Inner focus optical system

Abstract

To provide an inner-focus optical system which has a light-weight focusing lens group, exhibits less image height variation when the focusing lens group is wobbled in an optical axis direction, and offers a bright F-number of 1.4 and a view angle corresponding to a 35 mm-equivalent focal length of 40 mm.SOLUTION: An inner-focus optical system disclosed herein comprises, in order from the object side to the image side, a first lens group G1 having negative refractive power, an aperture stop S, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power, the first lens group G1 consisting of, in order from the object side to the image side, a 1a lens group G1a consisting of a single positive lens, a 1b lens group G1b consisting of two negative lenses, and a 1c lens group G1c consisting of a single positive lens. The inner-focus optical system is configured such that the third lens group G3 moves toward the image side while shifting focus from a side of an object at infinity to a side of a nearby object.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical system suitable for a photographing lens used in an imaging device such as a still camera or a video camera. The inner focus method suitable for an autofocus camera is adopted, and when the focus lens group is slightly vibrated (wobbled) in the direction along the optical axis, the image height change rate is small, the F value is as bright as 1.4, and it is related to an inner focus optical system having an angle of view equivalent to 40 mm in terms of 35 mm format focal length.

Background Art

[0002] Conventionally, a retrofocus type has been used for wide-angle lenses used in photographic cameras and still video cameras. This is for a single-lens reflex system adopting a mirror-up mechanism to ensure a back focus of a certain level or more.

[0003] In recent years, mirrorless single-lens type cameras, which have become popular, are frequently used for video shooting. Therefore, for their autofocus method, an inner focus method in which the focus lens group is continuously slightly vibrated (wobbled) in the direction along the optical axis to continuously determine the focus drive direction is often adopted. At that time, if the image height change rate during wobbling is large, the viewer will recognize the magnification change of the subject shown on the screen and feel it annoying. Therefore, a focus method with a small image height change rate with respect to the focus change is required.

[0004] In response to such requirements, Patent Document 1 discloses a large-aperture lens that consists of a first lens group G1 with a positive refractive power, a second lens group G2 with a negative refractive power, and a third lens group G3 with a positive refractive power, arranged in order from the object side. The aperture stop is disposed between the first lens group G1 and the second lens group G2, and focusing is performed by moving the second lens group G2 toward the image plane side. By satisfying predetermined conditions, a high-performance large-aperture lens is achieved with a simple configuration that can adapt to autofocus during video shooting. It reduces the weight of the focus lens group, has little aberration variation due to focusing, and can be adapted to a brightness of about f-number 1.4 using the inner focus method.

[0005] Also, Patent Document 2 discloses an imaging optical system that consists of a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power, arranged in order from the object side. When focusing from an infinite object to a close object, the second lens group G2 moves toward the object side, and the first lens group G1 and the third lens group G3 are fixed with respect to the image plane I. The first lens group G1 includes a diaphragm S and consists of a predetermined lens group, and the third lens group G3 consists of a predetermined lens group. By satisfying a predetermined conditional expression, the distance between the imaging optical system and the imaging device is shortened, miniaturization is achieved, the F-number is small, the light emission angle can be suppressed, and various aberrations are well corrected from infinite shooting to close shooting, and the imaging angle is about 40 to 60°.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the lens system disclosed in Patent Document 1, since the focus lens group and the aperture are adjacent to each other, when the focus lens group for autofocus during video shooting is slightly vibrated (wobbled) in the direction along the optical axis, the image height change rate is large. Therefore, there is a problem that the viewer recognizes the magnification fluctuation of the subject reflected on the screen and feels it annoying.

[0008] Also, in Patent Document 2, since the F value is about 1.8, the amount of blurring is small, and further increasing the aperture Ratio is an issue. Furthermore, since the focus lens group is composed of three lenses including a cemented lens, in order to increase the aperture and perform autofocus while slightly vibrating, the weight reduction of the focus lens group is not sufficient. Ratio Therefore, the present invention provides an inner focus optical system that is lightweight in the focus lens group, has a small image height change rate when the focus lens group is slightly vibrated (wobbled) in the direction along the optical axis, has a bright F value of 1.4, and has an angle of view equivalent to 40 mm in terms of the 35 mm format focal length.

[0009]

Means for Solving the Problems

[0010] and is characterized by satisfying the following conditions In order to solve the above problems, a first invention related to the inner focus optical system of the present invention comprises, in order from the object side to the image side, a first lens group G1 having a negative refractive power, an aperture stop S, a second lens group G2 having a positive refractive power, a third lens group G3 having a negative refractive power, and a fourth lens group G4 having a positive refractive power. The first lens group G1 comprises, in order from the object side to the image side, a first a lens group G1a consisting of a positive single lens, a first b lens group G1b consisting of two negative lenses, and a first c lens group G1c consisting of a positive single lens. When focusing from an infinite object side to a near-distance object side, the third lens group G3 moves toward the image side. to. (1) -0.59 < f / f1 < -0.11 However f: Focal length in the infinity focus state of the entire system f1: Focal length of the first lens group G1 ​

[0011] The second invention related to the inner focus optical system of the present invention is characterized by satisfying the following conditions 。 (2) 0.55 < f / f2 < 2.55 (3) -1.56 < f / f3 < -0.29 (4) 0.18 < f / f4 < 0.90 (5) -2.48 < f / f1b < -0.44 (6) 0.11 < f / f1c < 0.83 However, f: Focal length in the infinity focus state of the entire system Separation f2: Focal length of the second lens group G2 f3: Focal length of the third lens group G3 f4: Focal length of the fourth lens group G4 f1b: Focal length of the first b lens group G1b f1c: Focal length of the first c lens group G1c

[0012] The third invention related to the inner focus optical system of the present invention is characterized by satisfying the following conditions. (7) 0.25 < M4 < 1.0 However, M4: Magnification burden of the fourth lens group G4 when the object distance is infinite

[0013] The fourth invention related to the inner focus optical system of the present invention is characterized by satisfying the following conditions. (8) 0.67 < |(M4^2 × (1 - M3^2))| < 3.78 However, M3: Magnification burden of the third lens group G3 when the object distance is infinite M4: Magnification burden of the fourth lens group G4 when the object distance is infinite

[0014] The fifth invention related to the inner focus optical system of the present invention is characterized in that the third lens group G3 having a negative refractive power is composed of a single lens.

