WO2019244866A1

WO2019244866A1 - Lens system and imaging device

Info

Publication number: WO2019244866A1
Application number: PCT/JP2019/024030
Authority: WO
Inventors: 悠哉宮下
Original assignee: 株式会社ｎｉｔｔｏｈ
Priority date: 2018-06-19
Filing date: 2019-06-18
Publication date: 2019-12-26
Also published as: JP2021152559A

Abstract

This imaging lens system (10) is configured from a negative refractive power first lens group (G1), a positive refractive power second lens group (G2), a positive refractive power third lens group (G3) and a positive refractive power fourth lens group (G4), arranged in order from the object side (11). When focusing from infinity to very close, the distance (d6) along the optical axis (15) between the first lens group (G1) and the second lens group (G2) increases, the distance (d9) between the second lens group (G2) and the third lens group (G3) decreases, and the fourth lens group (G4) is fixed relative to the image plane (5) as well as to an aperture (St) arranged on the object side (11) of the fourth lens group.

Description

Lens system and imaging device

The present invention relates to a lens system and an imaging device having the same.

Japanese Patent Application Laid-Open No. 2012-53260 discloses a bright macro lens with little aberration variation from an infinity object in-focus state to a close-distance object in-focus state in which the magnification is the same as that of an object at positive magnification. A first lens unit, a negative second lens unit, a positive third lens unit, and a negative fourth lens unit. A macro lens is disclosed in which during focusing, the first unit and the fourth unit do not move, the second unit moves to the image side, and the third unit moves to the object side together with the stop.

レンズ There is a need for a lens system that is easier to handle and that can obtain an image in which aberrations have been well corrected, and an imaging device including the same.

One embodiment of the present invention is a lens system for imaging, which includes a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a positive lens unit arranged in order from the object side. And a fourth lens group having a positive refractive power, and a first lens group along the optical axis and a second lens group along the optical axis when focusing from infinity to the nearest. The distance between the second lens group and the third lens group is reduced, and the distance between the second lens group and the third lens group is reduced. The fourth lens group is located on the object side of the fourth lens group together with the stop. Fixed lens system.

In this lens system, when focusing from infinity to the closest distance, the distance between the first lens group in the negative group and the second lens group in the positive group is increased, so that the front side (object side) is focused. The position can be moved to a short distance. On the other hand, by increasing the distance between the first lens group and the second lens group and decreasing the distance between the second lens group and the fourth lens group, the distance between the first lens group and the second lens group is reduced. The combined power of the second lens unit and the fourth lens unit becomes stronger than the combined power of the above, and the principal point position is shifted to the image plane side. For this reason, the focal length of the entire system of the lens system fluctuates to the short focal length side, and the ray height of the axial ray among the rays incident on the second lens group of the positive lens group increases. However, by moving the third lens group of the positive group toward the object side so as to approach the second lens group, it is possible to correct the fluctuation of the focal length of the entire system due to the movement of the second lens group. While the positive power of the entire lens system is moved to the front side and the principal point position is returned to the original position, the light beam having a higher ray height is bent so as to be converged by the third lens group and is incident on the fourth lens group. Can be done.

Therefore, even if the stop provided on the object side of the fourth lens group is fixed together with the fourth lens group, it is possible to prevent light from being kicked by the stop. Therefore, it is possible to fix the aperture during focusing, and it is possible to suppress a change in the F value due to focusing. In addition, since the lens group that moves during focusing can be centrally arranged on the object side of the aperture, it is possible to prevent the aperture from being caught in the lens movement mechanism, and with a simple structure, good focus from the nearest point to infinity A lens system with high performance can be provided.

The focal length f2 of the second lens group and the focal length f3 of the third lens group may satisfy the following condition.
1.0 ≦ f2 / f3 ≦ 1.5
During focusing from infinity to the nearest, the first lens group is fixed with respect to the image plane, the second lens group moves toward the image plane, and the third lens group moves toward the object side. Is also good.

The movement amount FL1 of the second lens group and the movement amount FL2 of the third lens group may satisfy the following conditions.
2.5 ≦ FL1 / FL2 ≦ 4.5

The second lens group may include a first cemented lens, and the third lens group may include a second cemented lens. The third lens group may include at least one object-side convex meniscus lens having a positive refractive power and disposed on the object side of the second cemented lens. The first cemented lens may be a meniscus lens convex on the image side, and the second cemented lens may be a meniscus lens convex on the object side.

Furthermore, the fourth lens group may include a third cemented lens arranged on the object side and a fourth cemented lens arranged on the image plane side. The effective diameter B1D of the first cemented lens, the effective diameter B2D of the second cemented lens, the effective diameter B3D of the third cemented lens, and the effective diameter B4D of the fourth cemented lens satisfy the following conditions. Is also good.
B1D> B2D
B3D <B4D

The difference between the Abbe number B1p of the lens having the positive refractive power of the first cemented lens and the Abbe number B1m of the lens having the negative refractive power, and the Abbe number B2p of the lens having the positive refractive power of the second cemented lens are negative. The difference between the Abbe number B2m of the lens having a positive refractive power, the difference between the Abbe number B3p of the lens having a positive refractive power of the third cemented lens, and the Abbe number B3m of the lens having a negative refractive power, and the fourth joint The difference between the Abbe number B4p of the lens having a positive refractive power and the Abbe number B4m of the lens having a negative refractive power may satisfy the following condition.
| B1p-B1m | <| B2p-B2m |
| B3p-B3m |> | B4p-B4m |

The focal length f1 of the first lens group and the focal length f2 of the second lens group may satisfy the following condition.
1.0 ≦ | f2 / f1 | ≦ 1.15

The first lens group may include a first lens having a positive refractive power meniscus convex to the object side closest to the object side. The first lens group includes a second lens having a negative refractive power disposed adjacent to the positive meniscus lens. The first lens group has a thickness Ld1 on the optical axis of the first lens, the first lens and the second lens. The distance Ld12 on the optical axis from the lens may satisfy the following condition.
0.35 ≦ Ld12 / Ld1 ≦ 0.70

Another aspect of the present invention is an imaging apparatus including the above-described lens system and an imaging element arranged on an image plane side of the lens system.

FIG. 1 is a diagram illustrating a schematic configuration of a lens system and an imaging device of the present example. The figure which shows lens data. The figure which shows the numerical value which fluctuates at the time of focusing. The figure which shows an aspherical surface coefficient. FIG. 4 is a diagram showing various aberrations when the focal length is at infinity. FIG. 4 is a diagram illustrating various aberrations when a focal length is standard (intermediate distance). FIG. 4 is a diagram illustrating various aberrations when the focal length is closest. The figure which shows the schematic structure of another example of a lens system and an imaging device. FIG. 9 is a diagram showing lens data of the lens system in FIG. 8. The figure which shows the numerical value which fluctuates at the time of focusing. The figure which shows an aspherical surface coefficient. FIG. 4 is a diagram showing various aberrations when the focal length is at infinity. FIG. 4 is a diagram illustrating various aberrations when a focal length is standard (intermediate distance). FIG. 4 is a diagram illustrating various aberrations when the focal length is closest.

