Lens device and image capturing device

Abstract

To suppress distortion aberration while avoiding an increase in the size of the entire optical system by adding another optical system to a master optical system.SOLUTION: An optical system disclosed herein comprises a first optical system LA and a second optical system LC that can be removably inserted into an image side of the most object-side surface of the first optical system. The second optical system is configured to reduce distortion aberration at the maximum image height by 10% or more when inserted into the optical system compared with when not inserted. The second optical system satisfies a condition expressed as: 0.5≤βc≤1.3, where βc represents a lateral magnification of the optical system,.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a lens device suitable for an imaging device. [Background technology]

[0002] As a method for obtaining a low-distortion wide-angle lens from a fisheye lens, Patent Document 1 discloses a method for converting the projection method of a fisheye lens to a general projection method by placing an aspheric dome lens with negative refractive power on the object side of the fisheye lens (master optical system). Patent Document 2 discloses a method for changing the projection method by exchanging an intermediate portion between the object side and the image side of the optical system.

[0003] In the general projection method, when the focal length of the lens is f, the angle that the light from the object makes with the optical axis is θ, and the image height of the object is y, y=ftanθ(a) In addition, the amount of distortion D (%) in the general projection method is expressed as follows, where yp is the actual image height and y0 is the ideal image height: D = 100 × (yP-y0) / y0 (b) It is expressed as:

[0004] In order to obtain an angle of view close to 180° with a fisheye lens, the amount of distortion expressed by equation (b) needs to be increased. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2008-197541 A [Patent Document 2] JP 2019-174753 A Summary of the Invention [Problem to be solved by the invention]

[0006] Placing a dome lens on the object side of a fisheye lens as in Patent Document 1 leads to an increase in the size of the entire optical system. Furthermore, the method of replacing the intermediate part of the optical system as in Patent Document 2 requires replacement work and the configuration to enable replacement becomes complicated.

[0007] The present invention provides a lens device that can suppress distortion while avoiding an increase in the size of the entire optical system by adding another optical system to the master optical system. [Means for solving the problem]

[0008] An optical system according to one aspect of the present invention includes a first optical system and a second optical system that can be inserted and removed from the surface of the first optical system closest to the object toward the image side. The second optical system is configured such that, when inserted into the optical system, distortion at the maximum image height is reduced by 10% or more compared to when not inserted. When the lateral magnification of the second optical system is βc, 0.5≦βc≦1.3 The optical system is characterized in that it satisfies the following conditions. An imaging device including the optical system also constitutes another aspect of the present invention. A second optical system as yet another aspect of the present invention is a second optical system that can be inserted and removed from a surface of the first optical system closest to the object toward the image side, and the second optical system is configured such that, when inserted into the first optical system, distortion at the maximum image height is reduced by 10% or more compared to when not inserted, When the lateral magnification of the second optical system is βc, 0.5≦βc≦1.3 The present invention is characterized in that it satisfies the following conditions. Effect of the Invention

[0009] According to the present invention, by adding the second optical system on the image side of the surface of the first optical system closest to the object, it is possible to suppress distortion while avoiding an increase in the size of the entire optical system. [Brief description of the drawings]

[0010] [Figure 1]3A is a cross-sectional view of the optical system of Example 1 at the wide-angle end, and FIG. 3B is a cross-sectional view of the optical system at the telephoto end with an additional lens group inserted. [Diagram 2] 1A to 1D are aberration diagrams of the optical system of Numerical Example 1 at (A) the wide-angle end, (B) the intermediate zoom position, (C) the telephoto end, and (D) the telephoto end with the additional lens group inserted. [Diagram 3] 11A is a cross-sectional view of the optical system of Example 2 at the wide-angle end, and FIG. 11B is a cross-sectional view of the optical system at the telephoto end with an additional lens group inserted. [Figure 4] 11A to 11D are aberration diagrams of the optical system of Numerical Example 2 at (A) the wide-angle end, (B) the intermediate zoom position, (C) the telephoto end, and (D) the telephoto end with the additional lens group inserted. [Diagram 5] 11A is a cross-sectional view of the optical system of Example 3 when the additional lens group is not inserted, and FIG. 11B is a cross-sectional view of the optical system of Example 3 when the additional lens group is inserted. [Figure 6] 11A and 11B are aberration diagrams of the optical system of Numerical Example 3 when (A) the additional lens group is not inserted and (B) the additional lens group is inserted. [Figure 7] 11A is a cross-sectional view of the optical system of Example 4 when the additional lens group is not inserted, and FIG. 11B is a cross-sectional view of the optical system of Example 4 when the additional lens group is inserted. [Figure 8] 11A and 11B are aberration diagrams of the optical system of Numerical Example 4 when (A) the additional lens group is not inserted and (B) the additional lens group is inserted. [Figure 9] 13A is a cross-sectional view of the optical system of Example 5 in a wide-angle focal state, FIG. 13B is a cross-sectional view of the optical system in a telephoto focal state, and FIG. 13C is a cross-sectional view of the optical system in a telephoto focal state with an additional lens group inserted. [Figure 10] 11A to 11C are aberration diagrams of the optical system of Numerical Example 5 in (A) the wide-angle side focal state, (b) the telephoto side focal state, and (c) the telephoto side focal state with the additional lens group inserted. [Figure 11] FIG. 4 is a diagram illustrating the definition of an aspheric amount. [Figure 12] FIG. 1 is a schematic diagram of an imaging device including the optical system according to Examples 1 to 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, prior to the detailed description of embodiments 1 to 6, matters common to the embodiments will be described.

[0012] The optical system of each embodiment is an imaging lens used in various imaging devices such as digital still cameras, video cameras, broadcast cameras, surveillance cameras, silver halide film cameras, etc. The optical system of each embodiment can also be used as a projection optical system for an image projection device (projector).

[0013] Fisheye lenses with a total angle of view close to 180° are designed to produce large distortion in the general projection method (f tan θ system). Methods for reducing distortion in fisheye lenses include limiting the angle of view of the fisheye lens itself to the telephoto end, i.e. performing an operation equivalent to zooming, or adding an aspherical lens (front converter) that suppresses distortion to the object side of the fisheye lens (master optical system). However, performing an operation equivalent to zooming will significantly reduce the angle of view from 180°, making it impossible to obtain the required angle of view. Also, because the diameter of the front converter itself is large, adding it will make the entire lens larger.

[0014] For this reason, in each embodiment, an additional lens group as a second optical system for correcting distortion can be added (inserted) in the area on the image side of the master optical system, which is the first optical system, thereby suppressing distortion without significantly reducing the angle of view and avoiding an increase in the size of the entire optical system.

[0015] 1(a), (b), 3(a), (b), 5(a)-(c), 7(a)-(c), and 9(a)-(c) show the optical systems of Examples 1-6, respectively. 1(a) and 3(a) show the configurations of the optical systems of Examples 1 and 2 as zoom lenses at the wide-angle end and in the non-inserted state of the additional lens group. 1(b) and 3(b) show the configurations of the optical systems of Examples 1 and 2 at the telephoto end and in the inserted state of the additional lens group. 5(a) and 7(a) show the configurations of the optical systems of Examples 3 and 4 as single focal length lenses at the non-inserted state of the additional lens group. 5(b) and 7(b) show the configurations of the optical systems of Examples 3 and 4 as double focal length switching lenses at the wide-angle side focal length and in the non-inserted state of the additional lens group. 9(a) shows the configuration of the optical system of Example 5 as a bifocal switching lens at the wide-angle side focal length and in the non-inserted state of the additional lens group. Fig. 9(b) shows the configuration of the optical system of Example 5 in a telephoto focal state with the additional lens group not inserted. Fig. 9(c) shows the configuration of the optical system of Example 5 in a telephoto focal state with the additional lens group inserted.

[0016] In each figure, the left side is the object side, and the right side is the image side. Li (i=1, 2, 3, ...) indicates the i-th lens group (i-th lens group) when counting from the object side. The lens group is composed of one or more lenses. The lens group may include an aperture stop. The lens group in a zoom lens is a group of one or more lenses that move together during zooming between the wide-angle end and the telephoto end. That is, the spacing between adjacent lens groups changes during zooming. In addition, the wide-angle end and the telephoto end respectively indicate the zoom states of the maximum angle of view (shortest focal length) and the minimum angle of view (maximum focal length) when the lens group that moves during zooming is located at both ends of the range that can be moved mechanically or controlled on the optical axis.

[0017] SP denotes the aperture stop, and IP denotes the image plane. The imaging surface (light receiving surface) of the image sensor and the film surface (photosensitive surface) of the silver halide film are located on the image plane IP. The lens groups marked with FOCUS move in the direction of the arrow in the diagram when focusing from infinity to close range. For zoom lenses, the movement trajectory of the lens group when zooming from the wide-angle end to the telephoto end is shown below the lens group that moves during zooming.

[0018] The additional lens group LC in each embodiment is an optical system that can be inserted and removed (added and removed) on the image side (for example, on the image side of the aperture stop SP) of the surface closest to the object of the master optical system LA. The additional lens group LC may be inserted and removed into the space within the master optical system LA, or may be inserted and removed as a rear converter into a space on the image side of the surface closest to the image of the master optical system LA.