[0015] The sixth invention related to the inner focus optical system of the present invention is characterized by satisfying the following conditions. (9) 2.47 < D / Y < 10.72 However, D: The length from the aperture to the image plane Y: The maximum image height

[0016] The seventh invention related to the inner focus optical system of the present invention is characterized by satisfying the following conditions. (10) 55 < VdG1b However, VdG1b: The average Abbe number of the first lens group G1b

Effect of the Invention

[0017] According to the present invention, an inner focus method suitable for an autofocus camera is adopted, and when the focus lens group is slightly vibrated (wobbled) in the direction along the optical axis, the image height change rate is small, the F value is as bright as 1.4, and an inner focus optical system having an angle of view equivalent to 40 mm in terms of the 35 mm film size can be provided.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 30

Mode for Carrying Out the Invention

[0019] Hereinafter, the inner focus optical system of the present embodiment will be described. Note that the following description of the examples is an example of the optical system of the present invention, and the present invention is not limited to the present examples without departing from the gist thereof.

[0020] As can be seen from the lens configuration diagrams shown in FIGS. 1, 6, 11, 16, 21, and 26, the inner focus optical system of the present invention includes, in order from the object side to the image side, a first lens group G1 with negative refractive power, an aperture stop S, a second lens group G2 with positive refractive power, a third lens group G3 with negative refractive power, and a fourth lens group G4 with positive refractive power. The first lens group G1 includes, in order from the object side to the image side, a first a lens group G1a composed of a positive single lens, a first b lens group G1b composed of two negative single lenses, and a first c lens group G1c composed of a positive single lens. When focusing from an infinite object side to a near-distance object side, the third lens group G3 moves toward the image side.

[0021] The reason why the above configuration is necessary is as follows. That is, by gently refracting the off-axis chief ray incident on the first lens surface at a large angle with respect to the optical axis with the first lens group G1 having negative refractive power and emitting it to the aperture surface, and further gently refracting it with the second lens group G2 having positive refractive power, it is possible to reduce the inclination angle of the off-axis chief ray incident on the third lens group G3, which is the focus lens group, and contribute to the reduction of the image height change rate.

[0022] Also, by disposing the aperture between the first lens group G1 and the second lens group G2 and separating the position of the aperture from the image plane as much as possible, the incident angle of the off-axis chief ray reaching the imaging device can be reduced, shading problems can be suppressed, and the change rate of image height when the focus group is slightly vibrated (wobbled) during focusing can be reduced.

[0023] Also, by making the second lens group G2 on the image side of the aperture have a positive refractive power, the angle of the off-axis chief ray incident on the subsequent focus lens group with respect to the optical axis can be reduced, which contributes to reducing the change rate of image height when the focus group is slightly vibrated (wobbled) during focusing.

[0024] Also, by disposing the fourth lens group G4 with positive refractive power, it is not necessary to increase the positive refractive power of the combined system of the first lens group G1 and the second lens group G2, so it is possible to suppress the occurrence of spherical aberration, coma aberration, etc.

[0025] Also, by making the first a lens group G1a have a positive refractive power, it is possible to suppress an excessive deterioration of negative distortion aberration and a positive field curvature by a retro type in which the first lens group G1 has a negative refractive power and the second lens group G2 or later has a positive refractive power. In order to give such an effect and further suppress an increase in the overall length and outer diameter, it is desirable to configure the first a lens group G1a with a single lens.

[0026] Also, since the first b lens group G1b has a strong negative refractive power, it is necessary to control the spherical aberration which is its residual aberration. Further, in the present invention, in order to give the first b lens group G1b a role of controlling the decentered coma aberration, it is necessary to control the difference between the product of the paraxial marginal ray inclination angle and the coma aberration coefficient and the product of the paraxial chief ray inclination angle and the spherical aberration coefficient. By configuring the first b lens group G1b with two negative lenses, it becomes possible to easily perform such control.

[0027] In addition, since the first lens group G1c receives the on-axis light beam diverged by the first lens group G1b, by providing a positive refractive power, it becomes possible to suppress the aperture stop and the height of the on-axis light beam to the subsequent group. Further, in the present invention, in order to give the first lens group G1c a role of controlling the tilt of the image plane due to decentration, it is necessary to control the difference between the product of the paraxial marginal ray angle and the image plane curvature aberration coefficient and the astigmatism coefficient, and the product of the paraxial chief ray angle and the coma aberration coefficient. By configuring the first lens group G1c with a positive single lens, it becomes possible to facilitate their control.

[0028] In addition, by configuring the first lens group G1 with the above three sub-units of positive, negative, and positive, it becomes easier to control the behavior of the lower light ray of the off-axis light beam, and it is possible to improve the optical performance.