Embodiment of the Invention

FIG. 1 shows an example of an imaging device (camera, camera device) provided with an optical system for imaging. FIG. 1A shows an arrangement of each lens having a focus at infinity, and FIG. 1B shows an arrangement of each lens having a closest focus. The camera 1 includes an optical system (imaging optical system, imaging optical system, lens system) 10 and an imaging device (imaging system) arranged on the image plane side (image side, imaging side, imaging side) 12 of the optical system 10. Device, image plane) 5. The optical system 10 is a lens system 10 for imaging, and is a lens system having four groups and 16 elements. Specifically, the lens system 10 includes a first lens group G1 having a negative refractive power, which is arranged in order from the object side 11 and has a fixed position with respect to the image plane 5, and an optical axis 15 during focusing. The second lens group G2 and the third lens group G3 having a positive refractive power and moving along the second lens group G3 and the third lens group G3 are fixed in position with respect to the image plane 5, and a stop (aperture stop) St is disposed on the object side 11; A fourth lens group G4 having a positive refractive power, and an image is formed on the image plane 5 by the four lens groups G1 to G4.

レンズ The high-performance lens system 10 with high aberration correction capability generally has a large number of lenses and a large aperture. For this reason, it is heavy and difficult to handle, and it is not easy to obtain a stable image. In particular, a lens system for photographing a high-quality image such as a movie has a large number of lenses, which is close to 10 to 20, and is difficult to handle in a handy manner. Further, since the F-number fluctuates due to the movement of the aperture during focusing, it is a task that requires the skill and experience of the photographer to obtain an image with little fluctuation in brightness while focusing. . On the other hand, the lens system 10 of the present invention is a lens system in which the aperture St does not move during focusing (focusing), and the fluctuation of the F value is small.

The first lens group G1 having the negative refractive power disposed closest to the object side 11 of the lens system 10 includes a meniscus lens L11 having a positive refractive power convex toward the object side 11 and disposed in order from the object side 11. , A meniscus lens L12 having a negative refractive power convex on the object side 11 and a biconcave negative lens L13. That is, the first lens group G1 is a lens group having a positive-negative-negative power arrangement arranged in order from the object side 11. The second lens group G2 having a positive refracting power has a two-element configuration including a biconcave negative lens L21 and a biconvex positive lens L22 from the object side 11, and the entire image is formed by the negative lens L21 and the positive lens L22. A first cemented lens B1 having a positive refractive power and convex on the surface side 12 is formed. That is, the second lens group G2 has a negative-positive power arrangement arranged in order from the object side 11, and these are lens groups that constitute a cemented lens.

The third lens group G3 having a positive refractive power as a whole includes a meniscus lens L31 having a positive refractive power convex on the object side 11 and a positive refractive power convex on the object side 11, which are arranged in order from the object side 11. , A meniscus lens L33 having a positive refractive power convex on the object side 11, and a meniscus lens L34 having a negative refractive power concave on the image plane side 12. The positive meniscus lens L33 and the negative meniscus lens L34 constitute a second cemented lens B2 having a negative refractive power that is convex on the object side 11 (concave on the image plane side 12) as a whole. That is, the third lens group G3 has a positive-positive-positive-negative power arrangement arranged in order from the object side 11, and the positive-negative lens on the image plane side 12 (the side facing the stop St). Is a lens group composed of a cemented lens by

A fourth lens group G4 having a positive refractive power and disposed closest to the image plane 12 includes a biconcave negative lens L41, a biconvex positive lens L42 and an image plane A meniscus lens L43 having a positive refractive power convex on the side 12, a biconcave negative lens L44, a biconvex positive lens L45, a negative meniscus lens L46 convex on the image plane side 12, and a biconvex positive lens This is a seven-sheet configuration with L47. The negative lens L41 and the positive lens L42 constitute a third cemented lens B3 having a negative refractive power that is concave on the object side 11 (convex on the image plane side 12) as a whole. The biconcave negative lens L44 and the biconvex positive lens L45 form a fourth cemented lens B4 having a concave refractive power on the object side 11 (convex on the image plane side 12) and a negative refractive power as a whole. . In other words, the fourth lens group G4 has a negative-positive-positive-negative-positive-negative-positive power arrangement arranged in order from the object side 11, and the fourth lens group G4 has the object side 11 (the side facing the stop St). This is a lens group in which a cemented lens is constituted by a negative-positive lens, and a cemented lens is constituted by a negative-positive lens sandwiched between lenses having a positive power.

A stop St is disposed on the object side 11 of the fourth lens group G4. The stop St is such that the second cemented lens B2 is disposed on the object side 11 without interposing any other lens, and the stop St is on the image side 12 The third cemented lens B3 is arranged without interposing another lens.

FIG. 2 shows data of each lens constituting the lens system 10 shown in FIG. A surface Si (i is a number, the same applies hereinafter) indicates a surface of each lens arranged in order from the object side 11, and a curvature ri indicates a radius of curvature (mm) of each surface of each lens arranged in order from the object side 11. , The distance di indicates the distance (mm) between the lens surfaces, the refractive index ni indicates the refractive index (d line) of each lens, the Abbe number νi indicates the Abbe number (d line) of each lens, and The diameter Di indicates an effective diameter (mm) of each surface of each lens. The same applies to the following embodiments.

FIG. 3 shows the combined focal length of the lens system 10 at infinity, standard (object distance 2280 mm), and closest (object distance 630 mm) focusing positions (focus positions) of the lens system 10 shown in FIG. F value (Fno), angle of view (degree), distance d6 between first lens group G1 and second lens group G2, distance d9 between second lens group G2 and third lens group G3, And a distance d16 between the third lens group G3 and the fourth lens group G4 (specifically, a distance to the stop St).

レンズ The lens system of the present invention will be further described based on the lens system 10 shown in FIG. The lens system 10 is an imaging lens system, and includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, arranged in order from the object side 11, and A lens system suitable for a middle-telephoto lens of a retrofocus type having a total of four groups, including a third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power. It is. During focusing from infinity to the closest distance, the lens system 10 increases the distance d6 between the first lens group G1 and the second lens group G2 along the optical axis 15 and increases the distance between the second lens group G2 and the third lens group G2. The distance d9 between the third lens group G3 and the fourth lens group G4 decreases (d16 + d17 if the stop St is not included). That is, at the time of focusing, the second lens group G2 and the third lens group G3 move independently along the optical axis 15, and the fourth lens group G4 moves toward the object side of the fourth lens group G4. 11 does not move together with the stop St, and is fixed to the image plane 5.

More specifically, in this lens system 10, during focusing from infinity to the closest distance, the first lens group G1 is fixed with respect to the image plane 5, and the second lens group G2 is fixed with respect to the image plane. 12, the third lens group G3 moves to the object side 11. Therefore, during focusing, the first lens group G1 closest to the object side 11 and the fourth lens group G4 closest to the image plane 12 do not move during focusing, and the total length of the lens system 10 is constant. , An inner focus type lens system in which a second lens group G2 and a third lens group G3 move.

In this lens system 10, the distance between the first lens group G1 in the negative group and the second lens group G2 in the positive group is increased at the time of focusing from infinity to the closest distance, so that ) The focus position of 11 can be moved to a short distance. On the other hand, the distance between the first lens group G1 and the second lens group G2 is increased, and the distance between the second lens group G2 and the fourth lens group G4 is reduced. Compared with the power combined with the second lens group G2, the combined power of the second lens group G2 and the fourth lens group G4 becomes stronger, and the principal point position shifts to the image plane side 12. As a result, the focal length of the entire system of the lens system 10 fluctuates to the short focal length side, and among the rays incident on the second lens group G2 in the positive group, the ray height of the on-axis ray (light from the on-axis marginal ray) (The height up to the axis 15 in the direction orthogonal to the optical axis 15). However, by moving the third lens group G3 of the positive group toward the object side 11 so as to approach the second lens group G2, the fluctuation of the focal length of the entire system due to the movement of the second lens group G2 is corrected. The positive power of the entire lens system 10 is moved to the front side to return the principal point position to the original position, and the light beam having a higher light height is bent so as to be converged by the third lens group G3. 4 lens group G4.