[0019] Moreover, the additional lens group LC in each embodiment has at least one aspheric surface as a lens surface. In general, it is effective to correct distortion at a position where off-axis rays are high. For this reason, in each embodiment, a lens where off-axis rays are high near the image side is provided with an aspheric surface whose peripheral portion within the effective diameter has a negative aspheric amount, thereby effectively correcting negative distortion. Moreover, it is preferable that the aspheric surface has an inflection point where the refractive power changes from positive to negative.

[0020] FIG. 11 shows the aspheric amount Ar in each embodiment. The aspheric amount Ar is the maximum deviation amount of the aspheric surface Ra from the reference spherical surface Rref. The radius (curvature radius) of the reference spherical surface Rref is the radius of the sphere determined by the apex of the aspheric surface Ra and the effective diameter of the light beam. The deviation direction of the aspheric surface Ra from the reference spherical surface Rref is defined as a positive aspheric amount when the direction is a direction in which a medium is added to the reference spherical surface Rref, and a negative aspheric amount when the direction is a direction in which the medium is removed. For example, the aspheric surface Ra shown in FIG. 11 has a positive aspheric amount. In addition, in an aspheric lens in which both the object side and the image side are aspheric, the sum of the aspheric amounts of both sides is the aspheric amount of the aspheric lens.

[0021] Here, we will explain how to determine whether the aspheric amount is positive or negative from lens data (numerical data) in various documents or from an actual lens, and how to specifically calculate the aspheric amount. To determine whether the aspheric amount is positive or negative or to calculate the aspheric amount, it is first necessary to find the radius of the reference spherical surface, and in order to obtain the radius of the reference spherical surface, it is necessary to obtain the effective beam diameter.

[0022] If the effective diameter is not listed in the lens data, the drawing magnification of the cross-sectional view can be calculated from the actual optical length on the cross-sectional view of the optical system and the optical length indicated by the numerical data, and the effective diameter can be obtained by multiplying the actual diameter of the curved part on the cross-sectional view by the drawing magnification. Depending on the optical tool, the diameter of the curved part on the cross-sectional view is set to be slightly larger than the actual effective diameter of the beam, but this method is effective for determining whether the aspheric amount is positive or negative and for obtaining a rough estimate of the aspheric amount.

[0023] In each embodiment, the additional lens group LC has a weak positive refractive power. A teleconverter or the like that can be arranged on the image side of a general interchangeable lens has a relatively strong negative refractive power, thereby extending the focal length of the entire optical system to the telephoto end side. In each embodiment, in order to maintain the angle of view as wide as possible regardless of whether the additional lens group LC is inserted or removed, it is desirable to set the refractive power of the additional lens group LC to be weak, and it is particularly desirable for the additional lens group LC as a whole to have a positive refractive power.

[0024] In each embodiment, the additional lens group LC is made up of a plurality of lenses. In order to correct distortion and curvature of field, it is desirable to make the additional lens group LC up of two or more lenses.

[0025] Furthermore, in each embodiment, the additional lens group LC is configured so that, when inserted into the optical system, distortion at the maximum image height H is reduced by 10% or more compared to when not inserted. When the lateral magnification of the additional lens group LC is βc, the following condition of formula (1) is satisfied.

[0026] 0.5≦βc≦1.3 (1) The condition of formula (1) indicates an appropriate range of the lateral magnification of the additional lens group LC when inserted into the master optical system LA in order to effectively correct distortion by the additional lens group LC. If βc exceeds the upper limit of formula (1), the focal length of the entire optical system consisting of the master optical system LA and the additional lens group LC increases, and the amount of negative distortion at the maximum image height decreases, but the angle of view becomes too narrow to maintain the required wide angle of view, which is not preferable. In addition, it becomes necessary to strengthen the refractive power of the additional lens group LC in the negative direction, which makes it difficult to correct aberrations while maintaining a small and lightweight structure, which is not preferable. If βc falls below the lower limit of formula (1), the positive refractive power of the additional lens group LC becomes too strong, which makes it difficult to suppress the field curvature aberration, which is not preferable. In addition, it becomes necessary to increase the number of lenses constituting the additional lens group LC in order to correct aberrations, which is not preferable from the viewpoint of reducing size and weight.

[0027] As described above, by providing the additional lens group LC in the image-side region of the master optical system LA, it is possible to suppress distortion while avoiding an increase in size of the entire optical system having a wide angle of view, such as a fisheye region.

[0028] It is preferable that the optical system of each embodiment satisfies at least one of the conditions of the following expressions (2) to (8).

[0029] 4≦fc / fmc≦200 (2) 0.1≦skc / Tc≦1.2 (3) 2≦TTLm / Tc≦10 (4) 0.9≦Yc / Ymm≦3.0 (5) 0.3≦θc / θmm≦1.2 (6) 15≦Dist_c-Dist_m≦80 (7) -12≦fc / fLA1≦-1 (8) In the formulas (2) to (8), fc is the focal length of the additional lens group LC, and fmc is the focal length of the master optical system LA alone in a state in which the additional lens group LC can be inserted. The state in which the additional lens group LC can be inserted is a state in which there is space for inserting the additional lens group LC, such as the telephoto end state of a zoom lens or the telephoto side focal length state of a two-focus switching lens, and the additional lens group LC is not inserted. skc is the back focus of the optical system in a state in which the additional lens group LC is inserted, and Tc is the group thickness of the additional lens group LC (the length on the optical axis from the surface closest to the object side to the surface closest to the image side). TTLm is the total optical length of the master optical system LA alone in a state in which the additional lens group LC can be inserted. Yc is the maximum image height of the optical system in a state in which the additional lens group LC is inserted. Ymm is the minimum maximum image height of the master optical system LA in all states of the master optical system LA (states in which the additional lens group LC can be inserted and states in which the additional lens group LC cannot be inserted). Additionally, θc is the total angle of view of the optical system when the additional lens group LC is inserted, and θmm is the total angle of view of the master optical system LA alone when the additional lens group LC can be inserted. Dist_c is the amount of distortion (%) at the maximum image height H when the additional lens group LC is inserted, and Dist_m is the amount of distortion (%) at the maximum image height H of the master optical system LA alone when the additional lens group LC can be inserted. fLA1 is the focal length of the first lens group L1 when the focal length of the master optical system LA is variable.

[0030] The condition of formula (2) shows an appropriate relationship between the focal length fc of the additional lens group LC and the focal length fmc of the master optical system LA alone in a state in which the additional lens group LC can be inserted, in order to achieve both the correction of distortion by the additional lens group LC and the suppression of various aberrations. If the focal length of the additional lens group LC becomes large so that fc / fmc exceeds the upper limit of formula (2), although it is possible to suppress the amount of each aberration generated in the additional lens group LC, it is not preferable because it is not possible to sufficiently correct the positive distortion, which is the original purpose. Also, if the focal length fmc of the master optical system LA becomes small so that fc / fmc exceeds the upper limit of formula (2), the refractive power of the master optical system LA becomes too strong, making it difficult to correct the positive distortion by the additional lens group LC, which is not preferable. If the focal length fc of the additional lens group LC becomes small so that fc / fmc falls below the lower limit of formula (2), the positive refractive power of the additional lens group LC becomes too strong, making it difficult to suppress curvature of field and chromatic aberration of magnification, which is undesirable. Also, if the focal length fmc of the master optical system LA becomes large so that fc / fmc falls below the lower limit of formula (2), it becomes difficult to obtain the required wide angle of view, which is undesirable.

[0031] The condition of formula (3) shows an appropriate relationship between the back focus skc of the optical system in the inserted state of the additional lens group LC and the group thickness Tc of the additional lens group LC in order to obtain a small and lightweight optical system even when the additional lens group LC is inserted. The group thickness Tc of the additional lens group LC is the length on the optical axis from the surface of the additional lens group LC closest to the object side to the surface closest to the image side. If the back focus skc becomes large so that skc / Tc exceeds the upper limit of formula (3), the total optical length of the entire optical system becomes too long, which is not preferable from the viewpoint of shortening the total length. Also, if the group thickness Tc of the additional lens group LC becomes small so that skc / Tc exceeds the upper limit of formula (3), it is preferable from the viewpoint of shortening the total length, but it is not preferable because it is necessary to reduce the number of lenses constituting the additional lens group LC, which makes it difficult to sufficiently correct distortion aberration and curvature of field. When the back focal length skc is reduced so that skc / Tc falls below the lower limit of formula (3), this is preferable from the viewpoint of shortening the overall length and correcting distortion, but the image surface becomes too close to the space into which the additional lens group LC is inserted and removed. As a result, it becomes difficult to arrange a mechanism for inserting and removing the additional lens group LC, which is not preferable. Also, when the group thickness Tc of the additional lens group LC is increased so that skc / Tc falls below the lower limit of formula (3), distortion, curvature of field, chromatic aberration of magnification, and the like are easily corrected, but the overall optical system becomes large, which is not preferable.