[0029] In addition, the third lens group G3 is a focusing group and it is desirable to be configured with a small number of lenses for weight reduction. However, the aberration correction is not sufficient and it becomes a cause of aberration generation. In particular, since the third lens group G3 with negative refractive power is arranged at a position where the height of the off-axis chief ray is large, it becomes a cause of positive astigmatism, magnification chromatic aberration, and positive distortion aberration. Therefore, by arranging the fourth lens group G4 with positive refractive power at a position where the height of the off-axis chief ray is large, it becomes possible to effectively correct these aberrations.

[0030] From these, it becomes possible to provide an inner focus optical system in which the change rate of the image height when the focus lens group is slightly vibrated (wobbled) in the direction along the optical axis is small, and which has an angle of view equivalent to 40 mm in terms of the 35 mm format conversion focal length.

[0031] Furthermore, it is preferable that the inner focus optical system of the present embodiment satisfies the following conditional expressions. (1) -0.79 < f / f1 < -0.11 (2) 0.55 < f / f2 < 2.55 (3) -1.56 < f / f3 < -0.29 (4) 0.18 < f / f4 < 0.90 (5) -2.48 < f / f1b < -0.44 (6) 0.11 < f / f1c < 0.83 However, f: Focal length in the infinity focus state of the entire system f1: Focal length of the first lens group G1 f2: Focal length of the second lens group G2 f3: Focal length of the third lens group G3 f4: Focal length of the fourth lens group G4 f1b: Focal length of the first b lens group G1b f1c: Focal length of the first c lens group G1c

[0032] In conditional expression (1), by appropriately defining the ratio of the focal length of the first lens group G1 to the focal length of the entire system, the incident angle of the peripheral field angle can be relaxed and transferred to the subsequent optical system. Also, the increase in the aperture diameter can be suppressed, and it becomes possible to suppress the occurrence of spherical aberration, coma aberration, etc. due to the increase in aperture size. Ratio

[0033] When the negative refractive power of the first lens group G1 becomes large beyond the lower limit of conditional expression (1), it becomes difficult to suppress the aperture diameter. Also, it becomes a cause of positive spherical aberration within the first lens group. Also, since the incident angle and ray height of the on-axis ray to the second lens group increase, it becomes a cause of higher-order aberration, making aberration correction difficult. Also, since the back focus becomes long, the overall length of the optical system also becomes long.

[0034] On the other hand, when the negative refractive power of the first lens group G1 becomes small beyond the upper limit of conditional expression (1), the inclination of the lower ray passing through the aperture stop S is not relaxed, so it becomes difficult to correct the coma flare of the lower ray.

[0035] Regarding conditional expression (1), preferably, by limiting its lower limit value to -0.59 and its upper limit value to -0.15, the above-mentioned effects can be made more certain.

[0036] In conditional expression (2), by appropriately defining the ratio of the focal length of the second lens group G2 to the focal length of the entire system, the overall optical length, the suppression of the increase in the image height change rate, and the large aperture RatioSuppress the occurrence of spherical aberration and coma aberration due to aberration.

[0037] When the positive refractive power of the second lens group G2 becomes smaller beyond the lower limit of the conditional expression (2), the angle of the off-axis chief ray incident on the third lens group G3, which is the focus lens group, with respect to the optical axis cannot be made smaller. Therefore, when the focus group is slightly vibrated (wobbled) during focusing, the image height change rate becomes large, which is not preferable. Also, in order to maintain the focal length of the entire system, it is necessary to reduce the negative refractive power of the third lens group G3, and since the movement amount of the third lens group G3 during focusing increases, the overall length of the optical system becomes large, which is not preferable.

[0038] On the other hand, when the positive refractive power of the second lens group G2 becomes larger beyond the upper limit of the conditional expression (2), it becomes difficult to correct spherical aberration and coma aberration during large aperture Ratio aberration.

[0039] Regarding the conditional expression (2), preferably, by limiting the lower limit value to 0.73 and the upper limit value to 1.91, the above-described effects can be made more certain.

[0040] In the conditional expression (3), by appropriately defining the ratio of the third lens group G3, which is the focus lens group, to the focal length of the entire system at infinity focus, it becomes possible to suppress the aberration variation during focusing.

[0041] When the negative refractive power of the third lens group G3 becomes larger beyond the lower limit of the conditional expression (3), the movement amount of the third lens group G3 during focusing becomes smaller, which is advantageous in terms of space, but it becomes difficult to correct the variations in spherical aberration and astigmatism during focusing simultaneously.

[0042] On the other hand, when the negative refractive power of the third lens group G3 becomes smaller beyond the upper limit of the conditional expression (3), the movement amount of the third lens group G3 during focusing becomes larger, and the overall length of the optical system becomes larger. Also, the amplitude amount during wobbling must be increased, which applies a load to the actuator, which is not preferable.

[0043] Regarding the conditional expression (3), preferably, by limiting its lower limit value to -1.17 and its upper limit value to -0.39, the above-described effects can be made more certain.

[0044] In the conditional expression (4), by appropriately defining the ratio of the focal length of the fourth lens group G4 to the focal length of the entire system, it becomes possible to correct the remaining aberration up to the focus lens group and improve the performance of the entire system.

[0045] When the positive refractive power of the fourth lens group G4 becomes smaller beyond the lower limit of the conditional expression (4), the imaging magnification of the fourth lens group G4 becomes larger, and the reduction effect of the residual image aberration up to the focus lens group becomes smaller, making it difficult to improve the performance.

[0046] On the other hand, when the positive refractive power of the fourth lens group G4 becomes larger beyond the upper limit of the conditional expression (4), the imaging magnification of the fourth lens group becomes in the shrinking direction, and aberration correction becomes easier, but the entire system becomes larger, which is not preferable.

[0047] Regarding the conditional expression (4), preferably, by limiting its lower limit value to 0.24 and its upper limit value to 0.68, the above-described effects can be made more certain.