上 Note that the on-axis ray here is a ray that is emitted from a light spot disposed on the optical axis and passes through the stop St, and the principal ray of the on-axis ray is the on-axis principal ray. Further, a marginal ray of an on-axis ray (on-axis marginal ray) is a ray that is the most distant from the on-axis principal ray among rays emitted from light spots arranged on the optical axis (the end of the entrance pupil of the optical system). ), And is defined as a light beam that defines a light beam width that is the width of a light beam of an on-axis light beam.

Therefore, even if the stop St is fixed together with the fourth lens group G4, it is possible to prevent light from being kicked by the stop St. Therefore, by fixing the aperture St during focusing, fluctuations in the F value can be suppressed. Further, since the lens group that moves during focusing can be concentratedly arranged on the object side 11 of the stop St, it is possible to prevent the stop St from being caught in the lens moving mechanism, and with a simple structure, from the closest point to infinity. It is possible to provide the lens system 10 that can obtain good focus performance. Further, it is possible to provide the lens system 10 in which the fluctuation of the F value due to the focusing is small and the image having the small fluctuation of the brightness can be easily obtained.

In addition, the entire length of the lens system 10 does not change during focusing, and the lens groups that move during focusing can be limited to the adjacent second lens group G2 and third lens group G3. The mechanism can be simplified. Further, since the moving directions of the second lens group G2 and the third lens group G3 that move during focusing are reversed, the change in the center of gravity of the lens system 10 as a whole is small. Therefore, it is possible to provide the lens system 10 that is easy to handle and can be used in a handy type.

In the lens system 10, the focal length f2 of the second lens group G2 and the focal length f3 of the third lens group G3 may satisfy the following condition (1).
1.0 ≦ f2 / f3 ≦ 1.5 (1)
In order to compensate for the influence of the movement of the second lens group G2 by the movement of the third lens group G3, it is desirable that the refractive powers of the respective lens groups G2 and G3 are substantially equal. For this reason, when the value goes below the lower limit of the condition (1), the refractive power of the third lens group G3 becomes too small, so that it is difficult to satisfactorily correct spherical aberration and axial chromatic aberration. When the value exceeds the upper limit of the condition (1), the refractive power of the second lens group G2 becomes too small, and it becomes difficult to satisfactorily correct spherical aberration.

The movement amount FL1 of the second lens group G2 and the movement amount FL2 of the third lens group G3 may satisfy the following condition (2).
2.5 ≦ FL1 / FL2 ≦ 4.5 (2)
The second lens group G2 needs to secure a movement amount FL1 for obtaining focusing performance from infinity to the closest distance. That is, the lens system 10 moves the principal point position by a retrofocus configuration by increasing the distance between the first lens group G1 in the negative group and the second lens group G2 in the positive group, thereby changing the focal length. Is shortened and the image forming position on the object side 11 is brought closer to the image plane side (camera side) 12. In addition, in order to suppress the fluctuation of the focal length at this time, the third lens group G3 of the positive group disposed on the image plane side 12 of the second lens group G2 is brought closer to the object side 11 so that the lens system 10 The positive power in the vicinity of the center is increased to reduce the height of the on-axis light beam spread by the first lens unit G1 in the negative lens unit, and at the same time, the positive power on the rear side of the optical system (image side rather than the stop). The position of the principal point is restored by weakening.

Therefore, in condition (2), if the value goes below the lower limit, the movement amount FL2 of the third lens group G3 becomes too large, so that the movement amount FL1 of the second lens group G2 cannot be relatively secured, and the second lens group The group G2 cannot be separated from the first lens group G1, which makes it difficult to sufficiently adjust the imaging position and correct each aberration. For this reason, it becomes difficult to correct spherical aberration, curvature of field, and chromatic aberration of magnification. On the other hand, when the value exceeds the upper limit of the condition (2), the moving amount FL1 of the second lens group G2 is too large, so that the moving amount FL2 of the third lens group G3 becomes too small, and the second lens group G3 becomes too small. The correction of the movement of the focal length due to the movement of the group G2 cannot be completely corrected, the field angle greatly changes, and the correction of the curvature of field becomes difficult.

In the lens system 10, the second lens group G2 includes a first cemented lens B1, the third lens group G3 includes a second cemented lens B2, and the fourth lens group G4 includes a third cemented lens. Includes a lens B3 and a fourth cemented lens B4. The cemented lens B1 of the second lens group G2 and the second cemented lens B2 of the third lens group G3 move independently during focusing. For this reason, the fluctuation of the axial chromatic aberration and the chromatic aberration of magnification due to focusing can be shared and corrected by the respective cemented lenses B1 and B2. In particular, the cemented lens B1 into which a ray having a high ray height of the off-axis ray (the height in a direction orthogonal to the optical axis 15 from the off-axis marginal ray most distant from the optical axis 15 to the optical axis 15) is incident, the chromatic aberration of magnification is reduced. The cemented lens B2 having a high correction capability and a low-off-axis light beam incident thereon has a high correction capability for axial chromatic aberration.

The term “off-axis light beam” used herein refers to the main light beam that is incident on the lens surface closest to the object side 11 among the main light beams that are emitted from a light spot disposed off the optical axis and pass through the stop St. This is a light ray having the largest angle with the axis 15. The principal ray of the off-axis ray is defined as an off-axis principal ray. A marginal ray of an off-axis ray (off-axis marginal ray) is a ray that is the most distant from the off-axis principal ray among the off-axis rays, and is a ray that defines a ray width that is the width of the luminous flux of the off-axis ray. . Incidentally, the off-axis marginal ray has a different distance from the optical axis 15 depending on the position on the light beam cross section orthogonal to the off-axis principal ray. Therefore, of the off-axis marginal rays incident on the lens surface closest to the object side 11, the ray whose distance to the optical axis 15 is the largest (the distance from the optical axis 15) is defined as the lower marginal ray. The light ray with the shortest distance (closest) is defined as an upper marginal light ray.

Furthermore, the third lens group G3 includes at least one meniscus lens having a positive refractive power convex on the object side 11 disposed on the object side 11 of the second cemented lens B2. In this example, the third lens group G3 includes two positive meniscus lenses L31 and L32 that are convex on the object side 11 on the object side 11 of the cemented lens B2.

The positive meniscus lenses L31 and L32 bend the axial marginal ray so as to strongly converge on the axial principal ray side, and act in a direction to reduce the ray height of the axial ray. Therefore, it is possible to reduce the size of the second cemented lens B2 disposed on the image plane side 12 of the positive meniscus lenses L31 and L32, and the aperture St subsequent thereto. On the other hand, the positive meniscus lenses L31 and L32 generate aberrations related to axial rays. However, the positive meniscus lenses L31 and L32 are arranged with the convex surface facing the object side 11 to suppress the occurrence of spherical aberration and to reduce the curvature of the surface of each lens because it is divided into two pieces. Can be. For this reason, the generation of aberrations including spherical aberration by the positive meniscus lenses L31 and L32 is suppressed. As for the off-axis rays, the rays incident on the peripheral side of the convex surface of the positive meniscus lenses L31 and L32 on the object side 11 are bent toward the optical axis 15 side, but are bent to the opposite side by the concave surface on the image side 12. . For this reason, as a result, it is possible to converge the incident angle and the outgoing angle of the off-axis principal ray and the off-axis marginal ray without breaking. Therefore, it is possible to suppress the aberration caused by the imbalance.