[0032] The condition of formula (4) shows the relationship between the total optical length TTLm of the master optical system LA alone and the group thickness Tc of the additional lens group LC in order to obtain a small and lightweight optical system even when the additional lens group LC is inserted. The total optical length TTLm of the master optical system LA is the length on the optical axis from the surface of the master optical system LA closest to the object to the image plane in a state in which the additional lens group LC can be inserted. If the total optical length TTLm of the master optical system LA becomes large so that TTLm / Tc exceeds the upper limit of formula (4), it is difficult to correct distortion with the small and lightweight additional lens group LC, which is undesirable. Also, if the group thickness Tc of the additional lens group LC becomes small so that TTLm / Tc exceeds the upper limit of formula (4), it is preferable from the viewpoint of shortening the total length of the entire optical system, but it is undesirable because it is necessary to reduce the number of lenses constituting the additional lens group LC, which makes it difficult to sufficiently correct distortion and curvature of field. If the total optical length TTLm of the master optical system LA becomes small so that TTLm / Tc falls below the lower limit of formula (4), this is advantageous for miniaturizing the entire optical system, but it is not preferable because it becomes difficult to suppress other aberrations such as field curvature while sufficiently correcting distortion with the additional lens group LC. Also, if the group thickness Tc of the additional lens group LC becomes large so that TTLm / Tc falls below the lower limit of formula (4), it becomes easier to correct distortion, field curvature, lateral chromatic aberration, etc., but it is not preferable because the entire optical system becomes large.

[0033] Equation (5) shows the appropriate relationship between the maximum image height Yc in the inserted state of the additional lens group LC and the minimum maximum image height Ymm among the maximum image heights of the master optical system LA in each state of the optical system in order to realize a wide-angle optical system in which distortion is well corrected in an image circle of an appropriate diameter. If the maximum image height Yc is increased so that Yc / Ymm exceeds the upper limit of equation (5), the difference in image circle diameter between the inserted state and the non-inserted state of the additional lens group LC becomes too large. As a result, it is necessary to increase the negative refractive power of the additional lens group LC in order to widen the image circle diameter, which is undesirable because it becomes difficult to sufficiently correct distortion.

[0034] Furthermore, when the smallest maximum image height Ymm of the master optical system LA is reduced so that Yc / Ymm exceeds the upper limit of formula (5), the difference in image circle diameter between the inserted state and the non-inserted state of the additional lens group LC becomes too large. As a result, the negative refractive power of the additional lens group LC needs to be increased in order to widen the image circle diameter, which is undesirable because it is difficult to sufficiently correct distortion. Similarly, when Yc / Ymm is below the lower limit of formula (5), the difference in image circle diameter between before and after the insertion of the additional lens group LC becomes large, so the difference in image circle diameter between the inserted state and the non-inserted state of the additional lens group LC becomes too large. As a result, the negative refractive power of the additional lens group LC needs to be increased in order to widen the image circle diameter, which is undesirable because it is difficult to sufficiently correct distortion.

[0035] The condition of formula (6) shows an appropriate relationship between the total angle of view θc of the optical system when the additional lens group LC is inserted and the total angle of view θmm of the master optical system LA alone when the additional lens group LC can be inserted, in order to perform good distortion correction with the additional lens group LC while maintaining a wide angle of view. If θc / θmm exceeds the upper limit of formula (6), the total angle of view θc in the state where the additional lens group LC is inserted becomes wider than the total angle of view θmm of the master optical system LA alone, which is not preferable because it is difficult to correct distortion with the additional lens group LC. If θc / θmm falls below the lower limit of formula (6), the angle of view in the state where the additional lens group LC is inserted becomes too small, which is not preferable because it is difficult to obtain a wide-angle optical system. In addition, the angle of view θmm of the master optical system LA alone becomes too large, which is not preferable because it is difficult to sufficiently correct distortion with the additional lens group LC.

[0036] The condition of formula (7) shows an appropriate relationship between the difference between the amount of distortion Dist_c at the maximum image height H when the additional lens group LC is inserted and the amount of distortion at the maximum image height H that occurs in the master optical system LA alone when the additional lens group LC can be inserted. If the amount of distortion Dist_c when the additional lens group LC is inserted becomes large so that Dist_c-Dist_m exceeds the upper limit of formula (7), it becomes difficult to obtain a wide-angle optical system with suppressed distortion, which is not preferable. Also, if the amount of distortion Dist_m generated in the master optical system LA becomes small so that Dist_c-Dist_m exceeds the upper limit of formula (7), the angle of view obtained by the master optical system LA becomes too narrow, which is not preferable. If the distortion amount Dist_c with the additional lens group LC inserted becomes small, such as when Dist_c-Dist_m falls below the lower limit of formula (7), this is advantageous for correcting distortion, but is undesirable because the resulting angle of view becomes more telephoto (narrower). Also, if the distortion amount Dist_m occurring in the master optical system LA becomes large, such as when Dist_c-Dist_m falls below the lower limit of formula (7), this is undesirable because it leads to an increase in the size of the master optical system LA.

[0037] The condition of formula (8) shows an appropriate relationship between the focal length fc of the additional lens group LC and the focal length of the first lens group L1 of the master optical system LA when the master optical system LA is a zoom lens. By satisfying the condition of formula (8), good distortion correction can be realized by the small and lightweight additional lens group LC. If the focal length fc of the additional lens group LC becomes small so that fc / fLA1 exceeds the upper limit of formula (8), the refractive power of the additional lens group LC becomes too large, making it difficult to sufficiently correct distortion and curvature of field, which is not preferable. Also, if the focal length fLA of the first lens group L1 becomes too large so that fc / fLA1 exceeds the upper limit of formula (8), the retrofocus arrangement in the zoom lens is weakened, which leads to an increase in the size of the entire optical system of the first lens group L1s in order to obtain the required wide angle of view, which is not preferable. If the focal length fc of the additional lens group LC becomes large, such as when fc / fLA1 falls below the lower limit of formula (8), the refractive power of the additional lens group LC becomes too small, making it impossible to sufficiently correct distortion, which is undesirable. Also, if the focal length fLA of the first lens group L1 becomes too small, such as when fc / fLA1 falls below the lower limit of formula (8), this is advantageous for making the master optical system LA wider-angle, but the refractive power of the first lens group L1 becomes too strong. As a result, it becomes difficult for the additional lens group LC to correct various aberrations occurring in the master optical system LA, which is undesirable.

[0038] It is more preferable to set the numerical ranges of the formulas (1) to (8) as follows:

[0039] 0.6≦βc≦1.2 (1a) 5≦fc / fmc≦150 (2a) 0.2≦skc / Tc≦1.1 (3a) 2.5≦TTLm / Tc≦7.0 (4a) 0.91≦Yc / Ymm≦3.00 (5a) 0.4≦θc / θmm≦1.0 (6a) 35≦Dist_c-Dist_m≦70 (7a) -8≦fc / fLA1≦-3 (8a) Moreover, it is more preferable to set the numerical ranges of the formulas (1) to (8) as follows:

[0040] 0.7≦βc≦1.2 (1b) 6.5≦fc / fmc≦105 (2b) 0.3≦skc / Tc≦1.0 (3b) 3≦TTLm / Tc≦6 (4b) 0.95≦Yc / Ymm≦2.00 (5b) 0.5≦θc / θmm≦0.8 (6b) 41≦Dist_c-Dist_m≦65 (7b) -6.8≦fc / fLA1≦-5.5 (8b) Examples 1 to 5 will be specifically described below. Example 5 is followed by Numerical Examples 1 to 5 corresponding to Examples 1 to 5, respectively. In each Numerical Example, A indicates various values ​​of the master optical system LA when the additional lens group LC is not inserted, and B indicates various values ​​of the optical system when the additional lens group LC is inserted.

[0041] In each numerical example, surface number m indicates the order of the surface when counted from the object side. r indicates the radius of curvature of the mth surface, and d (mm) indicates the distance (spacing) on ​​the optical axis between the mth surface and the (m+1)th surface. nd indicates the refractive index at the d-line of the optical material between the mth surface and the (m+1)th surface, and νd indicates the Abbe number based on the d-line of the optical material between the mth surface and the (m+1)th surface. The Abbe number based on the d-line, νd, is given by Nd, NF, and NC, respectively, when the refractive indices at the d-line (wavelength 587.6 nm), F-line (wavelength 486.1 nm), and C-line (wavelength 656.3 nm) of the Fraunhofer lines are Nd, NF, and NC, respectively. νd=(Nd-1) / (NF-NC) The effective diameter is the diameter (mm) of the area of ​​the mth surface through which light rays that contribute to image formation pass.

[0042] Each numerical example also shows the focal length (mm), F-number, and half angle of view (°) of the optical system. Note that d, focal length, F-number, and half angle of view in each numerical example are values ​​when the optical system is focused on an object at infinity. Furthermore, each numerical example shows the maximum image height corresponding to the half angle of view as "image height."

[0043] BF stands for back focus (mm). Back focus is the distance on the optical axis from the final surface of the optical system (the lens surface closest to the image) to the paraxial image surface, expressed as an air-equivalent length. "Lens total length" is the distance on the optical axis from the foreground (the lens surface closest to the object) of the optical system to the final surface plus the back focus, and is equivalent to the optical total length.

[0044] An asterisk (*) next to a surface number indicates that the surface has an aspheric shape. When X is the displacement from the apex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, and A12 are the aspheric coefficients of each order, x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 The "e±XX" in the conic constant and aspheric coefficient is expressed as "×10± XX " means.