[0048] In the conditional expression (5), by appropriately defining the ratio of the focal length of the entire system to the focal length of the first b lens group G1b, it becomes possible to suppress spherical aberration and field curvature in a large aperture ratio lens, and at the same time, it becomes possible to correct the decentered coma aberration of the entire system caused by manufacturing variations by decentering the first b lens group G1b.

[0049] When the negative refractive power of the first lens group G1b exceeds the lower limit of conditional expression (5), it becomes difficult to reduce the aperture diameter. Also, spherical aberration and field curvature become excessive and correction becomes difficult. Further, since the decentration sensitivity of the first lens group G1b becomes too large, it becomes difficult to perform correction to restore the optical performance. Moreover, since the residual spherical aberration and residual coma aberration of the first lens group G1b increase, it becomes difficult to cancel out these aberrations in the second lens group and subsequent groups. Also, in order to maintain the overall focal length of the entire system, the magnification of the combined system after the second lens group has to be increased, and since the residual spherical aberration, coma aberration, astigmatism, and field curvature deteriorated in the first lens group G1b are multiplied, it becomes even more difficult to perform aberration correction.

[0050] On the other hand, when the negative refractive power of the first lens group G1b becomes smaller than the upper limit of conditional expression (5), spherical aberration and field curvature become insufficient and it becomes difficult to achieve good aberration correction. Also, the effect of correcting the overall decentration coma aberration caused by manufacturing variations by decentering the first lens group G1b becomes weak, which is not preferable. Further, the adjustment amount for correction becomes large, and it becomes necessary to increase the diameter of the first lens G1b and ensure the clearance in the axial direction, which is not preferable because the entire optical system becomes large.

[0051] Regarding conditional expression (5), preferably, by limiting its lower limit value to -1.86 and its upper limit value to -0.59, the above-described effects can be made more certain.

[0052] In conditional expression (6), by appropriately defining the ratio of the overall focal length of the entire system to the focal length of the first lens group G1c, it becomes possible to suppress field curvature, astigmatism, and coma aberration in a large aperture ratio lens, and it also becomes possible to correct the overall one-sided defocus caused by manufacturing variations by decentering the first lens group G1c.

[0053] When the positive refractive power of the first c - lens group G1c becomes smaller than the lower limit of conditional expression (6), the field curvature becomes excessive and it becomes difficult to achieve good correction. Also, the effect of correcting the overall single - sided defocus caused by manufacturing variations by decentering the first c - lens group G1c becomes weak, which is not preferable. Moreover, the adjustment amount for correction increases, the diameter of the first c - lens G1c needs to be increased, and an axial clearance needs to be ensured, which is not preferable because the entire optical system becomes larger.

[0054] On the other hand, when the positive refractive power of the first c - lens group G1c becomes larger than the upper limit of conditional expression (6), the field curvature becomes insufficient and it becomes difficult to achieve good correction. Also, since the decentering sensitivity of the first c - lens group G1c becomes too large, decentering adjustment becomes difficult.

[0055] Regarding conditional expression (6), preferably, by limiting its lower limit value to 0.15 and its upper limit value to 0.62, the above - mentioned effects can be made more certain.

[0056] Furthermore, it is desirable that the inner - focus optical system of the present invention satisfies the following conditional expressions. (7) 0.25 < M4 < 1.0 However, M4: Magnification burden of the fourth lens group G4 when the object distance is infinite

[0057] Conditional expression (7) defines the imaging magnification of the fourth lens group G4. By making the imaging magnification of the fourth lens group G4, which is the final lens group of the inner - focus optical system of the present invention, a reduction system, it is possible to increase the performance of the entire system without multiplying the residual aberration up to the focus lens group.

[0058] When the imaging magnification of the fourth lens group G4 becomes smaller than the lower limit of conditional expression (7), the residual aberration up to the focus group is reduced, but the entire system becomes larger, which is not preferable.

[0059] On the other hand, when the imaging magnification of the fourth lens group G4 exceeds 1 and exceeds the upper limit of conditional expression (7), the residual aberration up to the focus lens group expands, so it becomes difficult to correct that aberration.

[0060] Regarding the conditional expression (7), preferably, by limiting the lower limit value thereof to 0.34 and the upper limit value to 0.87, the above-described effects can be made more certain.

[0061] Furthermore, it is desirable that the inner focus optical system of the present invention satisfies the conditional expression shown below. (8) 0.67 < |(M4^2 × (1 - M3^2))| < 3.78 However, M3: Magnification burden of the third lens group G3 when the object distance is infinite M4: Magnification burden of the fourth lens group G4 when the object distance is infinite

[0062] The conditional expression (8) defines the sensitivity of the imaging surface when the third lens group G3 moves during focusing. By appropriately defining this value, it becomes possible to accurately drive and control the focus lens group within the in-focus range during autofocus.

[0063] When the sensitivity of the imaging surface when moving during focusing exceeds the lower limit of the conditional expression (8) and becomes small, the movement amount of the focus lens group increases. Therefore, the variation in the chief ray height of the focus lens group due to wobbling becomes large, the effect of suppressing the image height variation becomes weak, and it becomes difficult to suppress the image height variation during wobbling.

[0064] On the other hand, when the sensitivity of the imaging surface when moving during focusing exceeds the upper limit of the conditional expression (8) and becomes large, the movement amount of the focus lens group decreases. Therefore, the imaging surface moves greatly with a slight movement of the focus lens group, and it becomes difficult to drive and control the third lens group G3, which is the focus lens group, within the in-focus range during autofocus. In addition, when the sensitivity of the imaging surface increases, that is, when the negative power of the third lens group G3 becomes strong, it becomes difficult to correct aberrations without increasing the number of constituent lenses of the third lens group G3. Increasing the number of constituent lenses leads to an increase in weight, making it difficult to cause minute vibrations (wobbling) during focusing.

