment optical system of each embodiment is used as the shooting 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 placed there. When the attachment optical system of each embodiment is used as the shooting optical system of a silver halide film camera, a photosensitive surface corresponding to the film surface is placed on the image plane IP.

[0025] In the spherical aberration diagram, Fno is the F-number and indicates the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, dS indicates the amount of astigmatism at the sagittal image plane, and dM indicates the amount of astigmatism at 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 at the g-line is shown. ω is the half-angle of view (°).

[0026] In the optical cross-sectional views of each embodiment, the reflective surface by the first reflective member R11 and the reflective surface by the second reflective member R12 are indicated by the reference numerals R11 and R12, respectively, and the bending of the optical axis by the reflective surfaces R11 and R12 is shown in an unfolded state. In each embodiment, the spacing between the reflective surfaces is ensured by assuming that the second optical axis OP2 is an optical axis perpendicular to the first optical axis OP1 and the third optical axis OP3. However, by further increasing the spacing between the reflective surfaces, it is also possible to reduce the reflection angle and shorten the baseline length as described above.

[0027] In the optical cross-sectional view of each embodiment, the imaging lens L1 is indicated by an arrow as an aberration-free, ideal imaging lens (ideal lens). In actual use, the imaging lens L1 has one or more lenses, and generally consists of multiple lens groups, having a desired focal length and back focus, similar to the interchangeable lenses of a single-lens reflex camera.

[0028] In each embodiment, the bent optical system A1 positioned on the image side of the imaging lens L1 includes a first reflective member R11 and a second reflective member R12. As described above, the two reflective members R11 and R12 bend the light rays from the subject, reducing the relay image of the imaging lens L1 and forming an image on the imaging surface IP.

[0029] In each embodiment, the bent optical system A1 has multiple lenses. In each embodiment, the bent optical system A1 consists of a front group A11 and a rear group A12, arranged sequentially from the object side to the image side. The front group A11 and the rear group A12 are separated by the maximum air gap in the bent optical system A1. In the bent optical system A1, at least one of the first reflective member R11 or the second reflective member R12 is positioned between the surface of the rear group A12 having the greatest refractive power on the object side and the surface of the rear group A12 having the greatest refractive power on the image side. In embodiments 1 and 4, the second reflective member R12 is positioned between the surface of the rear group A12 having the greatest refractive power on the object side and the surface of the rear group A12 having the greatest refractive power on the image side. In embodiment 2, the first reflective member R11 is positioned between the surface of the rear group A12 having the greatest refractive power on the object side and the surface of the rear group A12 having the greatest refractive power on the image side. In Example 3, the first reflective member R11 and the second reflective member R12 are positioned between the surface of the rear group A12 that has the greatest refractive power on the object side and the surface of the rear group A12 that has the greatest refractive power on the image side.

[0030] In each embodiment, the front group A11 has a positive refractive power. For miniaturization, the imaging lens L1 has an exit pupil on the object side of the imaging plane of the imaging lens L1, and in each embodiment, the position of the ideal lens is the exit pupil. The light rays emitted from the exit pupil are incident on the bending optical system A1 in such a way that the principal rays spread out, and by making the refractive power of the front group A11 of the bending optical system A1 positive, the effect of reducing the lens system of the rear group A12 is achieved.

[0031] In each embodiment, the front group A11 is composed of three or four spherical lenses. The front group A11 also includes at least one set of cemented lenses. This configuration allows for good correction of chromatic aberration and field curvature occurring in the bent optical system A1. Although the front group A11 is composed of three or more lenses in each embodiment, these aberrations can also be corrected with two aspherical lenses if aspherical lenses are used.

[0032] In each embodiment, the rear group A12 has a pupil conjugate to the exit pupil of the imaging lens L1 between the surface with the greatest refractive power on the object side and the surface with the greatest refractive power on the image side. By having a pupil in the rear group A12 in this way, symmetrical aberrations on either side of the pupil can be canceled, thus effectively correcting the field curvature, distortion, and chromatic aberration of the bent optical system A1. Furthermore, since on-axis and off-axis rays converge near this pupil, the width of the total rays becomes smaller. In other words, by placing the first reflective member R11 or the second reflective member R12 near this pupil, it is possible to reduce the reflective surface and shorten the baseline length to fit within the desired length mentioned above.