[0045] Table 1 shows the relationship between the conditions of the above-mentioned expressions (1) to (8) and each numerical example. EXAMPLES

[0046] In the optical system of Example 1 (Numerical Example 1) shown in Figures 1(a) and (b), the master optical system LA is a zoom lens composed of a first lens group L1 with negative refractive power, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power, and a fourth lens group L4 with positive refractive power, which are arranged in this order from the object side to the image side. The third lens group L3 includes an aperture stop SP. During zooming from the wide-angle end to the telephoto end, the first lens group L1 is fixed, the second lens group L2 moves toward the image side, and the third lens group L3 and the fourth lens group L4 move toward the object side. During focusing from infinity to a close distance, the second lens group L2 moves toward the image side.

[0047] An additional lens group LC is inserted into the master optical system LA at the telephoto end, on the image side of the final surface of the master optical system LA. The additional lens group LC is composed of a positive lens, a positive lens, and a negative lens arranged in that order from the object side to the image side, and has positive refractive power as a whole. The two positive lenses in the additional lens group LC are aspheric lenses, and the positive lens on the image side has an inflection point so that the aspheric amount of the peripheral portion is negative.

[0048] The master optical system LA in Numerical Example 1 is a zoom lens having a zoom ratio of 1.88 and an angle of view in the fisheye region of about F-number 4.12. The maximum image height H of the master optical system LA at the wide-angle end is 11.15 mm, the total angle of view calculated by paraxial calculation (ftanθ system) is 107°, and the actual angle of view taking distortion into account is 174°, which is a fisheye region. The maximum image height H of the master optical system LA at the telephoto end is 21.64 mm, the total angle of view calculated by paraxial calculation is 109°, and the actual angle of view taking distortion into account is 175°, which is a fisheye region. In the master optical system LA, when the image circle on the image plane IP is set to 21.64 mm, which is the maximum image height at the telephoto end, a roughly circular fisheye image can be obtained at the wide-angle end. The optical system with the additional lens group LC inserted has a total angle of view of 127°.

[0049] Figures 2(A), (B), (C), and (D) show the longitudinal aberration (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system of Numerical Example 1. Figures 2(A), (B), and (C) respectively show the longitudinal aberration of the optical system (master optical system LA) at the wide-angle end, at the intermediate zoom position, and at the telephoto end with the additional lens group LC not inserted, and Figure 2(D) shows the longitudinal aberration of the optical system with the master optical system LA at the telephoto end and the additional lens group LC inserted.

[0050] In the spherical aberration diagram, Fno indicates the F-number, the solid line indicates the spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line indicates the spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line ΔS indicates the astigmatism on the sagittal image plane, and the dashed line ΔM indicates the astigmatism on the meridional image plane. The distortion diagram shows the distortion aberration at the d-line. The chromatic aberration diagram shows the lateral chromatic aberration at the g-line. ω is the half angle of view (°).

[0051] In the master optical system LA at the telephoto end, distortion exceeding -90% when the additional lens group LC is not inserted is corrected to -30% by inserting the additional lens group LC. Note that these distortion amounts are values ​​calculated at the same maximum image height H = 21.64 mm when the additional lens group LC is not inserted and when it is inserted. Also, distortion is calculated based on the general projection method (f tan θ system). EXAMPLES

[0052] In the optical system of Example 2 (Numerical Example 2) shown in Figures 3(a) and (b), the master optical system LA is a zoom lens composed of a first lens group L1 with negative refractive power, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power, a fourth lens group L4 with positive refractive power, and a fifth lens group L5 with positive refractive power, which are arranged in this order from the object side to the image side. The third lens group L3 includes an aperture stop SP. During zooming from the wide-angle end to the telephoto end, the first lens group L1 and the fifth lens group L5 are fixed, the second lens group L2 moves toward the image side, and the third lens group L3 and the fourth lens group L4 move toward the object side. During focusing from infinity to a close distance, the second lens group L2 moves toward the image side.

[0053] An additional lens group LC is inserted between the fourth lens group L4 and the fifth lens group L5 of the master optical system LA at the telephoto end. The additional lens group LC is composed of a positive lens, a positive lens, and a negative lens arranged in this order from the object side to the image side, and has a positive refractive power as a whole. The two positive lenses in the additional lens group LC are aspheric lenses, and the positive lens on the image side has an inflection point so that the aspheric amount of the peripheral portion is negative.

[0054] The master optical system LA in Numerical Example 2 is a zoom lens having a zoom ratio of 1.87 and an angle of view in the fisheye region of about F-number 4.12. The maximum image height H of the master optical system LA at the wide-angle end is 11.15 mm, the total angle of view calculated by paraxial calculation (ftanθ system) is 108°, and the actual angle of view taking distortion into account is 174°, which is a fisheye region. The maximum image height H of the master optical system LA at the telephoto end is 21.64 mm, the total angle of view calculated by paraxial calculation is 109°, and the actual angle of view taking distortion into account is 174°, which is a fisheye region. In the master optical system LA, when the image circle on the image plane IP is set to 21.64 mm, which is the maximum image height at the telephoto end, a roughly circular fisheye image can be obtained at the wide-angle end. The optical system with the additional lens group LC inserted has a total angle of view of 128°.

[0055] Figures 4(A), (B), (C), and (D) show the longitudinal aberration of the optical system of Numerical Example 2. Figures 4(A), (B), and (C) respectively show the longitudinal aberration of the optical system (master optical system LA) at the wide-angle end, at the intermediate zoom position, and at the telephoto end with the additional lens group LC not inserted, and Figure 4(D) shows the longitudinal aberration of the optical system with the master optical system LA at the telephoto end and the additional lens group LC inserted.

[0056] In the master optical system LA at the telephoto end, distortion exceeding −90% when the additional lens group LC is not inserted is corrected to −30% by inserting the additional lens group LC. EXAMPLES

[0057] In the optical system of Example 3 (Numerical Example 3) shown in Figures 5(a) and (b), the master optical system LA is a single focal length lens composed only of a first lens group L1 with positive refractive power. The first lens group L1 is composed of a total of 11 lenses, and an aperture stop SP is disposed between the fifth lens and the sixth lens. When focusing from infinity to a close distance, the entire master optical system LA 2 moves toward the object side.

[0058] An additional lens group LC is inserted on the image side of the final surface of the master optical system LA. The additional lens group LC is composed of a total of four elements: a positive lens, a negative lens, and a positive lens arranged in that order from the object side to the image side, and a cover glass with no refractive power, and has positive refractive power as a whole. The negative lens in the additional lens group LC and the positive lens on its image side are aspheric lenses. By inserting the additional lens group LC, the total lens length of the entire optical system is extended compared to when the additional lens group LC is not inserted.

[0059] The master optical system LA in Numerical Example 3 is a fisheye lens with a total angle of view of 102° calculated by paraxial calculation, an actual angle of view of 170° taking distortion into account, an Fno of approximately 2.5, and a maximum image height H of 23.64 mm based on the general projection method. The optical system with the additional lens group LC inserted has a total angle of view of 115°.

[0060] Figures 6(A) and (B) show the longitudinal aberration of the optical system of Numerical Example 3. Figure 6(A) shows the longitudinal aberration of the optical system (master optical system LA) when the additional lens group LC is not inserted, and Figure 6(B) shows the longitudinal aberration of the optical system when the additional lens group LC is inserted.

[0061] In the master optical system LA, distortion, which is about -88% at the maximum image height H=23.64 mm when the additional lens group LC is not inserted, is corrected to -27% by inserting the additional lens group LC. EXAMPLES

[0062] In the optical system of Example 4 (Numerical Example 4) shown in Figures 7(a) and (b), the master optical system LA is a single focal length lens composed only of a first lens group L1 with positive refractive power. The first lens group L1 is composed of a total of 11 lenses, and an aperture stop SP is disposed between the fifth lens and the sixth lens. When focusing from infinity to a close distance, the entire master optical system LA 2 moves toward the object side.

[0063] An additional lens group LC is inserted on the image side of the final surface of the master optical system LA. The additional lens group LC is composed of a positive lens, a negative lens, a positive lens, and a positive lens arranged in order from the object side to the image side, and has a positive refractive power as a whole. The negative lens in the additional lens group LC and the positive lens adjacent to it on the image side are aspheric lenses, and the positive lens among them has an inflection point so that the aspheric amount of the peripheral portion becomes negative. In this embodiment, even if the additional lens group LC is inserted, the total lens length of the entire optical system remains unchanged.

[0064] The master optical system LA in Numerical Example 4 is a fisheye lens with a total angle of view of 107° calculated by paraxial calculation, an actual angle of view of 159° taking distortion into account, an Fno of approximately 2.5, and a maximum image height H of 23.64 mm based on the general projection method. The optical system with the additional lens group LC inserted has a total angle of view of 127°.

[0065] Figures 8(A) and (B) show the longitudinal aberration of the optical system of Numerical Example 4. Figure 8(A) shows the longitudinal aberration of the optical system (master optical system LA) when the additional lens group LC is not inserted, and Figure 8(B) shows the longitudinal aberration of the optical system when the additional lens group LC is inserted.