[0065] Regarding the conditional expression (8), preferably, by limiting the lower limit value to 0.89 and the upper limit value to 2.84, the above-described effects can be made more certain.

[0066] Furthermore, in the inner focus optical system of the present invention, it is desirable that the third lens group G3 having a negative refractive power consists of a single lens. Thereby, the focus group can be lightened, and miniaturization of the actuator for focus driving and thus miniaturization of the product size can be achieved.

[0067] Furthermore, in the inner focus optical system of the present invention, it is desirable to satisfy the conditional expression shown below. (9) 2.47 < D / Y < 10.72 However, D: The length from the aperture stop S to the image plane Y: The maximum image height

[0068] The conditional expression (9) can suppress the image height variation during wobbling by appropriately defining the ratio of the length from the aperture stop S to the image plane and the maximum image height.

[0069] When the ratio of the length from the aperture stop S to the image plane and the maximum image height becomes smaller than the lower limit value of the conditional expression (9), the incident angle to the off-axis image plane becomes larger, and the variation of the chief ray height of the focus lens group during wobbling becomes larger. Therefore, it becomes difficult to suppress the image height variation during wobbling.

[0070] On the other hand, when the ratio of the length from the aperture stop S to the image plane and the maximum image height becomes larger than the upper limit of the conditional expression (9), the entire optical system becomes large, which is not preferable.

[0071] Regarding the conditional expression (9), preferably, by limiting the lower limit value to 3.29 and the upper limit value to 8.04, the above-described effects can be made more certain.

[0072] Furthermore, in the inner focus optical system of the present invention, it is desirable to satisfy the conditional expression shown below. (10) 55 < VdG1b However, VdG1b: Average Abbe number of the 1b-th lens group G1b

[0073] By appropriately defining the average Abbe number of the first lens group G1b, the conditional expression (10) can suppress the magnification chromatic aberration and the chromatic aberration that deteriorates when the first lens group G1b is used as the centering group.

[0074] When the Abbe number of the first lens group G1b becomes smaller than the lower limit of the conditional expression (10), the magnification chromatic aberration deteriorates, and it becomes difficult to correct this in the entire lens system. Also, when the first lens group G1b is used as the centering group, it becomes difficult to suppress the decentration chromatic aberration.

[0075] Regarding the conditional expression (10), preferably, by limiting its lower limit to 60, the above-described effects can be made more certain.

[0076] In the inner focus optical system of the present invention, it is more effective to have the following configuration.

[0077] In the inner focus optical system of the present invention, the third lens group G3 is configured by a single lens, but by achromatizing the third lens group G3 or giving it an aspherical effect with a cemented lens, a diffractive optical surface, or a metalens structure surface, it is also possible to reduce the chromatic aberration of the entire system and suppress the variations in spherical aberration, coma aberration, and astigmatism of the chromatic aberration due to focus movement.

[0078] Next, each numerical example related to the inner focus optical system of the present invention will be described.

[0079] In [surface data], the surface number is the number of the lens surface or the aperture stop counted from the object side, r is the radius of curvature of each surface, d is the distance between each surface, nd is the refractive index with respect to the d-line (wavelength λ = 587.56 nm), and νd is the Abbe number with respect to the d-line. Also, BF represents the back focus.

[0080] For the numbered (aperture), the radius of curvature ∞ (infinity) with respect to the plane or aperture stop is entered. Also, the refractive index of air n = 1.0000 is omitted from the description.

[0081] [Aspherical data] shows the coefficient values that give the aspherical shape of the lens surface marked with * in [surface data]. The shape of the aspherical surface is such that when the displacement in the direction perpendicular to the optical axis is y, the displacement in the optical axis direction from the intersection of the aspherical surface and the optical axis (sag amount) is z, the conic coefficient is K, and the aspherical coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th orders are A4, A6, A8, A10, A12, A14, and A16 respectively, the coordinates of the aspherical surface are represented by the following formula. TIFF0007711925000001.tif17166

[0082] [Various data] shows values such as the focal length.

[0083] [Variable interval data] shows the variable interval and the values of BF (back focus) in each shooting distance state or each shooting magnification state.

[0084] [Lens group data] shows the surface number of the most object-side surface that constitutes each lens group, the combined focal length of the entire group, the surface number of the most object-side surface of the lens element adjacent to the image side of the aperture stop, and the focal length. In addition, for all the specification values below, the unit of the described focal length f, radius of curvature r, lens surface interval d, and other lengths is millimeter (mm) unless otherwise specified. However, in the optical system, equivalent optical performance can be obtained in both proportional magnification and proportional reduction, so it is not limited to this.

[0085] Also, in the aberration diagrams corresponding to each embodiment, d, g, and C represent the d-line, g-line, and C-line respectively, and ΔS and ΔM represent the sagittal image plane and the meridional image plane respectively. Furthermore, in the lens configuration diagrams shown in FIGS. 1, 6, 11, 16, and 21, S is the aperture stop, FL is the optical filter, I is the image plane, and the one-dot chain line passing through the center is the optical axis.

[0086] Next, the lens configuration of the embodiment according to the inner focus optical system of the present invention will be described. In the following description, the lens configuration will be described in the order from the object side to the image side.

Embodiment

[0087] FIG. 1 is a lens configuration diagram of the inner focus optical system according to Embodiment 1 of the present invention.