In the third lens group G3, the positive meniscus lenses L31 and L32 that are convex on the object side 11 are arranged to effectively reduce the height of axial rays, and are arranged on the image plane side 12 thereof. The lens diameter of the cemented lens B2 can be reduced. The positive meniscus lenses L31 and L32 converge the beam width (the distance from the upper marginal ray to the lower marginal ray in a cross section orthogonal to the off-axis principal ray) due to the upper marginal ray and the lower marginal ray of the off-axis ray. By generating coma aberration on the opposite side to the coma aberration generated by the cemented lens B2 having negative power disposed on the image plane side 12, coma aberration can be suppressed as a whole. The number of the positive meniscus lens disposed on the object side 11 of the third lens group G3 may be one, but by dividing the positive meniscus lens into two lenses, the power is distributed to the lenses L31 and L32, and It is possible to weaken the power of the lens and to loosen the radius of curvature, thereby further suppressing the occurrence of each aberration.

The first cemented lens B1 may be a meniscus lens convex on the image side 12, and the second cemented lens B2 may be a meniscus lens convex on the object side 11. By arranging a meniscus lens-type cemented lens B2 convex on the object side 11 (concave on the image plane side 12) on the object side 11 of the stop St, the stop St can be miniaturized. In addition, by disposing a meniscus-type cemented lens B1 facing the opposite direction on the object side 11 of the cemented lens B2, spherical aberration generated by these cemented lenses B1 and B2 can be effectively corrected. In addition, the cemented lens B1 is a combination of negative and positive from the object side 11, and the cemented lens B2 is a combination of positive and negative from the object side 11, and the power arrangement is also an object in addition to the surface shape. Spherical aberration can be suppressed more effectively.

Further, as described above, in the lens system 10, the fourth lens group G4 includes the third cemented lens B3 arranged on the object side 11 and the fourth cemented lens B4 arranged on the image plane side 12. including. Accordingly, in the lens system 10, the first cemented lens B1 and the second cemented lens B2, and the third cemented lens B3 and the fourth cemented lens B4 are symmetrically arranged with the stop St interposed therebetween. And aberration can be independently shared and corrected in each optical system divided by the stop St. Therefore, the lens system 10 has a high chromatic aberration correction capability as a whole.

Further, the effective diameter B1D of the first cemented lens B1, the effective diameter B2D of the second cemented lens B2, the effective diameter B3D of the third cemented lens B3, and the effective diameter B4D of the fourth cemented lens B4 The following condition (3) may be satisfied.
B1D> B2D
B3D <B4D (3)
The effective diameter Di of the surface closest to the object side 11 can be adopted as a typical effective diameter of each cemented lens. In the present lens system 10, the following condition (3a) can be satisfied.
D7> D14
D18 <D23 (3a)

Further, the difference between the Abbe number B1p (ν8) of the lens L22 having the positive refractive power of the first cemented lens B1 and the Abbe number B1m (ν7) of the lens L21 having the negative refractive power, and the difference of the second cemented lens B2 The difference between the Abbe number B2p (ν14) of the lens L33 having a positive refractive power and the Abbe number B2m (ν15) of the lens L34 having a negative refractive power, and the Abbe number of the lens having a positive refractive power L42 of the third cemented lens B3. The difference between the number B3p (ν19) and the Abbe number B3m (ν18) of the lens L41 having a negative refractive power, and the Abbe number B4p (ν24) of the lens L45 having a positive refractive power of the fourth cemented lens B4 and the negative refraction. The difference between the force and the Abbe number B4m (ν23) of the lens L45 may satisfy the following condition (4).
| B1p-B1m | <| B2p-B2m |
| B3p-B3m |> | B4p-B4m | ... (4)

レンズ This lens system 10 includes a total of four cemented lenses B1 to B4. When the condition (3) or (3a) is satisfied, these four cemented lenses B1 to B4 are arranged in the order of “high-low-low-high” when viewing the ray height of the off-axis ray from the object side 11. When the condition (4) is satisfied, the difference between the Abbe numbers of the positive lens and the negative lens forming the four cemented lenses B1 to B4 is arranged in the order of "small-large-large-small". For this reason, as a whole of the lens system 10, the two cemented lenses B1 and B2 and B3 and B4 can be arranged symmetrically with respect to the difference between the ray height and the Abbe number across the stop St. . Therefore, the lens system 10 has a high chromatic aberration correction ability.

In the lens system 10, before and after the stop St, the third lens group G3 is the cemented lens B2 disposed closest to the image side 12 and the object side 11 of the stop St, and Includes a cemented lens B2 including a concave surface on the object side 11. The fourth lens group G4 is a cemented lens B3 disposed on the image plane side 12 of the stop St, which is closest to the object side 11, and the surface S18 on the object side 11 has a concave surface on the image plane side 12. Including the cemented lens B3. By arranging the cemented lenses B2 and B3 before and after the stop St at which the height of off-axis rays becomes low, axial chromatic aberration can be mainly corrected. In addition, when the concave surfaces of the cemented lenses B2 and B3 face each other, coma aberration and distortion in the opposite directions are generated, thereby canceling each other, and aberration correction can be performed efficiently.

Further, the cemented lens B2 is a combination of a lens L33 having a positive power and a lens L34 having a negative power from the object side 11, and the cemented lens B3 is a lens L41 having a negative power and a lens L42 having a positive power from the object side 11. It is a combination of Therefore, the cemented lenses B2 and B3 allow the lenses to be arranged symmetrically with respect to the positive / negative-negative / positive direction with the stop St interposed therebetween, thereby effectively correcting axial aberrations such as spherical aberration, axial chromatic aberration, and coma. it can. Specifically, the lens L34 having the concave surface S16 on the object side 11 of the stop St is a negative meniscus lens having a negative power convex on the object side 11 and a positive meniscus lens having a positive power on the object side 11 having a positive power. And the cemented lens B2. A lens L41 having a concave surface S18 on the image plane side 12 of the stop St is a biconcave negative lens, and forms a cemented lens B3 with a biconvex positive lens L42.

Further, the radius of curvature g3er (r16) of the concave surface S16 on the object side 11 facing the stop St of the cemented lenses B2 and B3 and the radius of curvature g4fr (r18) of the concave surface S18 on the image side 12 are as follows. Condition (5) may be satisfied.
2.5 ≦ | g4fr / g3er | ≦ 4.0 (5)
By forming a symmetric arrangement with the stop St as a center by the cemented lenses B2 and B3 arranged on both sides of the stop St, aberration correction can be favorably performed as described above. On the other hand, by adding an asymmetric configuration in which the radius of curvature r18 of the concave surface S18 on the image surface side 12 is made smaller than the radius of curvature r16 of the concave surface S16 on the object side 11 of the aperture St, the retro-focus type aperture St It is possible to relax the sensitivity of the fourth lens group G4, which has a higher tolerance sensitivity after the above. Therefore, it is possible to provide a lens system in which aberration is satisfactorily corrected, performance is stable, and handling is easy.

Further, the angle of incidence of off-axis rays on the surface S18 on the image plane side 12 of the stop St can be reduced. For this reason, an effect that the occurrence of underframes (inward frames) can be suppressed can be obtained. Therefore, when the value goes below the lower limit of the condition (5), it becomes difficult to correct spherical aberration and curvature of field. When the value exceeds the upper limit of the condition (5), it becomes difficult to correct spherical aberration and axial chromatic aberration.