[0066] In the master optical system LA, distortion, which is about -78% at the maximum image height H=23.64 mm when the additional lens group LC is not inserted, is corrected to -35% by inserting the additional lens group LC. EXAMPLES

[0067] In the optical system of Example 5 (Numerical Example 5) shown in Figures 9(a), (b), and (c), the master optical system LA is a two-focus switching lens composed of a first lens group L1 with negative refractive power, a second lens group L2 with negative refractive power, and a third lens group L3 with positive refractive power, which are arranged in this order from the object side to the image side. The third lens group L3 includes an aperture stop SP. The telephoto focal length state shown in Figure 9(b) is achieved by widening the gap between the first lens group L1 and the second lens group L2 from the wide-angle focal length state shown in Figure 9(a) and narrowing the gap between the second lens group L2 and the third lens group L3. In addition, when focusing from infinity to close range, the second lens group L2 moves toward the object side.

[0068] An additional lens group LC is inserted into the master optical system LA in the telephoto focal length state on the image side of the final surface of the master optical system LA. The additional lens group LC is composed of a positive lens, a positive lens, and a negative lens arranged in this order from the object side to the image side, and has positive refractive power as a whole. The two positive lenses in the additional lens group LC are aspheric lenses, and the positive lens on the image side has an inflection point so that the aspheric amount of the peripheral portion is negative.

[0069] The master optical system LA in Numerical Example 5 is a fisheye lens with a telephoto side focal length / wide-angle side focal length of 1.87 and an F-number of approximately 4.12. The maximum image height H of the master optical system LA in the wide-angle side focal length state is 11.15 mm, the total angle of view calculated by paraxial calculation (ftanθ system) is 107°, and the actual angle of view taking distortion into account is a fisheye region of 128°. The maximum image height H of the master optical system LA in the telephoto side focal length state is 21.64 mm, the total angle of view calculated by paraxial calculation is 109°, and the actual angle of view taking distortion into account is a fisheye region of 175°. The optical system with the additional lens group LC inserted has a total angle of view of 128°.

[0070] Figures 10A, 10B, and 10C show the longitudinal aberration of the optical system of Numerical Example 5. Figures 10A and 10B show the longitudinal aberration of the optical system (master optical system LA) in the wide-angle focal length state and the telephoto focal length state, respectively, when the additional lens group LC is not inserted. Figure 10D shows the longitudinal aberration of the optical system when the master optical system LA is in the telephoto focal length state and the additional lens group LC is inserted.