[0088] The lens configuration of the inner focus optical system in FIG. 1 is composed of a first lens group G1 with a negative refractive power, a second lens group G2 with a positive refractive power, a third lens group G3 with a negative refractive power, and a fourth lens group G4 with a positive refractive power, in order from the object side to the image side.

[0089] The first lens group G1 is composed of a first a lens group G1a consisting of a positive meniscus lens with a convex surface facing the object side, a first b lens group G1b consisting of a negative meniscus lens with a convex surface facing the object side, a biconcave lens, and a first c lens group G1c consisting of a biconvex lens, in order from the object side to the image side.

[0090] The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

[0091] The second lens group G2 is composed of a biconcave lens, a cemented lens of a biconvex lens with an aspherical surface on the image side, a biconvex lens, and a biconvex lens.

[0092] The third lens group G3 is composed of a negative meniscus lens with a convex surface facing the object side, and focusing from an infinite object to a near object is performed by moving the third lens group G3 along the optical axis toward the image side.

[0093] The fourth lens group G4 is composed of a biconvex lens with aspherical surfaces on both sides and a negative meniscus lens with a convex surface facing the object side.

[0094] The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

[0095] Next, the specifications of the inner focus optical system according to Example 1 are shown below.

[0096] Numerical Example 1 Unit: mm [Surface Data] Surface Number r d nd vd Object Surface ∞ (d0) 1 69.4400 2.2500 2.00069 25.46 2 142.5300 0.4000 3 33.5800 1.2000 1.49700 81.61 4 12.8000 6.2300 5 -100.0000 1.0000 1.43700 95.10 6 33.3700 2.0000 7 75.3300 2.3500 2.05090 26.94 8 -234.6100 5.0700 9 (Aperture) ∞ 4.3100 10 -21.4900 1.0000 1.77047 29.74 11 28.6100 5.8000 1.76450 49.10 12* -37.1900 0.2500 13 186.8400 7.2500 1.59282 68.62 14 -21.4800 0.1500 15 37.8700 6.3900 1.59282 68.62 16 -49.2300 (d16) 17 41.6900 0.8000 1.73037 32.23 18 15.6100 (d18) 19* 35.4100 4.6500 1.80610 40.73 20* -90.0000 0.1500 21 30.4400 1.0000 1.48749 70.44 22 16.2600 15.0000 23 ∞ 4.1400 1.51633 64.14 24 ∞ (BF) Image plane ∞ [Aspherical data] 12 surfaces, 19 surfaces, 20 surfaces K 0.00000 0.00000 0.00000 A4 3.33950E-05 1.88440E-05 1.63120E-05 A6 2.82730E-08 -1.27440E-08 -1.20380E-07 A8 -7.13200E-11 5.31540E-10 1.84370E-09 A10 1.47300E-14 9.63830E-13 -9.72690E-12 A12 -6.10360E-16 -1.51470E-14 3.52060E-14 A14 0.00000E+00 1.88150E-17 -1.80610E-16 A16 0.00000E+00 0.00000E+00 4.73790E-19 [Various data] INF Focal length 20.27 F-number 1.43 Full field angle 2ω 59.01 Image height Y 11.15 Overall lens length 80.26 [Variable interval data] INF Magnification 0.025 d0 ∞ 794.6816 d16 1.4000 1.7647 d18 6.0800 5.7153 BF 1.3929 1.3929 [Lens group data] Group Starting surface Focal length G1 1 -77.32 G2 10 18.43 G3 17 -34.61 G4 19 52.51 G1a 1 133.27 G1b 3 -22.91 G1c 7 54.47

Example

[0097] Figure 6 is a lens configuration diagram of the inner focus optical system according to Embodiment 2 of the present invention.

[0098] The lens configuration of the inner focus optical system in Figure 6 is composed of a first lens group G1 with a negative refractive power, a second lens group G2 with a positive refractive power, a third lens group G3 with a negative refractive power, and a fourth lens group G4 with a positive refractive power, in order from the object side to the image side.

[0099] The first lens group G1 is composed of a first a lens group G1a consisting of a positive meniscus lens with a convex surface facing the object side, a first b lens group G1b consisting of a negative meniscus lens with a convex surface facing the object side and a negative meniscus lens with a convex surface facing the object side, and a first c lens group G1c consisting of a biconvex lens, in order from the object side to the image side.

[0100] The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

[0101] The second lens group G2 is composed of a cemented lens of a biconcave lens and a positive meniscus lens with a convex surface facing the object side, a biconvex lens, and a biconvex lens with aspherical surfaces on both sides.

[0102] The third lens group G3 is composed of a negative meniscus lens with a convex surface facing the object side, and focusing from an infinite object to a near object is performed by moving the third lens group G3 toward the image side along the optical axis.

[0103] The fourth lens group G4 is composed of a biconvex lens with aspherical surfaces on both sides and a negative meniscus lens with a convex surface facing the object side.

[0104] The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

[0105] Subsequently, the specifications of the inner focus optical system according to Example 2 are shown below.