[0033] In Examples 1, 2, and 4, the reflective members R11 and R12 are miniaturized by positioning them on either side of the pupil within the rear group A12. It is preferable that these reflective members R11 and R12, positioned on either side of the pupil, be made of prisms with a refractive index of 1.5 or higher in order to shorten the optical path length. In Example 3, although the reflective members R11 and R12 are not positioned on either side of the pupil, miniaturization of the reflective members is achieved by positioning them near the pupil. Even in this case, the reflective members R11 and R12 are miniaturized as much as possible by positioning them between the surface of the rear group A12 with the greatest refractive power on the object side and the surface with the greatest refractive power on the image side.

[0034] Preferably, on the object side of the pupil, lenses with positive, positive, and negative refractive powers are arranged in that order from the object side, and on the image side of the pupil, lenses with negative, positive, and positive refractive powers are arranged in that order from the object side. By arranging the lenses in this way, which is a so-called Gaussian type configuration symmetrical with respect to the pupil, various aberrations such as field curvature and distortion can be corrected well. In Examples 1 and 4, three lenses with positive, positive, and negative refractive powers are arranged between the two reflective members R11 and R12 in that order from the object side. In Example 2, four lenses with negative, positive, positive, positive, and positive refractive powers are arranged between the two reflective members R11 and R12 in that order from the object side. By arranging the two reflective members R11 and R12 with respect to the pupil in this way, the number of lenses between the two reflective members R11 and R12 can be reduced, and the baseline length can be further shortened.

[0035] In each embodiment, the rear group A12 is constructed based on a Gaussian type. However, the configuration is not limited to this, as long as the reflective members R11 and R12 can be placed near the pupil within the rear group A12 and the number of lenses between the two reflective members R11 and R12 can be reduced. However, it is preferable to have five or fewer lenses between the two reflective members R11 and R12. This is because it becomes difficult to shorten the baseline length as the number of lenses increases.

[0036] On the other hand, in the configuration shown in Example 3, where two reflective members R11 and R12 are placed side by side on the object side of the Gaussian lens, the reflective members R11 and R12 become somewhat larger. However, the baseline length can be shortened by not placing a lens between the two reflective members R11 and R12. In this case, in order to shorten the air equivalent length as much as possible, it is preferable that the two reflective members R11 and R12 be made of prisms with a refractive index of 1.5 or higher.

[0037] In each embodiment, the focusing mechanism of the imaging lenses L1 and L2 attached to the object side of the attachment optical system can be used when focusing from infinity to near. However, if the imaging lenses L1 and L2 have different focal points, a condition known as astigmatism will occur where the left and right eyes have different focal points during observation. Therefore, it is preferable to equip the attachment optical system with a focusing mechanism. By fixing the focal positions of imaging lenses L1 and L2 to infinity and simultaneously driving the same lenses in the optical axis direction in the two bent optical systems A1 and A2, the focal positions of the left and right eyes can be adjusted simultaneously.

[0038] Next, we will describe the conditions that the attachment optical system of each embodiment should preferably satisfy.

[0039] The attachment optical system of each embodiment preferably satisfies one or more of the following conditions (1) to (3).

[0040] 0.05 <Dout / Din<0.50 ···(1) 0.20 <fF / |fR|<2.00 ···(2) -0.75 < β < -0.25 ···(3) Here, Din is the distance between the vertices of the lens surfaces closest to the object in the two bent optical systems A1 and A2. Dout is the distance between the vertices of the lens surfaces closest to the image in the two bent optical systems A1 and A2. fF is the focal length of the front group A11. fR is the focal length of the rear group A12. β is the transverse magnification of the two bent optical systems A1 and A2, respectively.