[0071] In the master optical system LA at the telephoto end, distortion exceeding −90% when the additional lens group LC is not inserted is corrected to −30% by inserting the additional lens group LC. [Numerical example 1-A] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 42.624 1.75 2.00100 29.1 52.25 2 20.501 7.69 36.94 3 40.788 1.00 1.72916 54.7 36.08 4 15.446 11.06 27.11 5 -41.907 1.00 1.49700 81.5 26.12 6 40.694 0.15 24.27 7 19.533 5.73 1.78880 28.4 23.68 8 370.733 (variable) 22.22 9* -32.412 0.92 1.59522 67.7 18.90 10 62.889 (variable) 17.57 11 23.219 1.56 1.88300 40.8 10.26 12 -1857.454 2.92 10.22 13 (Aperture) ∞ 2.24 10.01 14 41.624 2.55 1.49700 81.5 9.83 15 -13.961 0.50 2.00100 29.1 9.65 16 -18.770 0.12 9.72 17 -17.210 0.85 1.88300 40.8 9.69 18 43.697 1.01 10.46 19 -1450.374 3.18 1.49700 81.5 11.95 20 -15.265 (variable) 13.71 21 36.103 7.88 1.49700 81.5 18.25 22 -15.379 1.00 1.77250 49.6 19.78 23 -27.268 (variable) 21.37 Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-2.83224e-05 A 6= 4.33240e-08 A 8= 2.95679e-10 A10=-3.52607e-13 A12=-4.02694e-15 Various data Zoom ratio 1.88 Wide Angle Mid-Telephoto Focal length 8.25 12.83 15.48 F-number 4.12 4.12 4.12 Half angle of view (°) 53.50 52.57 54.42 Image height 11.15 16.77 21.64 Lens total length 105.00 105.00 105.00 BF 25.50 35.53 40.85 d8 3.87 5.36 4.35 d10 20.62 8.84 5.68 d20 1.88 2.16 1.00 d23 25.50 35.53 40.85 Entrance pupil position 18.10 17.54 17.06 Exit pupil position -24.28 -24.91 -22.36 Front principal point position 24.98 27.65 28.75 Back principal point position 17.25 22.69 25.38 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 -32.19 28.38 -1.51 -31.30 2 9 -35.81 0.92 0.19 -0.38 3 11 31.81 14.94 1.61 -11.77 4 21 42.60 8.88 3.08 -3.02 Single lens data Lens starting surface focal length 1 1 -41.09 2 3 -34.67 3 5 -41.37 4 7 25.95 5 9 -35.81 6 11 25.98 7 14 21.36 8 15 -57.43 9 17 -13.89 10 19 31.02 11 21 22.86 12 22 -47.39 [Numerical example 1-B] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 42.624 1.75 2.00100 29.1 52.25 2 20.501 7.69 36.94 3 40.788 1.00 1.72916 54.7 36.08 4 15.446 11.06 27.11 5 -41.907 1.00 1.49700 81.5 26.12 6 40.694 0.15 24.27 7 19.533 5.73 1.78880 28.4 23.68 8 370.733 (variable) 22.22 9* -32.412 0.92 1.59522 67.7 18.90 10 62.889 (variable) 17.57 11 23.219 1.56 1.88300 40.8 10.26 12 -1857.454 2.92 10.22 13 (Aperture) ∞ 2.24 10.01 14 41.624 2.55 1.49700 81.5 9.83 15 -13.961 0.50 2.00100 29.1 9.65 16 -18.770 0.12 9.72 17 -17.210 0.85 1.88300 40.8 9.69 18 43.697 1.01 10.46 19 -1450.374 3.18 1.49700 81.5 11.95 20 -15.265 (variable) 13.71 21 36.103 7.88 1.49700 81.5 18.25 22 -15.379 1.00 1.77250 49.6 19.78 23 -27.268 (variable) 21.37 24* 20.107 4.12 1.53110 55.9 20.56 25* 26.725 12.14 20.52 26* -14.915 2.70 1.53110 55.9 20.67 27* -13.029 0.15 21.58 28 -46.461 1.00 1.48749 70.2 21.86 29 ∞ (variable) 23.41 Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-2.83224e-05 A 6= 4.33240e-08 A 8= 2.95679e-10 A10=-3.52607e-13 A12=-4.02694e-15 Page 24 K = 0.00000e+00 A 4= 3.70243e-06 A 6=-3.52282e-07 A 8= 2.82652e-09 A10=-1.57541e-11 Page 25 K = 0.00000e+00 A 4=-1.41901e-05 A 6=-6.27229e-07 A 8= 2.76688e-09 A10=-1.20901e-11 Page 26 K = 0.00000e+00 A 4= 2.53486e-04 A 6=-8.40197e-07 A 8=-2.40677e-09 A10= 2.30889e-11 Page 27 K = 0.00000e+00 A 4= 2.99566e-04 A 6= 1.10387e-07 A 8=-5.08638e-09 A10= 4.26120e-11 Various data Focal length 15.41 F-number: 4.12 Half angle of view(°) 54.54 Image height 21.64 Lens total length 105.00 BF 18.25 d 8 9.04 d10 0.99 d20 1.00 d23 2.50 d29 18.25 Entrance pupil position 17.33 Exit pupil position -43.47 Front principal point position 28.90 Back principal point position 2.84 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 -32.19 28.38 -1.51 -31.30 2 9 -35.81 0.92 0.19 -0.38 3 11 31.81 14.94 1.61 -11.77 4 21 42.60 8.88 3.08 -3.02 5 24 213.20 20.11 -11.03 -28.69 Single lens data Lens starting surface focal length 1 1 -41.09 2 3 -34.67 3 5 -41.37 4 7 25.95 5 9 -35.81 6 11 25.98 7 14 21.36 8 15 -57.43 9 17 -13.89 10 19 31.02 11 21 22.86 12 22 -47.39 13 24 125.74 14 26 129.60 15 28 -95.31 [Numerical example 2-A] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 39.091 1.75 2.00100 29.1 51.74 2 20.380 8.02 37.05 3 41.174 1.00 1.72916 54.7 36.08 4 14.553 10.84 26.18 5 -44.370 1.00 1.49700 81.5 25.32 6 34.781 0.15 23.31 7 18.559 5.49 1.78880 28.4 22.75 8 275.732 (variable) 21.33 9* -32.166 0.92 1.59522 67.7 18.92 10 62.671 (variable) 17.57 11 22.884 1.31 1.88300 40.8 10.13 12 -363.088 3.12 10.10 13 (Aperture) ∞ 2.01 9.81 14 43.799 2.30 1.49700 81.5 9.60 15 -13.894 0.50 2.00100 29.1 9.43 16 -20.192 0.11 9.50 17 -18.477 0.85 1.88300 40.8 9.48 18 38.406 0.93 10.01 19 811.027 2.92 1.49700 81.5 11.43 20 -15.849 (variable) 13.13 21 37.828 6.91 1.49700 81.5 17.56 22 -15.419 1.00 1.77250 49.6 19.00 23 -25.792 (variable) 20.49 24 98.036 1.72 1.51633 64.1 36.56 25 265.426 (variable) 36.71 Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-2.75165e-05 A 6= 9.09105e-08 A 8=-5.80219e-10 A10=7.06254e-12 A12=-2.73442e-14 Various data Zoom ratio 1.87 Wide Angle Mid-Telephoto Focal length 8.17 12.55 15.31 F-number 4.12 4.12 4.12 Half angle of view (°) 53.76 53.20 54.71 Image height 11.15 16.77 21.64 Lens total length 104.40 104.40 104.40 BF 16.37 16.37 16.37 d 8 3.31 4.70 3.70 d10 20.02 8.93 5.82 d20 3.72 2.79 0.98 d23 8.15 18.79 24.71 d25 16.37 16.37 16.37 Entrance pupil position 18.29 17.76 17.28 Exit pupil position -39.53 -50.49 -53.18 Front principal point position 25.27 27.95 29.23 Back principal point position 8.19 3.82 1.05 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 -30.66 28.24 -0.36 -29.45 2 9 -35.58 0.92 0.19 -0.38 3 11 32.10 14.04 0.37 -11.88 4 21 40.73 7.91 3.02 -2.39 5 24 300.02 1.72 -0.66 -1.79 Single lens data Lens starting surface focal length 1 1 -44.62 2 3 -31.36 3 5 -39.07 4 7 24.99 5 9 -35.58 6 11 24.42 7 14 21.51 8 15 -46.34 9 17 -14.03 10 19 31.31 11 21 23.03 12 22 -51.81 13 24 300.02 [Numerical example 2-B] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 39.091 1.75 2.00100 29.1 51.74 2 20.380 8.02 37.05 3 41.174 1.00 1.72916 54.7 36.08 4 14.553 10.84 26.18 5 -44.370 1.00 1.49700 81.5 25.32 6 34.781 0.15 23.31 7 18.559 5.49 1.78880 28.4 22.75 8 275.732 (variable) 21.33 9* -32.166 0.92 1.59522 67.7 18.92 10 62.671 (variable) 17.57 11 22.884 1.31 1.88300 40.8 10.13 12 -363.088 3.12 10.10 13 (Aperture) ∞ 2.01 9.81 14 43.799 2.30 1.49700 81.5 9.60 15 -13.894 0.50 2.00100 29.1 9.43 16 -20.192 0.11 9.50 17 -18.477 0.85 1.88300 40.8 9.48 18 38.406 0.93 10.01 19 811.027 2.92 1.49700 81.5 11.43 20 -15.849 (variable) 13.13 21 37.828 6.91 1.49700 81.5 17.56 22 -15.419 1.00 1.77250 49.6 19.00 23 -25.792 (variable) 20.49 24* 19.839 4.10 1.53110 55.9 20.79 25* 26.908 12.06 20.73 26* -14.336 2.70 1.53110 55.9 21.09 27* -13.039 0.15 22.03 28 -55.674 1.00 1.48749 70.2 22.40 29 ∞ (variable) 23.95 30 98.036 1.72 1.51633 64.1 36.56 31 265.426 (variable) 36.71 Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-2.75165e-05 A 6= 9.09105e-08 A 8=-5.80219e-10 A10=7.06254e-12 A12=-2.73442e-14 Page 24 K = 0.00000e+00 A 4= 8.74730e-06 A 6=-3.77856e-07 A 8= 2.94420e-09 A10=-1.43021e-11 Page 25 K = 0.00000e+00 A 4=-4.80057e-06 A 6=-7.42707e-07 A 8= 3.88100e-09 A10=-1.36524e-11 Page 26 K = 0.00000e+00 A 4= 2.97670e-04 A 6=-1.44158e-06 A 8= 1.67172e-09 A10 = 1.80958e-11 Page 27 K = 0.00000e+00 A 4= 3.24500e-04 A 6=-3.22073e-07 A 8=-2.56153e-09 A10= 3.81913e-11 Various data Focal length 15.13 F-number: 4.12 Half angle of view (°) 55.03 Image height 21.64 Lens length 104.40 BF 16.37 d 8 8.53 d10 0.99 d20 0.98 d23 3.70 d29 1.00 d31 16.37 Entrance pupil position 17.57 Exit pupil position -52.66 Front principal point position 29.39 Back principal point position 1.24 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 -30.66 28.24 -0.36 -29.45 2 9 -35.58 0.92 0.19 -0.38 3 11 32.10 14.04 0.37 -11.88 4 21 40.73 7.91 3.02 -2.39 5 24 181.09 20.01 -7.34 -25.38 6 30 300.02 1.72 -0.66 -1.79 Single lens data Lens starting surface focal length 1 1 -44.62 2 3 -31.36 3 5 -39.07 4 7 24.99 5 9 -35.58 6 11 24.42 7 14 21.51 8 15 -46.34 9 17 -14.03 10 19 31.31 11 21 23.03 12 22 -51.81 13 24 118.38 14 26 157.62 15 28 -114.21 16 30 300.02 [Numerical example 3-A] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 59.149 2.00 1.77250 49.6 37.48 2 11.536 8.91 21.78 3 -85.209 1.00 1.49700 81.5 21.14 4 17.306 0.10 18.45 5 14.603 6.46 1.72000 42.0 18.24 6 -49.618 0.55 16.12 7 -30.570 0.80 1.53775 74.7 15.52 8 35.075 4.35 1.86459 39.5 13.45 9 -43.211 1.00 11.11 10 (Aperture) ∞ 1.00 10.94 11 -46.235 7.27 1.49700 81.5 10.85 12 -8.980 1.00 1.73703 26.3 13.70 13 606.079 1.20 18.88 14 -45.023 2.71 2.00100 29.1 19.27 15 -21.817 0.15 20.88 16 70.127 6.35 1.49700 81.5 29.47 17 -43.095 0.14 30.99 18 62.325 11.05 1.43875 94.7 35.55 19 -31.756 0.10 36.42 20* -100.550 2.30 1.53110 55.9 36.02 21 -153.698 (variable) 37.03 Image plane ∞ Aspheric Data Page 20 K = 0.00000e+00 A 4=-9.82365e-06 A 6= 7.32755e-09 A 8=-3.48285e-11 Various data Focal length 16.11 F-number 2.50 Half angle