[0106] Numerical Example 2 Unit: mm [Surface Data] Surface No. r d nd vd Object plane ∞ (d0) 1 27.1076 3.3337 2.05090 26.94 2 36.2543 0.5000 3 26.9702 0.8000 1.43700 95.10 4 11.5196 5.4325 5 77.6404 0.8000 1.43700 95.10 6 14.2801 4.8913 7 64.5440 1.9528 1.91082 35.25 8 -319.8676 3.1500 9 (Aperture) ∞ 3.4863 10 -32.7512 0.8000 1.77047 29.74 11 22.4694 3.8784 1.69680 55.46 12 110.9084 1.0000 13 53.6609 8.6689 1.59282 68.62 14 -21.4505 0.1500 15* 22.0277 8.1233 1.59201 67.02 16* -30.0931 (d16) 17 1000.0000 0.8000 1.65412 39.68 18 16.2569 (d18) 19* 90.0000 4.8904 1.80610 40.73 20* -47.2629 0.1500 21 81.8183 0.8000 1.61340 44.27 22 57.2276 11.9396 23 ∞ 4.1400 1.51633 64.14 24 ∞ (BF) Image plane ∞ [Aspherical data] Surface 15, Surface 16, Surface 19, Surface 20 K 0.00000 0.00000 0.00000 0.00000 A4 -1.28646E-05 4.21200E-05 3.19413E-05 2.25233E-05 A6 -5.20148E-09 -8.55724E-08 -1.15895E-07 -1.25731E-07 A8 1.61530E-10 1.30118E-10 5.02168E-10 4.82337E-10 A10 -1.94294E-12 3.97612E-13 2.21260E-13 -3.62175E-13 A12 8.55760E-15 2.37691E-15 -8.05875E-16 -4.48126E-16 [Various data] INF Focal length 19.70 F-number 1.43 Full angle of view 2ω 62.20 Image height Y 11.15 Overall lens length 80.00 [Variable interval data] INF Shooting magnification 0.025 d0 ∞ 767.6277 d16 2.0000 2.2616 d18 6.3128 6.0512 BF 2.0000 2.0000 [Lens group data] Group Starting surface Focal length G1 1 -76.50 G2 10 15.47 G3 17 -25.27 G4 19 44.16 G1a 1 86.15 G1b 3 -20.28 G1c 7 59.11

Example

[0107] FIG. 11 is a lens configuration diagram of the inner focus optical system according to Embodiment 3 of the present invention.

[0108] The lens configuration of the inner focus optical system in FIG. 11 is composed of a first lens group G1 with negative refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with negative refractive power, and a fourth lens group G4 with positive refractive power, in order from the object side to the image side.

[0109] The first lens group G1 is composed of a first a lens group G1a consisting of a positive meniscus lens with a convex surface facing the object side, a first b lens group G1b consisting of a negative meniscus lens with a convex surface facing the object side and a negative meniscus lens with a convex surface facing the object side, and a first c lens group G1c consisting of a biconvex lens, in order from the object side to the image side.

[0110] The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

[0111] The second lens group G2 is composed of a cemented lens of a biconcave lens and a biconvex lens, a biconvex lens with both surfaces being aspherical, and a biconvex lens.

[0112] The third lens group G3 is composed of a negative meniscus lens with a convex surface facing the object side and both surfaces being aspherical, and focusing from an infinite object to a near-distance object is performed by moving the third lens group G3 toward the image side along the optical axis.

[0113] The fourth lens group G4 is composed of a biconvex lens and a negative meniscus lens with an aspherical surface on the object side and a convex surface facing the object side.

[0114] The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

[0115] Subsequently, the specifications of the inner focus optical system according to Example 3 are shown below.

[0116] Numerical Example 3 Unit: mm [Surface data] Surface number r d nd vd Object plane ∞ (d0) 1 25.1720 6.4859 1.92286 20.88 2 41.3762 1.2963 3 38.0950 1.0000 1.59282 68.62 4 12.3596 5.0939 5 36.4870 1.0000 1.51742 52.15 6 12.7142 4.3145 7 56.4719 1.8442 1.91082 35.25 8 -4464.1570 3.9025 9 (Aperture) ∞ 3.5487 10 -28.1661 0.8000 1.85451 25.15 11 22.9981 6.4955 1.72916 54.67 12 -33.4321 1.0000 13* 100.0000 3.7914 1.69350 53.20 14* -28.4737 0.1500 15 70.2589 6.9345 1.59282 68.62 16 -22.8657 (d16) 17* 68.6380 0.9000 1.68948 31.02 18* 16.4548 (d18) 19 68.8366 3.9591 1.92286 20.88 20 -47.4979 0.1500 21* 121.8303 0.8000 1.68948 31.02 22 43.9119 12.1440 23 ∞ 4.1400 1.51633 64.14 24 ∞ (BF) Image plane ∞ [Aspherical data] Surface 13, 14, 17, 18, 21 K 0.00000 0.00000 0.00000 0.00000 0.00000 A4 -4.09990E-05 -3.89783E-06 3.43096E-05 5.16818E-05 6.76689E-06 A6 9.25711E-08 1.16137E-07 -2.69132E-07 -1.75566E-07 1.22001E-07 A8 1.18849E-10 -2.40253E-10 -1.59413E-10 -2.12899E-09 -1.90998E-10 A10 0.00000E+00 1.84014E-12 1.96095E-12 6.34297E-12 5.64571E-13 A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 [Various data] INF Focal length 19.70 F-number 1.44 Full angle of view 2ω 62.53 Image height Y 11.15 Overall lens length 80.00 [Variable interval data] INF Magnification 0.025 d0 ∞ 762.9515 d16 2.0000 2.3724 d18 6.2494 5.8770 BF 2.0000 1.9999 [Lens group data] Group starting surface Focal length G1 1 -61.45 G2 10 16.26 G3 17 -31.61 G4 19 43.74 G1a 1 58.42 G1b 3 -15.89 G1c 7 61.24

Example

[0117] Figure 16 is a lens configuration diagram of the inner focus optical system according to Example 4 of the present invention.

[0118] The lens configuration of the inner focus optical system in Figure 16 is composed of a first lens group G1 with a negative refractive power, a second lens group G2 with a positive refractive power, a third lens group G3 with a negative refractive power, and a fourth lens group G4 with a positive refractive power, in order from the object side to the image side.