[0041] Condition (1) specifies the distance between the object-side lens surfaces and the image-side lens surfaces of the two bending optical systems A1 and A2. Satisfying condition (1) makes it possible to miniaturize the entire device while ensuring a sufficient baseline length. If the value falls below the lower limit of condition (1), the distance between the vertices of the image-side lens surfaces becomes too small, causing the lenses on the third optical axis OP3 of the two bending optical systems A1 and A2 to interfere with each other. Alternatively, the distance between the vertices of the object-side lens surfaces becomes too large. In this case, it becomes difficult to capture a stereoscopic image that looks natural to the human eye. If the value exceeds the upper limit of condition (1), the distance between the vertices of the object-side lens surfaces becomes too small, making it impossible to ensure a sufficient baseline length. In this case as well, it becomes difficult to capture a stereoscopic image that looks natural to the human eye. Alternatively, the distance between the vertices of the image-side lens surfaces becomes too large, causing the entire device to become larger.

[0042] Conditional equation (2) specifies the ratio of the focal lengths of the front group A11 and the rear group A12 in the bent optical systems A1 and A2, respectively. If the value falls below the lower limit of conditional equation (2), the refractive power of the front group A11 becomes strong, which is advantageous for miniaturizing the attachment optical system. However, in order to obtain the desired lateral magnification, the refractive power of the rear group A12 also needs to be strong, which increases the angle of the light beam and makes aberration correction difficult. If the value exceeds the upper limit of conditional equation (2), the refractive power of the front group A11 becomes too weak, causing the lens system of the rear group A12 to become larger, and consequently, the reflective elements included in the rear group A12 to become too large. As a result, the distance between the vertices of the lens surface closest to the object becomes too large. In this case, it becomes difficult to capture a natural-looking stereoscopic image to the human eye.

[0043] Conditional equation (3) specifies the lateral magnification of the bending optical systems A1 and A2, respectively. Assuming the size of the imaging surface IP is fixed, the lateral magnification of the bending optical systems A1 and A2 affects whether an image is formed on the imaging surface IP depending on which region of the imaging lenses L1 and L2 the light beam passes through. Good aberration correction cannot be obtained in the peripheral areas of imaging lenses L1 and L2, but when the lateral magnification of the bending optical systems A1 and A2 is small, an image is formed on the imaging surface IP by the light beam that passes through a relatively narrow region centered on the optical axis of imaging lenses L1 and L2. Since the light beam in the peripheral areas of imaging lenses L1 and L2 is not used, it is preferable for the lateral magnification of the bending optical systems A1 and A2 to be small. On the other hand, when the lateral magnification of the bending optical systems A1 and A2 is small, the angle of view that can be captured by imaging lenses L1 and L2 becomes narrower, so it is necessary to set an appropriate magnification.

[0044] Furthermore, reducing the lateral magnification of the folded optical systems A1 and A2 increases their refractive power, allowing for a shorter optical axis distance and a more compact configuration. However, drastically reducing the lateral magnification increases the angle of the light beam incident on the relay lens system, making aberration correction difficult. Conversely, increasing the lateral magnification of the folded optical systems A1 and A2 increases the overall size of the lens system to maintain good aberration correction. Alternatively, since the light beam passes through a relatively wide area of ​​the imaging lenses L1 and L2 before being incident on the imaging plane IP, the aberration correction state of the imaging lenses L1 and L2 significantly affects the imaging performance. Therefore, conditional equation (3) defines a desirable lateral magnification for the folded optical system in a case where the size of the imaging plane IP is fixed to approximately that of a full-frame sensor. If the value falls below the lower limit of conditional equation (3), the angle of the light beam incident on the folded optical systems A1 and A2 increases, making aberration correction difficult. If the upper limit of condition (3) is exceeded, the folded optical systems A1 and A2 will increase in size in order to maintain a good aberration correction state, and the aberration correction state of the imaging lenses L1 and L2 will have a significant impact on the imaging performance.