of view (°) 53.33 Image height 21.64 Lens length 81.19 BF 22.76 d21 22.76 Entrance pupil position 10.84 Exit pupil position -51.60 Front principal point position 23.46 Back principal point position 6.65 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 16.11 58.44 23.46 6.65 Single lens data Lens starting surface focal length 1 1 -18.90 2 3 -28.85 3 5 16.36 4 7 -30.25 5 8 22.98 6 11 21.06 7 12 -12.00 8 14 39.95 9 16 54.73 10 18 49.73 11 20 -555.85 [Numerical example 3-B] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 59.149 2.00 1.77250 49.6 37.48 2 11.536 8.91 21.78 3 -85.209 1.00 1.49700 81.5 21.14 4 17.306 0.10 18.45 5 14.603 6.46 1.72000 42.0 18.24 6 -49.618 0.55 16.12 7 -30.570 0.80 1.53775 74.7 15.52 8 35.075 4.35 1.86459 39.5 13.45 9 -43.211 1.00 11.11 10 (Aperture) ∞ 1.00 10.94 11 -46.235 7.27 1.49700 81.5 10.85 12 -8.980 1.00 1.73703 26.3 13.70 13 606.079 1.20 18.88 14 -45.023 2.71 2.00100 29.1 19.27 15 -21.817 0.15 20.88 16 70.127 6.35 1.49700 81.5 29.47 17 -43.095 0.14 30.99 18 62.325 11.05 1.43875 94.7 35.55 19 -31.756 0.10 36.42 20* -100.550 2.30 1.53110 55.9 36.02 21 -153.698 (variable) 37.03 22 -42.303 1.39 1.95907 17.5 27.83 23 -38.045 0.15 28.26 24* -49.190 1.50 1.53110 55.9 28.42 25* 61.938 6.22 28.68 26* -356.070 3.23 1.53110 55.9 29.62 27 -32.489 0.20 31.11 28 ∞ 1.50 1.51633 64.1 34.47 29 ∞ (variable) 35.23 Image plane ∞ Aspheric Data Page 20 K = 0.00000e+00 A 4=-9.82365e-06 A 6= 7.32755e-09 A 8=-3.48285e-11 Page 24 K = 0.00000e+00 A 4= 3.99956e-05 A 6=-4.64956e-08 Page 25 K = 0.00000e+00 A 4= 1.60773e-05 A 6= 2.95560e-08 Page 26 K = 0.00000e+00 A 4=-4.12891e-05 A 6=-3.52081e-08 A 8= 1.19774e-10 Various data Focal length 18.69 F-number 2.90 Half angle of view(°) 49.17 Image height 21.64 Lens length 88.32 BF 9.91 d21 5.79 d29 9.91 Entrance pupil position 10.84 Exit pupil position -95.64 Front principal point position 26.22 Back principal point position -8.79 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 16.11 58.44 23.46 6.65 2 22 1678.59 14.19 249.02 279.18 Single lens data Lens starting surface focal length 1 1 -18.90 2 3 -28.85 3 5 16.36 4 7 -30.25 5 8 22.98 6 11 21.06 7 12 -12.00 8 14 39.95 9 16 54.73 10 18 49.73 11 20 -555.85 12 22 339.71 13 24 -51.38 14 26 67.08 15 28 0.00 [Numerical Example 4-A] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 58.358 2.00 1.77250 49.6 38.28 2 11.564 9.80 22.20 3 -52.069 1.00 1.49700 81.5 21.93 4 16.849 0.10 19.75 5 15.588 7.22 1.72000 42.0 19.78 6 -40.710 1.26 18.20 7 -20.372 0.80 1.53775 74.7 17.62 8 18.175 5.48 1.51705 52.5 15.64 9 -20.055 1.00 14.64 10 (Aperture) ∞ 1.00 14.15 11 -51.045 10.13 1.49700 81.5 14.16 12 -11.236 1.00 2.00089 27.1 17.52 13 -37.770 0.19 22.01 14 -35.215 2.39 2.00100 29.1 22.11 15 -22.864 0.15 23.36 16 193.580 5.72 1.49700 81.5 28.87 17 -33.882 0.15 30.12 18 -196.151 7.13 1.43875 94.7 32.10 19 -26.513 0.15 33.09 20* -117.453 2.30 1.53110 55.9 33.34 21 -86.493 (variable) 34.04 Image plane ∞ Aspheric Data Page 20 K = 0.00000e+00 A 4=-6.72551e-06 A 6=-3.71087e-09 A 8=-1.89959e-11 Various data Focal length 17.67 F-number 2.50 Half angle of view (°) 50.76 Image height 21.64 Lens total length 100.05 BF 41.09 d21 41.09 Entrance pupil position 11.55 Exit pupil position -45.95 Front principal point position 25.63 Back principal point position 23.42 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 17.67 58.96 25.63 23.42 Single lens data Lens starting surface focal length 1 1 -19.02 2 3 -25.49 3 5 16.54 4 7 -17.73 5 8 19.39 6 11 26.73 7 12 -16.29 8 14 59.38 9 16 58.51 10 18 68.99 11 20 602.31 [Numerical example 4-B] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 58.358 2.00 1.77250 49.6 38.28 2 11.564 9.80 22.20 3 -52.069 1.00 1.49700 81.5 21.93 4 16.849 0.10 19.75 5 15.588 7.22 1.72000 42.0 19.78 6 -40.710 1.26 18.20 7 -20.372 0.80 1.53775 74.7 17.62 8 18.175 5.48 1.51705 52.5 15.64 9 -20.055 1.00 14.64 10 (Aperture) ∞ 1.00 14.15 11 -51.045 10.13 1.49700 81.5 14.16 12 -11.236 1.00 2.00089 27.1 17.52 13 -37.770 0.19 22.01 14 -35.215 2.39 2.00100 29.1 22.11 15 -22.864 0.15 23.36 16 193.580 5.72 1.49700 81.5 28.87 17 -33.882 0.15 30.12 18 -196.151 7.13 1.43875 94.7 32.10 19 -26.513 0.15 33.09 20* -117.453 2.30 1.53110 55.9 33.34 21 -86.493 (variable) 34.04 22 96.962 1.50 1.77250 49.6 27.95 23 364.816 16.22 27.94 24* -23.564 1.50 1.53110 55.9 28.67 25* 107.115 5.35 28.11 26* 57.730 3.22 1.53110 55.9 28.79 27 -37.730 0.20 30.66 28 155.905 1.50 1.48749 70.2 35.03 29 ∞ (variable) 35.31 Image plane ∞ Aspheric Data Page 20 K = 0.00000e+00 A 4=-6.72551e-06 A 6=-3.71087e-09 A 8=-1.89959e-11 Page 24 K = 0.00000e+00 A 4= 1.00171e-04 A 6=-5.57130e-08 Page 25 K = 0.00000e+00 A 4= 5.81386e-06 A 6= 1.53929e-07 Page 26 K = 0.00000e+00 A 4=-8.64674e-05 A 6=-5.65693e-08 A 8= 2.09465e-10 Various data Focal length 16.71 F-number: 2.36 Half angle of view (°) 52.32 Image height 21.64 Lens length 100.06 BF 9.61 d21 2.00 d29 9.61 Entrance pupil position 11.55 Exit pupil position -229.62 Front principal point position 27.09 Back principal point position -7.10 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 17.67 58.96 25.63 23.42 2 22 121.97 29.49 32.06 2.96 Single lens data Lens starting surface focal length 1 1 -19.02 2 3 -25.49 3 5 16.54 4 7 -17.73 5 8 19.39 6 11 26.73 7 12 -16.29 8 14 59.38 9 16 58.51 10 18 68.99 11 20 602.31 12 22 170.54 13 24 -36.22 14 26 43.47 15 28 319.81 [Numerical Example 5-A] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 41.285 1.75 2.00100 29.1 53.78 2 20.770 8.80 38.03 3 45.288 1.00 1.72916 54.7 36.99 4 15.470 11.10 27.32 5 -42.815 1.00 1.49700 81.5 26.52 6 48.163 0.15 24.82 7 19.305 5.68 1.78880 28.4 24.08 8 171.521 (variable) 22.59 9* -35.764 0.92 1.59522 67.7 19.36 10 61.767 (variable) 18.01 11 23.637 2.83 1.88300 40.8 10.25 12 -659.757 2.28 10.17 13(Aperture) ∞ 2.00 9.98 14 46.191 2.64 1.49700 81.5 9.79 15 -13.071 0.50 2.00100 29.1 9.61 16 -16.664 0.14 9.68 17 -15.855 0.85 1.88300 40.8 9.63 18 48.327 1.84 9.80 19 505.293 3.09 1.49700 81.5 12.44 20 -15.117 1.00 13.88 21 38.465 6.78 1.49700 81.5 17.84 22 -15.692 1.00 1.77250 49.6 18.99 23 -31.370 (variable) 20.48 Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-3.38388e-05 A 6= 1.56590e-07 A 8=-1.51270e-09 A10= 1.29546e-11 A12=-4.03897e-14 Various data Focal length 8.19 15.33 F-number 4.12 4.12 Half angle of view (°) 53.71 54.68 Image height 11.15 21.64 Lens length 106.57 106.80 BF 25.94 40.81 d 8 4.02 4.84 d10 21.26 5.80 d23 25.94 40.81 Entrance pupil position 18.88 17.86 Exit pupil position -21.99 -21.99 Front principal point position 25.67 29.45 Back principal point position 17.75 25.48 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 -31.65 29.48 -0.63 -31.19 2 9 -37.92 0.92 0.21 -0.36 3 11 23.41 24.95 10.24 -14.24 Single lens data Lens starting surface focal length 1 1 -43.62 2 3 -32.69 3 5 -45.44 4 7 27.13 5 9 -37.92 6 11 25.89 7 14 20.81 8 15 -65.09 9 17 -13.44 10 19 29.59 11 21 23.40 12 22 -41.81 [Numerical example 5-B] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 41.285 1.75 2.00100 29.1 53.78 2 20.770 8.80 38.03 3 45.288 1.00 1.72916 54.7 36.99 4 15.470 11.10 27.32 5 -42.815 1.00 1.49700 81.5 26.52 6 48.163 0.15 24.82 7 19.305 5.68 1.78880 28.4 24.08 8 171.521 (variable) 22.59 9* -35.764 0.92 1.59522 67.7 19.36 10 61.767 (variable) 18.01 11 23.637 2.83 1.88300 40.8 10.25 12 -659.757 2.28 10.17 13(Aperture) ∞ 2.00 9.98 14 46.191 2.64 1.49700 81.5 9.79 15 -13.071 0.50 2.00100 29.1 9.61 16 -16.664 0.14 9.68 17 -15.855 0.85 1.88300 40.8 9.63 18 48.327 1.84 9.80 19 505.293 3.09 1.49700 81.5 12.44 20 -15.117 1.00 13.88 21 38.465 6.78 1.49700 81.5 17.84 22 -15.692 1.00 1.77250 49.6 18.99 23 -31.370 (variable) 20.48 24* 19.927 3.77 1.53110 55.9 20.55 25* 26.226 11.83 20.36 26* -13.995 2.70 1.53110 55.9 20.73 27* -13.028 0.15 21.53 28 -64.799 1.00 1.48749 70.2 21.86 29 ∞ (variable) 23.15 Image plane ∞ Aspheric Data 9th page K = 0.00000e+00 A 4=-3.38388e-05 A 6= 1.56590e-07 A 8=-1.51270e-09 A10= 1.29546e-11 A12=-4.03897e-14 Page 24 K = 0.00000e+00 A 4= 1.74076e-05 A 6=-5.22832e-07 A 8= 4.60273e-09 A10=-1.92514e-11 Page 25 K = 0.00000e+00 A 4= 6.90955e-06 A 6=-9.38721e-07 A 8= 6.35325e-09 A10=-2.24639e-11 Page 26 K = 0.00000e+00 A 4= 3.15884e-04 A 6=-1.12667e-06 A 8=-1.03106e-09 A10 = 2.41102e-11 Page 27 K = 0.00000e+00 A 4= 3.31976e-04 A 6= 1.52246e-07 A 8=-6.34407e-09 A10= 4.60401e-11 Various data Focal length 15.15 F-number: 4.12 Half angle of view (°) 54.99 Image height 21.64 Lens length 106.80 BF 18.87 d 8 9.63 d10 1.00 d23 2.49 d29 18.87 Entrance pupil position 18.13 Exit pupil position -44.61 Front principal point position 29.66 Back principal point position 3.72 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 -31.65 29.48 -0.63 -31.19 2 9 -37.92 0.92 0.21 -0.36 3 11 23.41 24.95 10.24 -14.24 4 24 192.25 19.45 -5.05 -23.00 Single lens data Lens starting surface focal length 1 1 -43.62 2 3 -32.69 3 5 -45.44 4 7 27.13 5 9 -37.92 6 11 25.89 7 14 20.81 8 15 -65.09 9 17 -13.44 10 19 29.59 11 21 23.40 12 22 -41.81 13 24 129.35 14 26 180.27 15 28 -132.92