The second cemented lens B2 arranged on the object side 11 of the stop St of the lens system 10 and the third cemented lens B3 arranged on the image plane side 12 of the stop St have a negative refractive power, and The focal length B2f of the cemented lens B2 and the focal length B3f of the third cemented lens B3 may satisfy the following condition (6).
1.7 ≦ B3f / B2f ≦ 3.0 (6)
In the retro-farcus type lens system 10 preceded by the first lens group G1 having a negative power, the cemented lenses B2 and B3 are disposed symmetrically before and after the stop St to improve the aberration correction performance and improve the object side. By making the power of the cemented lens B2 of the lens unit 11 stronger than that of the cemented lens B3 of the image plane side 12, the light beam is more strongly focused on the object side 11 of the stop St, and the image plane side 12 including the stop St is stopped. Can be made compact. When the value exceeds the upper limit of the condition (6), the power of the cemented lens B3 with respect to the cemented lens B2 becomes too weak, so that it is difficult to cancel spherical aberration generated in the cemented lens B2, and the balance with the cemented lens B2 is lost. It becomes difficult to sufficiently correct axial chromatic aberration. Conversely, when the value goes below the lower limit of the condition (6), the power of the cemented lens B3 with respect to the cemented lens B2 becomes too strong, so that the balance with the cemented lens B2 is lost and it becomes difficult to correct axial chromatic aberration. Since the ability to diverge the off-axis ray becomes stronger, the emission angles of the upper and lower marginal rays of the off-axis ray with respect to the principal ray of the off-axis ray emitted from the cemented lens B3 diverge. For this reason, the balance between the off-axis principal ray and the off-axis marginal ray of the off-axis ray is lost, and it becomes difficult to correct lateral chromatic aberration. Therefore, when the value goes below the lower limit of the condition (6), it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration. When the value goes above the upper limit of the condition (6), correction of spherical aberration and axial chromatic aberration becomes difficult.

The fourth lens group G4 further includes a meniscus lens L43 having a positive refractive power concave on the object side 11 disposed on the image plane side 12 of the cemented lens B3 disposed on the image plane side 12 of the stop St. By arranging a concave positive meniscus lens L43 on the object side 11 close to the image side 12 of the fourth lens G4 convex on the image side 12, the beam width of the off-axis ray can be reduced. By adjusting the balance between the width of the upper marginal light beam and the width of the lower marginal light beam, it is possible to correct each aberration generated in the off-axis light beam.

Further, the radius of curvature B3er (r20) of the surface S20 convex on the image surface side 12 of the cemented lens B3 and the concave radius on the object side 11 of the object side 11 of the meniscus lens L43 having a positive refractive power. The curvature radius Lbfr (r21) of the surface S21 may satisfy the following condition (7).
1.35 ≦ | B3er / Lbfr | ≦ 1.55 (7)
The curvature r20 (B3er) of the convex surface S20 on the image surface side 12 of the cemented lens B3 is made larger (loose) than the curvature r21 (Lbfr) of the concave surface S21 on the object side 11 of the positive meniscus lens L43. The emitted off-axis light rays converge in the direction of reducing the light beam width, and the convergent off-axis light rays can be made almost parallel by the concave surface S21. At this time, the off-axis ray emitted from the convex surface S20 is refracted as a whole away from the optical axis, but the ray is more strongly bent from the upper marginal ray to the lower marginal ray. As a result, off-axis rays converge as a result. That is, when the off-axis light beam that crosses the optical axis 15 enters the concave surface S21, all the light beams enter the curved surface on one side of the optical axis 15 of the concave surface S21. Therefore, the closer the light ray is to the optical axis 15, the greater the angle of incidence on the convex surface S20 is, and the more the light beam is bent. Thereby, it is possible to adjust the balance between the width of the off-axis ray and the width of the upper marginal ray with respect to the principal ray and the width of the lower marginal ray with respect to the principal ray, and it is possible to correct each aberration generated in the off-axis ray. Become.

When the value exceeds the upper limit of the condition (7), the power of the concave surface S21 increases, and the off-axis marginal ray of the off-axis ray incident on the concave face S21 with respect to the off-axis principal ray diverges. And the correction of spherical aberration and chromatic aberration of magnification becomes difficult. Conversely, when the value goes below the lower limit of the condition (7), the power of the concave surface S21 becomes weak, and the convergent off-axis light beam incident on the concave surface S21 cannot be returned to almost parallel. And the correction of spherical aberration and axial chromatic aberration becomes difficult.

The fourth lens group G4 includes a cemented lens (fourth cemented lens) B4 disposed on the image plane side 12 of the meniscus lens L43 having a positive refractive power. The radius of curvature Lber (r22) of the surface S22 convex on the image surface side 12 of the image surface side 12 of the positive meniscus lens L43 and the curvature of the object surface 11 of the fourth cemented lens B4 and the concave surface S23 on the object side 11 of the fourth cemented lens B4. The radius of curvature B4fr (r23) may satisfy the following condition (8).
1.03 ≦ | Lber / B4fr | ≦ 1.07 (8)

An air lens (air lens portion) is formed between the positive meniscus lens L43 and the fourth cemented lens B4 adjacent to the image plane side 12, and the surface S22 of the meniscus lens L43 on the image plane side 12 and the fourth cemented lens. By bringing the surface s23 of the object side 11 of B4 close to and satisfying the condition (8), the distance of the peripheral portion can be made substantially zero. In this air lens, the upper and lower marginal rays of the off-axis rays emitted from the convex surface S22 on the image plane side 12 of the positive meniscus lens L43 are bent so as to converge to the off-axis principal ray side. At this time, the lens thickness of the air lens increases from the upper marginal ray to the lower marginal ray. For this reason, the lower marginal ray converges to the off-axis principal ray side more than the upper marginal ray, and the off-axis principal ray enters substantially perpendicularly and does not bend. As a result, in the air lens, the beam width is reduced such that the lower marginal beam mainly converges.

(4) Thereafter, a slightly convergent off-axis ray is incident on the concave surface S23 on the object side 11 of the fourth cemented lens B4. At this time, the off-axis chief ray is incident substantially perpendicularly and does not bend, but the upper and lower marginal rays diverge in a direction away from the off-axis chief ray. Furthermore, the upper marginal ray is bent in a direction that is more divergent than the lower marginal ray. As a result, the presence of the air lens converges so that the width between the lower marginal ray and the off-axis principal ray is preferentially narrower than the width between the upper marginal ray and the principal ray. For this reason, it becomes possible to further adjust the balance of off-axis rays, and to correct each aberration favorably.

If the upper limit of the condition (8) is exceeded, the curvature of the concave surface S23 becomes too small (stiff) as compared with the convex surface S22, so that the light rays emitted from the air lens portion are excessively diverged. For this reason, the balance between the off-axis marginal ray and the off-axis chief ray is lost, and it becomes difficult to correct spherical aberration and curvature of field. When the value goes below the lower limit of the condition (8), on the contrary, the curvature of the convex surface S22 approaches the absolute value of the curvature of the concave surface S23. For this reason, the divergence of the light beam emitted from the air lens becomes too weak, the balance between the off-axis marginal light beam and the off-axis chief ray is lost, and it becomes difficult to correct spherical aberration and axial chromatic aberration.

The object S on the image side 12 of the third cemented lens B3 disposed on the image side 12 of the stop St, the surface S20 convex on the image side 12, and the object 11 on the object side 11 of the meniscus lens L43 having a positive refractive power. The distance Ld41 (d20) on the optical axis 15 from the concave surface S21 on the side 11 and the surface S22 convex on the image surface side 12 of the image surface side 12 of the meniscus lens L43 having a positive refractive power, and positive refraction The distance Ld43 (d22) on the optical axis 15 between the object side 11 of the fourth cemented lens B4 disposed on the image side 12 of the force meniscus lens L43 and the concave surface S23 on the object side 11 is as follows. Condition (9) may be satisfied.
7 ≦ Ld41 / Ld43 ≦ 23 (9)

When the value goes below the lower limit of the condition (9), the air lens between the positive meniscus lens L43 and the fourth cemented lens B4 becomes too thick, and it becomes difficult to correct spherical aberration and curvature of field. Exceeding the upper limit of condition (9) is difficult because it exceeds the limit at which the lens interval can be mechanically adjusted.