[0045] Furthermore, in order to realize a smaller and higher-performance attachment optical system, it is more preferable that the numerical ranges of conditional equations (1) to (3) be within the range of conditional equations (1a) to (3a) below.

[0046] 0.06 <Dout / Din<0.40 ···(1a) 0.21 <fF / |fR|<1.80 ···(2a) -0.70 < β < -0.35 ···(3a) Furthermore, it is even more preferable that the numerical ranges of conditional expressions (1) to (3) be within the ranges of the following conditional expressions (1b) to (3b).

[0047] 0.08 <Dout / Din<0.30 ···(1b) 0.22 <fF / |fR|<1.60 ···(2b) -0.65 < β < -0.45 ···(3b) In Examples 1 to 3, the front group A11 is positioned on the object side of the focal position of the imaging lens L1 in order to further miniaturize the attachment optical system. Interchangeable lenses for SLR or mirrorless cameras have a predetermined flange back distance from the lens mount surface to the imaging surface IP. By positioning the lens in this space, the overall length of the attachment optical system can be shortened, resulting in miniaturization. On the other hand, in Example 4, the front group A11 is positioned on the image side of the focal position of the imaging lens L1. In the arrangement of the front group A11 in Example 4, a diffuser can be placed at the focal position of the imaging lens L1. By placing a diffuser, the conjugate relationship between the exit pupil of the imaging lens L1 and the pupil of the bent optical system A1 is relaxed, improving the degree of design freedom. This makes it possible to realize an attachment optical system that is smaller or has higher specifications.

[0048] The numerical values ​​corresponding to Examples 1 to 4 are shown below.

[0049] In the surface data for each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the on-axial spacing (distance along the optical axis) between the m-th 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 νd represents the Abbe number of the optical element. Note that the Abbe number νd of a certain material is expressed as νd = (Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the Fraunhofer lines d line (587.6 nm), F line (486.1 nm), and C line (656.3 nm). The effective diameter refers to the maximum diameter of the region (effective area) through which the effective light beam contributing to imaging passes within the lens surface.