[0072] [Table 1]

[0073] [Imaging device] Fig. 12 shows a digital still camera (imaging device) using the optical system of Examples 1 to 5 as an imaging lens. In Fig. 12, 10 is a camera body, and 11 is an imaging lens configured with any of the optical systems of Examples 1 to 5. 12 is an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that is built into the camera body 10 and receives (captures) an optical image formed by the imaging lens 11. The camera body 10 may be a single-lens reflex camera having a quick-turn mirror, or may be a mirrorless camera without a quick-turn mirror.

[0074] In this way, by using the optical system of each embodiment in an imaging device, it is possible to obtain a small-sized imaging device capable of generating images with a wide angle of view and good quality.

[0075] The above embodiment includes the following configurations.

[0076] (Configuration 1) An optical system having a first optical system and a second optical system that can be inserted and removed from a surface of the first optical system closest to the object toward an image side, the second optical system is configured such that, when inserted into the optical system, distortion at a maximum image height is reduced by 10% or more compared to when not inserted, When the lateral magnification of the second optical system is βc, 0.5≦βc≦1.3 An optical system characterized by satisfying the following conditions. (Configuration 2) Let fc be the focal length of the second optical system, and fmc be the focal length of the first optical system alone in a state in which the second optical system can be inserted. 4≦fc / fmc≦200 2. The optical system according to claim 1, wherein the following condition is satisfied: (Configuration 3) When the back focus of the optical system in the inserted state of the second optical system is skc, and the length on the optical axis from the surface of the second optical system closest to the object side to the surface closest to the image side is Tc, 0.1≦skc / Tc≦1.2 3. The optical system according to configuration 1 or 2, which satisfies the following condition: (Configuration 4) When the total optical length of the first optical system in a state in which the second optical system can be inserted is TTLm, 2≦TTLm / Tc≦10 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) Let Yc be the maximum image height of the optical system when the second optical system is inserted, and Ymm be the minimum of the maximum image heights of the first optical system when the second optical system can be inserted and when the second optical system cannot be inserted, 0.9≦Yc / Ymm≦3.0 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) When the total angle of view of the optical system in a state in which the second optical system is inserted is θc, and the total angle of view of the first optical system alone in a state in which the second optical system can be inserted is θmm, 0.3≦θc / θmm≦1.2 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) When the amount of distortion at the maximum image height of the optical system in a state where the second optical system is inserted is Dist_c (%), and the amount of distortion at the maximum image height generated by the first optical system alone in a state where the second optical system can be inserted is Dist_m (%), 15≦Dist_c-Dist_m≦80 7. The optical system according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) the first optical system has a focal length that can be changed by changing an interval between a plurality of lens groups; Let fc be the focal length of the second optical system, and fLA1 be the focal length of the first lens group that is the lens group closest to the object side, -12≦fc / fLA1≦-1 8. The optical system according to any one of configurations 1 to 7, wherein the following condition is satisfied: (Configuration 9) The optical system according to any one of configurations 1 to 8, wherein the second optical system includes one or more negative lenses and one or more positive lenses and has a positive refractive power overall. (Configuration 10) the second optical system includes an aspheric lens, 10. The optical system according to any one of configurations 1 to 9, wherein a peripheral portion within an effective diameter of the aspherical lens has a negative aspherical amount. (Configuration 11) 11. The optical system according to configuration 10, wherein the aspherical lens has an inflection point where the aspherical amount changes between positive and negative. (Configuration 12) 12. The optical system according to any one of configurations 1 to 11, wherein the second optical system is inserted on the image side of an aperture stop included in the first optical system. (Configuration 13) 13. The optical system according to any one of configurations 1 to 12, wherein the second optical system is inserted on the image side of the surface of the first optical system that is closest to the image side. (Configuration 14) 14. The optical system according to any one of configurations 1 to 13, wherein the total optical length of the optical system is unchanged whether the second optical system is inserted or not. (Configuration 15) An optical system according to any one of configurations 1 to 14; and an image sensor for capturing an optical image formed by the optical system. (Configuration 16) a second optical system that can be inserted and removed from a surface of the first optical system closest to the object toward an image side, the second optical system is configured such that, when inserted into the first optical system, distortion at a maximum image height is reduced by 10% or more compared to when not inserted; When the lateral magnification of the second optical system is βc, 0.5≦βc≦1.3 The second optical system satisfies the following conditions:

[0077] The embodiments described above are merely representative examples, and various modifications and alterations are possible for each embodiment when implementing the present invention. [Explanation of symbols]

[0078] LA Master optical system (first optical system) LC Additional lens group (second optical system) IP image plane SP aperture stop

Claims

1. An optical system having a first optical system and a second optical system that can be inserted and removed from a surface of the first optical system closest to the object toward an image side, the second optical system is configured such that, when inserted into the optical system, distortion at a maximum image height is reduced by 10% or more compared to when not inserted, When the lateral magnification of the second optical system is βc, 0.5≦βc≦1.3 An optical system characterized by satisfying the following conditions.

2. When the focal length of the second optical system is fc, and the focal length of the first optical system alone in a state in which the second optical system can be inserted is fmc, 4≦fc / fmc≦200 2. The optical system according to claim 1, which satisfies the following condition:

3. When the back focus of the optical system in the inserted state of the second optical system is skc, and the length on the optical axis from the surface of the second optical system closest to the object side to the surface closest to the image side is Tc, 0.1≦skc / Tc≦1.2 2. The optical system according to claim 1, which satisfies the following condition:

4. When the total optical length of the first optical system in a state in which the second optical system can be inserted is TTLm, 2≦TTLm / Tc≦10 2. The optical system according to claim 1, which satisfies the following condition:

5. Let Yc be the maximum image height of the optical system when the second optical system is inserted, and Y mm be the minimum of the maximum image heights of the first optical system when the second optical system can be inserted and when the second optical system cannot be inserted, 0.9≦Yc / Ymm≦3.0 2. The optical system according to claim 1, which satisfies the following condition:

6. When the total angle of view of the optical system in a state in which the second optical system is inserted is θc, and the total angle of view of the first optical system alone in a state in which the second optical system can be inserted is θmm, 0.3≦θc / θmm≦1.2 2. The optical system according to claim 1, which satisfies the following condition:

7. When the amount of distortion aberration at the maximum image height of the optical system in a state in which the second optical system is inserted is Dist_c (%), and the amount of distortion aberration at the maximum image height generated by the first optical system alone in a state in which the second optical system can be inserted is Dist_m (%), 15≦Dist_c−Dist_m≦80 2. The optical system according to claim 1, which satisfies the following condition:

8. the first optical system has a variable focal length by changing an interval between a plurality of lens groups; When the focal length of the second optical system is fc and the focal length of the first lens group, which is the lens group closest to the object side, is fLA1, −12≦fc / fLA1≦−1 2. The optical system according to claim 1, which satisfies the following condition:

9. The optical system according to claim 1 , wherein the second optical system includes one or more negative lenses and one or more positive lenses, and has a positive refractive power as a whole.

10. the second optical system includes an aspheric lens, 2. The optical system according to claim 1, wherein a peripheral portion within an effective diameter of the aspherical lens has a negative aspherical amount.

11. The optical system according to claim 10 , wherein the aspheric lens has an inflection point at which the refractive power changes from positive to negative.

12. The optical system according to claim 1 , wherein the second optical system is inserted on the image side of an aperture stop included in the first optical system.

13. The optical system according to claim 1 , wherein the second optical system is inserted on the image side of a surface of the first optical system that is closest to the image side.

14. 2. The optical system according to claim 1, wherein the total optical length of said optical system is unchanged whether said second optical system is inserted or not.

15. An optical system according to any one of claims 1 to 14; and an image sensor for capturing an optical image formed by the optical system.

16. a second optical system that can be inserted and removed from a surface of the first optical system closest to the object toward an image side, the second optical system is configured such that, when inserted into the first optical system, distortion at a maximum image height is reduced by 10% or more compared to when not inserted; When the lateral magnification of the second optical system is βc, 0.5≦βc≦1.3 The second optical system satisfies the following conditions:

Images