In addition, the surface S20 of the third cemented lens B3 disposed on the image plane side 12 of the stop St, the surface S20 convex to the image plane side 12, and the object side 11 of the meniscus lens L43 having a positive refractive power. The distance Ld41 (d20) on the optical axis 15 from the concave surface S21 on the object side 11 on the optical axis 15 and the thickness Ld42 (d21) on the optical axis 15 of the meniscus lens L43 having a positive refractive power satisfy the following condition (10). ) May be satisfied.
0.6 ≦ Ld41 / Ld42 ≦ 1.0 (10)
When the value exceeds the upper limit of the condition (10), the distance Ld41 (d20) between the third cemented lens B3 and the positive meniscus lens L43 becomes larger than the thickness Ld42 (d21) of the positive meniscus lens L43. For this reason, of the rays incident on the interval Ld41, the off-axis chief ray and the off-axis marginal ray are excessively converged, and in particular, the convergence direction of the off-axis chief ray and the lower marginal ray as compared with the upper marginal ray. The way of turning is strong. As a result, the width between the off-axis chief ray and the off-axis marginal ray is excessively converged while being out of balance, so that spherical aberration and lateral chromatic aberration are excessively corrected. Conversely, when the value goes below the lower limit of the condition (10), the distance Ld41 (d20) becomes too thin as compared with the thickness Ld42 (d21), so that the off-axis ray enters the positive meniscus lens L43 without being sufficiently converged. For this reason, it becomes difficult to correct spherical aberration and lateral chromatic aberration.

As described above, by configuring the second lens group G2, the third lens group G3, and the fourth lens group G4 having a positive power, it is possible to provide the lens system 10 in which the aberration is satisfactorily corrected. Further, the lens system 10 is a retrofocus type in which negative power precedes, and the focal length f1 of the first lens group G1 and the focal length f2 of the second lens group G2 satisfy the following condition (11). May be satisfied.
1.0 ≦ | f2 / f1 | ≦ 1.15 (11)
In condition (11), when the value exceeds the upper limit, the focal length f2 of the second lens group G2 as the positive group is too large with respect to the focal length f1 of the first lens group G1 as the negative group. The power of the second lens group G2 is insufficient for the lens group G1. For this reason, even if the distance between the second lens group G2 and the first lens group G1 is changed by moving the second lens group G2, the power arrangement when the respective groups are combined within the lens system 10 is sufficiently increased. It cannot be changed, making it difficult to adjust the focus position. Further, since the power of the second lens group G2 of the positive group becomes weaker than that of the first lens group G1 of the negative group, the balance between the negative power and the positive power is lost, and it is difficult to correct axial chromatic aberration. Become.

Conversely, when the value goes below the lower limit of the condition (11), the focal length of the positive second lens unit G2 is too small with respect to the negative first lens unit G1, and the power of the first lens unit G1 is too small. The power of the second lens group G2 is too strong. This is advantageous in that the amount of movement of the second lens group G2 of the positive group during focusing is reduced, but the power of the positive second lens group G2 becomes too strong and the negative first lens group G2 becomes too strong. The positive power balance with respect to G1 is lost, and the axial chromatic aberration is excessively corrected, making correction difficult. Further, the balance between the on-axis principal ray and the on-axis marginal ray emitted from the positive second lens group G2 and the balance between the off-axis principal ray and the off-axis marginal ray of the off-axis ray are lost, and the focus is lost. The fluctuation of aberration before and after becomes large.

The first lens group G1 may include the first lens L11 having a positive refractive power and a meniscus convex to the object side 11 closest to the object side 11. By arranging the convex lens L11 on the most object side 11 where the ray height becomes large, it becomes possible to effectively correct aberrations such as distortion generated by the negative power configuration arranged on the image plane side 12. . Further, by forming the convex lens L11 as a meniscus lens having a convex surface facing the object side 11 in particular, it is possible to effectively reduce the ray height without increasing the power while suppressing the spherical aberration generated in the convex lens L11. For this reason, it is possible to suppress an increase in the rear lens diameter while suppressing the occurrence of chromatic aberration and the like.

Further, the first lens group G1 includes a second lens L12 having a negative refractive power disposed adjacent to the positive meniscus lens L11, and has a thickness Ld1 (d1) on the optical axis of the first lens L11. The distance Ld12 (d2) on the optical axis 15 between the first lens L11 and the second lens L12 may satisfy the following condition (12).
0.35 ≦ Ld12 / Ld1 ≦ 0.70 (12)
In the condition (12), when the value exceeds the upper limit, the distance Ld12 (d2) between the lenses becomes too large, so that the off-axis rays and the on-axis rays emitted from the positive meniscus lens L11 converge too much and the ray height becomes too small. I will. For this reason, the correction capability of the positive meniscus lens L11 for the aberration caused by the negative lens group including the second lens L12 disposed on the image plane side 12 of the positive meniscus lens L11 of the first lens group G1 becomes excessive, Spherical aberration and field curvature are strongly generated.

Conversely, when the value goes below the lower limit of the condition (12), the distance Ld12 (d2) between the lenses becomes too small, so that off-axis rays and on-axis rays emitted from the positive meniscus lens L11 cannot be converged and the ray height is high. A light ray enters the negative meniscus lens L12 on the image plane side 12 of the first lens group G1. For this reason, the divergence ability of the negative meniscus lens L12 acts strongly, and the ability of the positive meniscus lens L11 to correct aberration generated by the negative lens group of the first lens group G1 is insufficient. Therefore, it is difficult to correct spherical aberration and axial chromatic aberration.

As shown in FIG. 3, the lens system 10 shown in FIG. 1 is a middle-telephoto lens having a focus range from infinity to a closest distance of 630 mm and a focal length at infinity of 95 mm. The lens system 10 has a total of 16 lenses, and has a total length (distance from the lens surface closest to the object side 11 to the lens surface closest to the image plane side) LA of 169.72 mm and a distance to the imaging surface 5 of 219.96 mm. This is a relatively compact lens system, and is an inner focus type lens system in which the second lens group G2 and the third lens group G3 move during focusing. The F-number at each focal length is a constant and small value of 1.68, and the lens system does not move and the F-number does not fluctuate during focusing (focusing).

As shown in FIG. 4, the surface 27 of the fourth lens group G4 on the image plane side 12 of the negative meniscus lens L46 that is convex on the image plane side 12 is aspheric. Assuming that X is the coordinates in the optical axis direction, Y is the coordinates in the direction perpendicular to the optical axis, the traveling direction of light is positive, and R is the paraxial radius of curvature, the coefficients K, A, B, and A shown in FIG. It is represented by the following equation (X) using C, D, E and F. The same applies to the following embodiments. Note that "En" means "10 to the power of n".
^{X = (1 / R) Y} 2 / [1+ {1- (1 + K) (1 / R) 2 Y 2} 1/2]
+ AY ⁴ + BY ⁶ + CY ⁸ + DY ¹⁰ + EY ¹² + FY ¹⁴ ... (X)

FIGS. 5 to 7 show various aberrations when the lens system 10 is focused on infinity, a standard distance, and the closest distance. 5 (a), 6 (a) and 7 (a) show spherical aberration, astigmatism and distortion, and FIGS. 5 (b), 6 (b) and 7 (b) Aberration is shown. The spherical aberrations are wavelength 435.8 nm (two-dot chain line), wavelength 486.1 nm (single-dot chain line), wavelength 546.1 nm (dashed line), wavelength 587.6 nm (solid line), and 656.3 nm (long broken line). Are shown. Astigmatism indicates a tangential ray T and a sagittal ray S. Further, the transverse aberration is shown for each of the tangential ray and the sagittal ray for the same wavelength as described above.