[0050] 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 BF" is the distance along the optical axis from the final lens surface with refractive power (the lens surface closest to the image) to the paraxial image plane, expressed in terms of air equivalent length. "Total lens length" is the length obtained by adding the back focus to the distance along the optical axis from the frontmost lens surface (the lens surface closest to the object) to the final surface of the zoom lens. "Lens group" includes not only cases where it is composed of multiple lenses, but also cases where it is composed of a single lens. (Numerical Example 1) Camera lens Focal length 50.00 F-number 4.67 Image height 14.25 Attachment Optical System Focal length -95.59 Front group focal length 41.11 Rear group focal length 32.67 Horizontal magnification -0.60 Lens length: 96.08 Surface data Face number rd nd νd Effective diameter 0 45.52 1 -29.234 1.20 1.51633 64.1 26.00 2 126.496 6.42 2.00069 25.5 29.10 3 -39.493 5.17 30.00 4 59.487 7.41 1.96300 24.1 31.70 5 -44.100 1.40 1.51823 58.9 31.30 6 32.163 18.47 28.10 7 ∞ 15.10 42.40 8 30.953 5.38 1.88300 40.8 22.70 9 -92.127 0.10 21.50 10 16.091 4.15 1.88300 40.8 17.40 11 43.500 0.69 14.70 12 1356.279 0.80 1.77830 23.9 14.50 13 9.045 2.75 12.00 14 ∞ 6.70 1.51633 64.1 11.90 15 ∞ 6.70 1.51633 64.1 19.00 16 ∞ 1.66 10.00 17 -9.937 1.00 1.63980 34.5 10.00 18 147.010 0.75 10.70 19 -27.958 3.05 1.88300 40.8 10.80 20 -14.467 0.10 11.90 21 76.301 3.58 1.49700 81.5 12.90 22 -14.310 0.10 13.80 23 28.420 3.40 1.49700 81.5 14.90 24 -353.815 30.02 15.00 Image plane ∞ Shooting lens + attachment optics Focal length -30.04 F-number 2.80 Half-angle (°): 15.89 Image height 8.55 BF 30.02 (Numerical Example 2) Camera lens Focal length 50.00 F-number 4.67 Image height 14.25 Attachment Optical System Focal length -81.05 Front group focal length 120.36 Rear group focal length 530.73 Horizontal magnification -0.60 Lens length: 131.88 Surface data Face number rd nd νd Effective diameter 0 36.80 1 -22.794 4.00 2.00100 29.1 22.20 2 -16.842 0.30 23.80 3 -16.247 1.20 1.53172 48.8 23.70 4 90.120 5.00 2.00100 29.1 27.40 5 -64.622 28.35 28.10 6 307.190 7.20 1.95375 32.3 37.70 7 -43.755 1.40 1.53172 48.8 38.10 8 125.881 0.10 37.60 9 74.658 4.55 1.88300 40.8 37.70 10 -195.909 23.15 37.40 11 51.767 3.20 1.88300 40.8 22.20 12 2684.644 0.10 21.20 13 16.068 4.20 1.95375 32.3 18.10 14 39.361 1.05 15.50 15 79.949 0.80 1.80809 22.8 13.90 16 8.457 2.70 11.10 17 ∞ 7.25 1.51633 64.1 10.60 18 ∞ 7.25 1.51633 64.1 20.60 19 ∞ 1.55 8.70 20 -11.043 1.00 1.68430 26.8 8.60 21 -70.466 0.23 8.90 22 -30.444 4.00 1.88300 40.8 8.90 23 -14.396 0.10 11.80 24 162.431 2.95 1.49700 81.5 13.10 25 -17.422 0.10 13.90 26 27.834 3.25 1.59522 67.7 15.00 27 646.299 0.10 15.00 28 ∞ 8.40 1.51633 64.1 15.10 29 ∞ 8.40 1.51633 64.1 23.80 30 ∞ 17.33 15.90 Image plane ∞ Shooting lens + attachment optics Focal length -30.09 F-number 2.80 Half-angle (°): 15.86 Image height 8.55 BF 17.33 (Numerical Example 3) Camera lens Focal length 50.00 F-number 3.50 Image height 14.25 Attachment Optical System Focal length -73.23 Front group focal length 166.26 Rear group focal length -343.44 Horizontal magnification -0.60 Lens length: 192.77 Surface data Face number rd nd νd Effective diameter 0 39.86 1 -24.693 4.37 1.95375 32.3 24.04 2 -17.721 0.30 25.54 3 -17.166 1.20 1.48749 70.2 25.51 4 62.529 4.92 2.00100 29.1 29.09 5 -138.500 35.59 29.52 6 884.609 8.50 1.96300 24.1 45.24 7 -40.255 1.40 1.54814 45.8 45.50 8 52.677 3.48 44.48 9 127.425 6.50 1.90043 37.4 44.71 10 -118.752 8.33 44.81 11 ∞ 21.13 1.51633 64.1 42.00 12 ∞ 21.13 1.51633 64.1 59.76 13 ∞ 0.00 34.56 14 ∞ 17.38 1.51633 64.1 34.56 15 ∞ 17.38 1.51633 64.1 49.16 16 ∞ 0.10 28.44 17 26.223 5.42 1.72916 54.7 27.38 18 -931.274 0.72 26.43 19 17.533 6.58 1.49700 81.5 20.89 20 -197.011 0.10 16.88 21 -141.451 0.80 1.86966 20.0 16.76 22 11.189 14.40 13.59 23 -12.411 1.00 1.68430 26.8 13.44 24 -191.115 0.66 15.15 25 -46.049 4.00 1.94594 18.0 15.32 26 -19.523 0.10 17.12 27 358.638 4.00 1.53775 74.7 18.00 28 -18.820 0.10 18.36 29 29.467 3.18 1.59522 67.7 18.00 30 88.228 34.75 17.80 Image plane ∞ Shooting lens + attachment optics Focal length -30.11 F-number 2.10 Half-angle (°): 15.85 Image height 8.55 BF 34.75 (Numerical Example 4) Camera lens Focal length 50.00 F-number 2.80 Image height 14.25 Attachment Optical System Focal length -220.42 Front group focal length 60.36 Rear group focal length 39.44 Horizontal magnification -0.60 Lens length: 145.30 Surface data Face number rd nd νd Effective diameter 0 65.00 1 -33.333 1.40 1.59270 35.3 37.20 2 281.995 12.00 1.95906 17.5 45.30 3 -35.412 10.00 47.00 4 499.448 1.40 1.72825 28.5 45.10 5 26.958 16.00 1.65160 58.5 43.90 6 -133.973 23.30 44.00 7 ∞ 23.30 65.90 8 25.441 8.84 1.75500 52.3 34.50 9 -487.463 0.10 33.00 10 19.827 3.73 1.77250 49.6 24.30 11 43.426 1.65 22.40 12 -1519.289 0.80 1.89286 20.4 21.80 13 13.306 3.65 17.30 14 ∞ 9.00 1.51633 64.1 17.10 15 ∞ 9.00 1.51633 64.1 25.50 16 ∞ 2.10 14.80 17 -15.890 1.00 1.86966 20.0 14.80 18 165.637 1.30 16.40 19 -53.263 3.03 1.95375 32.3 16.90 20 -24.054 0.10 18.30 21 116.951 3.90 1.95906 17.5 19.70 22 -25.621 0.10 20.40 23 24.154 8.60 1.77250 49.6 21.10 24 -20.963 1.00 1.80810 22.8 19.80 25 30.816 23.13 18.30 Image plane ∞ Shooting lens + attachment optics Focal length -30.15 F-number 1.68 Half-angle (°): 15.83 Image height 8.55 BF 23.13 The various values ​​in each numerical example are summarized in Table 1 below.