The values of the lens system 10 of the present example and the values of each condition are as follows.
Focal length f1: of the first lens group G1 is −131.56 mm
Focal length f2 of the second lens group G2: 135.28 mm
Focal length f3 of third lens group G3: 113.40 mm
Focal length f4 of fourth lens group G4: 66.61 mm
Moving distance FL of second lens group G2: 17.02 mm
Moving distance FL2 of third lens group G3: 5.51 mm
Focal length B1f of the first cemented lens B1: 135.28 mm
Focal length B2f of the second cemented lens B2: -85.57 mm
Focal length B3f of the third cemented lens B3: -168.27 mm
Focal length B4f of the fourth cemented lens B4: -21148.18 mm
Condition (1) (f2 / f3): 1.19
Condition (2) (FL1 / FL2): 3.09
Condition (3) (B1D> B2D, B3D <B4D
(D7> D14, D18 <D23)):
(53.18> 45.56, 31.60 <31.72)
Condition (4) (| B1p-B1m | <| B2p-B2m |,
| B3p-B3m |> | B4p-B4m |):
(| 44.20-25.43 | <| 94.66-34.71 |,
| 81.55-31.08 |> | 40.77-34.71 |)
Condition (5) (| g4fr / g3er | (| r18 / r16 |)): 3.08
Condition (6) (B3f / B2f): 1.97
Condition (7) (| B3er / Lbfr | (| r20 / r21 |)): 1.51
Condition (8) (| Lber / B4fr | (| r22 / r23)): 1.04
Condition (9) (Ld41 / Ld43 (d20 / d22)): 11.29
Condition (10) (Ld41 / Ld42 (d20 / d21)): 0.70
Condition (11) (| f2 / f1 |): 1.03
Condition (12) (Ld12 / Ld1 (d2 / d1)): 0.45

As described above, the lens system 10 shown in FIG. 1 is a compact lens system having a fixed length, and is a lens system having four groups and sixteen lenses. It is a lens system that is small and easy to handle (manage). Further, in the lens system 10, the FNo is fixed at the time of focusing, so that focusing is easy, and a clear or desired focusing and an image with a small fluctuation in brightness can be obtained. Further, the lens system 10 satisfies the conditions (1) to (12). Further, as shown in FIGS. 5 to 7, it is possible to obtain an image in which various aberrations are satisfactorily corrected in the entire focusing area.

In the lens system 10, the focusing is performed by the second lens group G2 and the third lens group G3 arranged on the object side 11 of the stop St, and is separated from the stop St to adjust the focal length ( Mechanism) can be concentrated in front of the stop St. Therefore, these mechanisms can also be simplified, and a lightweight, high-performance, compact lens system 10 and imaging apparatus 1 can be provided.

FIG. 8 shows a different example of the image pickup apparatus 1. This imaging device (camera) 1 is also disposed on an optical system (imaging optical system, imaging optical system, lens system) 10 and on an image plane side (image side, imaging side, imaging side) 12 of the lens system 10. An image pickup device (image pickup device, image plane) 5. The lens system 10 is an optical system for imaging, and is a lens system having four groups and 15 elements. FIG. 8A shows a lens arrangement where the focus position is at infinity, and FIG. 8B shows a lens arrangement where the focus position is closest (close distance, 630 mm).

This lens system 10 also has a four-group configuration, with the first lens group G1 having the most negative combined refractive power (power) on the object side 11 and the fourth lens group G1 having the most positive combined refractive power (power) on the image plane side 12. Is a fixed lens group that does not move during focusing and does not change the distance to the image plane 5. Also, the stop (aperture stop) St arranged on the object side 11 of the fourth lens group G4 is fixed without changing the distance to the image plane 5. The second lens group G2 having a positive refractive power and disposed on the image plane side 12 of the first lens group G1 monotonously moves to the image plane side 12 when the focus position moves from infinity to the closest. The third lens group G3 having a positive refractive power and disposed on the image plane side 12 of the second lens group G2 monotonously moves to the object side 11 when the focus position moves from infinity to the closest.

FIG. 9 shows data of each lens constituting the lens system 10. FIG. 10 shows the focal length, the F value, and the values of the variable intervals d6, d9, and d16 when the focal length is infinity, standard (2280 mm), and closest (630 mm). FIG. 11 shows aspherical coefficients included in the lens system 10. In this example, the surface S25 of the image surface side 12 of the negative meniscus lens L46 on the image surface side 12 of the fourth lens group G4 is aspheric.

FIGS. 12 to 14 show the spherical aberration, astigmatism, distortion, and lateral aberration of the lens system 10 when the focal length is infinity, standard, and closest. FIGS. 12 (a), 13 (a) and 14 (a) show spherical aberration, astigmatism and distortion, and FIGS. 12 (b), 13 (b) and 14 (b) Aberration is shown.

The basic configuration of the lens system 10 is common to the lens system 10 shown in FIG. The first lens group G1 is a lens group of negative power which is fixed to the object side 11 most (does not move at the time of focusing), and is arranged in order from the object side 11 and is a positive lens convex to the object side 11. It has a meniscus lens L11 having a refractive power, a meniscus lens L12 having a negative refractive power convex on the object side 11, and a negative lens L13 having a biconcave shape, and has a positive-negative-negative power arrangement. The second lens group G2 having a positive refractive power, which moves to the image plane side 12 so as to increase the distance d6 from the first lens G1 along the optical axis 15 during focusing from infinity to the closest, 11, a biconcave negative lens L21 and a biconvex positive lens L22 are provided. The negative lens L21 and the positive lens L22 have a negative-positive power arrangement. A first cemented lens B1 having a positive refractive power is formed.

At the time of focusing from infinity to the closest distance, the lens moves to the object side 11 along the optical axis 15 so as to reduce the distance between the first lens G1 and the second lens group G2. The lens group G3 includes, in order from the object side 11, a meniscus lens L31 having a positive refractive power convex on the object side 11, a meniscus lens L32 having a positive refractive power convex on the object side 11, and The positive lens has a positive refractive power meniscus lens L33 and a concave negative refractive power meniscus lens L34 on the image side 12, and has a positive-positive-positive-negative power arrangement. The positive meniscus lens L33 and the negative meniscus lens L34 constitute a second cemented lens B2 having a negative refractive power that is convex on the object side 11 (concave on the image plane side 12) as a whole.

The fourth lens group G4 having a positive refractive power and disposed closest to the image plane 12 includes a biconcave negative lens L41, a biconvex positive lens L42, and a biconcave , A biconvex positive lens L44, a negative meniscus lens L45 convex on the image side 12, and a biconvex positive lens L46. It has a negative-positive power arrangement. The negative lens L41 and the positive lens L42 constitute a third cemented lens B3 having a negative refractive power that is concave on the object side 11 (convex on the image plane side 12) as a whole. Further, adjacent to the image plane side 12 of the third cemented lens B3, the biconcave negative lens L43 and the biconvex positive lens L44 are generally concave to the object side 11 (convex to the image plane side 12). A fourth cemented lens B4 having a negative refractive power is configured. Therefore, in the lens system 10, a positive meniscus lens having a convex surface on the image plane side 12 disposed between the third cemented lens B3 and the fourth cemented lens B4 is different from the lens system shown in FIG. This is omitted, and the fourth cemented lens B4 is a cemented lens having a positive refractive power as a whole.