[0051] [Table 1]

[0052] [Imaging device] Next, an example of an imaging device using the attachment optical system shown in each embodiment as the imaging optical system will be described with reference to Figure 11. Figure 11 is a schematic diagram of the main parts of a camera (imaging device) equipped with the attachment optical system of each embodiment.

[0053] In Figure 11, 20 is the camera body, and 21 is the imaging optical system composed of one of the attachment optical systems described in Examples 1 to 4. 22 and 23 are interchangeable lenses that are mounted on an interchangeable-lens camera, and the optical image from these interchangeable lenses is formed on a single solid-state image sensor on the camera body 20 by the attachment optical system 21. The interchangeable lenses 22 and 23 are imaging lens systems used in imaging devices such as video cameras, digital cameras, and silver halide film cameras. The subject image formed on the solid-state image sensor can be observed through the liquid crystal display panel or viewfinder of the camera body 20.

[0054] By applying the attachment optical system 21 of the present invention to an imaging device such as an interchangeable-lens camera, the user can arbitrarily change the imaging range and perform high-quality stereo imaging.

[0055] Each of the above embodiments includes the following configurations. (Composition 1) An attachment optical system on which an imaging lens can be attached to the object side, The aforementioned attachment optical system has two bent optical systems arranged in parallel, Each of the two bending optical systems includes a first reflecting member and a second reflecting member. Each of the two aforementioned bending optical systems consists of a front group and a rear group arranged sequentially from the object side to the image side, and the front group and the rear group are positioned with the maximum air gap between them in each bending optical system. An attachment optical system characterized in that at least one of the first reflective member or the second reflective member is disposed between the surface of the rear group of each of the two bending optical systems that has the refractive power closest to the object and the surface of the rear group that has the refractive power closest to the image. (Configuration 2) In the two bending optical systems described above, let Din be the distance between the vertices of the lens surfaces closest to the object, and let Dout be the distance between the vertices of the lens surfaces closest to the image. 0.05 <Dout / Din<0.50 The attachment optical system according to configuration 1, characterized in that it satisfies the following conditional expression. (Composition 3) The attachment optical system according to configuration 1 or 2, characterized in that the front group has a positive refractive power. (Composition 4) When the focal length of the front group is fF and the focal length of the rear group is fR, 0.20 <fF / |fR|<2.00 An attachment optical system according to any one of configurations 1 to 3, characterized by satisfying the following conditional expression. (Composition 5) When the transverse magnification of each of the two aforementioned refraction optical systems is β, -0.75 < β < -0.25 An attachment optical system according to any one of configurations 1 to 4, characterized by satisfying the following conditional expression. (Composition 6) The attachment optical system according to any one of configurations 1 to 5, characterized in that the front group is positioned on the object side of the focal position of the imaging lens. (Composition 7) The attachment optical system according to any one of configurations 1 to 5, characterized in that the front group is positioned on the image side of the focal position of the imaging lens. (Composition 8) The attachment optical system according to any one of configurations 1 to 7, characterized in that five or fewer lenses are arranged between the first reflecting member and the second reflecting member. (Composition 9) The attachment optical system according to any one of configurations 1 to 8, characterized in that the front group consists of three or four spherical lenses. (Composition 10) The attachment optical system according to any one of configurations 1 to 9, characterized in that the front group includes a set of cemented lenses. (Composition 11) The attachment optical system according to any one of configurations 1 to 10, characterized in that the two bending optical systems are identical to each other. (Composition 12) An attachment optical system as described in any of configurations 1 to 11, An imaging device characterized by having an image sensor that captures an optical image formed by the two bending optical systems. (Composition 13) The imaging apparatus according to configuration 12, characterized in that the two bending optical systems are arranged in parallel with respect to the image sensor.

[0056] Although 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 its gist. [Explanation of Symbols]

[0057] Flexible optical system A1(A2) First reflective element R11 (R21) Second reflective element R12 (R22) Front group A11 Rear group A12

Claims

1. An attachment optical system on which an imaging lens can be attached to the object side, The aforementioned attachment optical system has two bent optical systems arranged in parallel, Each of the two bending optical systems includes a first reflecting member and a second reflecting member. Each of the two aforementioned bending optical systems consists of a front group and a rear group arranged sequentially from the object side to the image side, and the front group and the rear group are positioned with the maximum air gap between them in each bending optical system. At least one of the first reflective member or the second reflective member is positioned between the surface of the rear group of each of the two bending optical systems that has the refractive power closest to the object and the surface of the rear group that has the refractive power closest to the image. When the transverse magnification of each of the two aforementioned refraction optical systems is β, －０．７５＜β＜－０．２５ An attachment optical system characterized by satisfying the following conditional equation.

2. When Din is the distance between the vertices of the lens surfaces closest to the object in the two bending optical systems, and Dout is the distance between the vertices of the lens surfaces closest to the image in the two bending optical systems, 0.05<Dout / Din<0.50 The attachment optical system according to claim 1, characterized in that it satisfies the following condition.

3. The attachment optical system according to claim 1, characterized in that the front group has a positive refractive power.

4. When the focal length of the front group is fF and the focal length of the rear group is fR, 0.20<fF / |fR|<2.00 The attachment optical system according to claim 1, characterized in that it satisfies the following condition.

5. The attachment optical system according to claim 1, characterized in that the front group is positioned closer to the object than the focal position of the imaging lens.

6. The attachment optical system according to claim 1, characterized in that the front group is positioned on the image side of the focal position of the imaging lens.

7. The attachment optical system according to claim 1, characterized in that five or fewer lenses are arranged between the first reflective member and the second reflective member.

8. The attachment optical system according to claim 1, characterized in that the front group consists of three or four spherical lenses.

9. The attachment optical system according to claim 1, characterized in that the front group includes a set of cemented lenses.

10. The attachment optical system according to claim 1, characterized in that the two bending optical systems are identical to each other.

11. An attachment optical system according to any one of claims 1 to 10, An imaging device characterized by having an image sensor that captures an optical image formed by the two bending optical systems.

12. The imaging apparatus according to claim 11, characterized in that the two bent optical systems are arranged in parallel with respect to the image sensor.

Images