A stop St is disposed on the object side 11 of the fourth lens group G4. The stop St is such that the second cemented lens B2 is disposed on the object side 11 without interposing another lens, and the stop St is disposed on the image plane side 12. The third cemented lens B3 is arranged without interposing another lens.

As shown in FIG. 10, the lens system 10 of this embodiment is also a medium telephoto lens having a focus range from infinity to the closest distance of 630 mm and a focal length at infinity of 95 mm. The lens system 10 has a total of 15 lenses, and has a total length (distance from the lens surface closest to the object side 11 to the lens surface closest to the image side 12) LA of 129.9 mm and a distance to the imaging surface 5 of 176.68 mm. This is a more compact lens system, and is an inner focus type lens system in which the second lens group G2 and the third lens group G3 move during focusing. The F-number at each focal length is a constant and small value of 1.68, and the lens system does not move and the F-number does not fluctuate during focusing (focusing).

The numerical values of the lens system 10 and the values of each condition are as follows. In the lens system 10 of the present example, since the fourth cemented lens B3 and the fourth cemented lens B4 are adjacent to each other in the fourth lens group G4 and the positive meniscus lens is omitted, the condition (7) is satisfied. ) To (10) are not subject to evaluation.
Focal length f1 of first lens group G1: -132.25 mm
Focal length f2 of the second lens group G2: 139.90 mm
Focal length f3 of third lens group G3: 110.39 mm
Focal length f4 of fourth lens group G4: 65.94 mm
Moving distance FL of second lens group G2: 17.40 mm
Moving distance FL2 of third lens group G3: 5.39 mm
Focal length B1f of the first cemented lens B1: 139.90 mm
Focal length B2f of the second cemented lens B2: -87.21 mm
Focal length B3f of the third cemented lens B3: -252.93 mm
Focal length B4f of the fourth cemented lens B4: 247.56 mm
Condition (1) (f2 / f3): 1.27
Condition (2) (FL1 / FL2): 3.23
Condition (3) (B1D> B2D, B3D <B4D
(D7> D14, D18 <D21)):
(53.16> 45.66, 31.36 <31.80)
Condition (4) (| B1p-B1m | <| B2p-B2m |,
| B3p-B3m |> | B4p-B4m |):
(| 44.20-25.43 | <| 94.66-34.71 |,
| 81.55-31.08 |> | 40.77-34.71 |)
Condition (5) (| g4fr / g3er | (| r18 / r16 |)): 2.71
Condition (6) (B3f / B2f): 2.90
Condition (11) (| f2 / f1 |): 1.06
Condition (12) (Ld12 / Ld1 (d2 / d1)): 0.52

As described above, the lens system 10 shown in FIG. 8 is a compact lens system having a fixed length, and is a lens system having four groups and 15 elements. It is a lens system that is small and easy to handle (manage). Further, also in the lens system 10, the FNo is fixed at the time of focusing, so that focusing can be easily performed, and a clear or desired focusing and an image with little fluctuation in brightness can be obtained. Further, the lens system 10 satisfied the conditions (1) to (6), (11) and (12), and various aberrations were satisfactorily corrected in the entire focusing region as shown in FIGS. Images can be obtained.

Also in this lens system 10, focusing is performed by the second lens group G2 and the third lens group G3 arranged on the object side 11 of the stop St, and is separated from the stop St to adjust the focal length ( Mechanism) can be concentrated in front of the stop St. Therefore, these mechanisms can also be simplified, and a lightweight, high-performance, compact lens system 10 and imaging apparatus 1 can be provided.

Claims

An imaging lens system,
A first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a positive lens having a positive refractive power arranged in order from the object side. And a fourth lens group.
During focusing from infinity to the nearest, the distance between the first lens group and the second lens group along the optical axis increases, and the distance between the second lens group and the third lens group Wherein the fourth lens group is fixed to an image plane together with a stop arranged on the object side of the fourth lens group.
2. The lens system according to claim 1, wherein a focal length f2 of the second lens group and a focal length f3 of the third lens group satisfy the following condition.
1.0 ≦ f2 / f3 ≦ 1.5
In claim 1 or 2,
During focusing from infinity to the closest, the first lens group is fixed with respect to the image plane, the second lens group moves toward the image plane, and the third lens group moves toward the object side. Go to the lens system.
In claim 3,
A lens system, wherein the movement amount FL1 of the second lens group and the movement amount FL2 of the third lens group satisfy the following conditions.
2.5 ≦ FL1 / FL2 ≦ 4.5
In any one of claims 1 to 4,
A lens system, wherein the second lens group includes a first cemented lens, and the third lens group includes a second cemented lens.
In claim 5,
The lens system, wherein the third lens group includes at least one meniscus lens having a positive refractive power that is convex on the object side and disposed on the object side of the second cemented lens.
The lens system according to claim 6, wherein the first cemented lens is a meniscus lens convex on the image side, and the second cemented lens is a meniscus lens convex on the object side.
In any one of claims 5 to 7,
The lens system, wherein the fourth lens group includes a third cemented lens arranged on the object side and a fourth cemented lens arranged on the image plane side.
In claim 8,
The effective diameter B1D of the first cemented lens, the effective diameter B2D of the second cemented lens, the effective diameter B3D of the third cemented lens, and the effective diameter B4D of the fourth cemented lens are as follows: A lens system that meets the requirements.
B1D> B2D
B3D <B4D
In claim 8 or 9,
The difference between the Abbe number B1p of the lens having a positive refractive power of the first cemented lens and the Abbe number B1m of the lens having a negative refractive power, and the Abbe number B2p of the lens having a positive refractive power of the second cemented lens And the difference between the Abbe number B3m of the lens having a positive refractive power of the third cemented lens and the Abbe number B3m of the lens having a negative refractive power. A lens system wherein the difference between the Abbe number B4p of the positive refractive power lens and the Abbe number B4m of the negative refractive power lens of the fourth cemented lens satisfies the following condition.
| B1p-B1m | <| B2p-B2m |
| B3p-B3m |> | B4p-B4m |
In any one of claims 1 to 4,
The third lens group is a cemented lens disposed on the object side of the diaphragm closest to the image plane, and includes a cemented lens whose surface on the image plane side includes a concave surface on the object side.
A fourth lens group including a cemented lens disposed closest to the image plane side of the diaphragm on the object side, wherein the object-side surface includes a cemented lens including a concave surface on the image plane side; .
In any one of claims 1 to 11,
A lens system, wherein a focal length f1 of the first lens group and a focal length f2 of the second lens group satisfy the following condition.
1.0 ≦ | f2 / f1 | ≦ 1.15
In any one of claims 1 to 12,
The lens system according to claim 1, wherein the first lens group includes a first lens having a meniscus having a positive refractive power convex to the object side and closest to the object side.
In claim 13,
The first lens group includes a second lens having a negative refractive power disposed adjacent to the positive meniscus lens. The first lens group has a thickness Ld1 on the optical axis of the first lens and the first lens. A lens system, wherein a distance Ld12 on the optical axis between the lens and the second lens satisfies the following condition.
0.35 ≦ Ld12 / Ld1 ≦ 0.70
A lens system according to any one of claims 1 to 14,
An imaging device comprising: an imaging element arranged on an image plane side of the lens system.