[0119] The first lens group G1 is composed of a first a lens group G1a consisting of a positive meniscus lens with a convex surface facing the object side, a first b lens group G1b consisting of a negative meniscus lens with a convex surface facing the object side and a negative meniscus lens with a convex surface facing the object side, and a first c lens group G1c consisting of a positive meniscus lens with a convex surface facing the object side, in order from the object side to the image side.

[0120] The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

[0121] The second lens group G2 is composed of a cemented lens of a biconcave lens and a biconvex lens, a biconvex lens with both surfaces being aspherical, and a biconvex lens.

[0122] The third lens group G3 is composed of a negative meniscus lens with aspherical surfaces on both sides and a convex surface facing the object side, and focusing from an infinite object to a close-distance object is performed by moving the third lens group G3 toward the image side along the optical axis.

[0123] The fourth lens group G4 is composed of a biconvex lens and a negative meniscus lens with an aspherical surface on the object side and a convex surface facing the object side.

[0124] The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

[0125] Subsequently, the specifications of the inner focus optical system according to Example 4 are shown below.

[0126] Numerical Example 4 Unit: mm [Surface Data] Surface number r d nd vd Object plane ∞ (d0) 1 25.0124 5.5155 1.92286 20.88 2 41.5595 1.0370 3 35.5945 1.0000 1.59282 68.62 4 11.9069 4.8268 5 26.9036 1.0000 1.51742 52.15 6 12.6892 3.8802 7 42.0542 2.9548 1.91082 35.25 8 84.1088 3.6971 9 (Aperture) ∞ 3.4647 10 -33.2993 0.8000 1.85451 25.15 11 24.0162 7.0266 1.72916 54.67 12 -31.2211 1.0000 13* 100.0000 3.9575 1.69350 53.20 14* -29.5632 0.1500 15 108.6593 7.0285 1.59282 68.62 16 -22.4796 (d16) 17* 37.9973 1.2214 1.68948 31.02 18* 14.1604 (d18) 19 134.3811 3.3679 1.92286 20.88 20 -41.1924 0.1500 21* 205.6852 1.1000 1.68948 31.02 22 51.5255 11.8595 23 ∞ 4.1400 1.51633 64.14 24 ∞ (BF) Image plane ∞ [Aspherical data] Surface 13, Surface 14, Surface 17, Surface 18, Surface 21 K 0.00000 0.00000 0.00000 0.00000 0.00000 A4 -4.07055E-05 1.04419E-06 3.96316E-05 5.40830E-05 1.18334E-05 A6 3.54212E-08 4.45608E-08 -5.81136E-07 -4.82526E-07 2.00144E-07 A8 1.58763E-09 7.73064E-10 4.43167E-10 -5.08897E-09 -1.03585E-09 A10 -7.95273E-12 -1.93695E-12 5.48820E-12 2.66572E-11 3.24841E-12 A12 1.11536E-14 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 [Various data] INF Focal length 20.30 F-number 1.43 Full angle of view 2ω 60.33 Image height Y 11.15 Overall lens length 80.00 [Variable interval data] Infinity shooting magnification 0.025 d0 ∞ 788.5588 d16 2.0000 2.3775 d18 6.8227 6.4452 BF 1.9998 1.9998 [Lens group data] Group Starting surface Focal length G1 1 -51.30 G2 10 16.18 G3 17 -33.44 G4 19 51.50 G1a 1 58.68 G1b 3 -17.36 G1c 7 89.35

Example

[0127] FIG. 21 is a lens configuration diagram of the inner focus optical system according to Embodiment 5 of the present invention.

[0128] The lens configuration of the inner focus optical system in FIG. 21 is composed of a first lens group G1 with a negative refractive power, a second lens group G2 with a positive refractive power, a third lens group G3 with a negative refractive power, and a fourth lens group G4 with a positive refractive power, in order from the object side to the image side.

[0129] The first lens group G1 is composed of a first a lens group G1a consisting of a positive meniscus lens with a convex surface facing the object side, a negative meniscus lens with a convex surface facing the object side, a first b lens group G1b consisting of a negative meniscus lens with a convex surface facing the object side, and a first c lens group G1c consisting of a positive meniscus lens with a convex surface facing the object side, in order from the object side to the image side.

[0130] The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

[0131] The second lens group G2 is composed of a cemented lens of a biconcave lens and a biconvex lens, a biconvex lens with both surfaces being aspherical, and a biconvex lens.

[0132] The third lens group G3 is composed of a negative meniscus lens with both surfaces being aspherical and the convex surface facing the object side, and focusing from an infinite object to a close-distance object is performed by moving the third lens group G3 toward the image side along the optical axis.

[0133] The fourth lens group G4 is composed of a positive meniscus lens with the convex surface facing the object side and a negative meniscus lens with the surface on the object side being aspherical and the convex surface facing the object side.

[0134] The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

[0135] Subsequently, the specifications of the inner focus optical system according to Example 5 are shown below.

[0136] Numerical Example 5 Unit: mm [Surface Data] Surface number r d nd vd Object plane ∞ (d0) 1 25.0945 2.6732 1.92286 20.88 2 31.2107 0.5000 3 23.6550 1.0000 1.59282 68.62 4 12.4474 4.5097 5 35.6606 1.0000 1.72916 54.67 6 17.2422 3.2231 7 61.4837 1.7140 1.91082 35.25 8 444.3886 9.0599 9 (Aperture) ∞ 3.7710 10 -32.9166 0.8000 1.85451 25.15 11 25.3205 6.0190 1.91082 35.25 12 -67.3367 1.0000 13* 100.0000 4.5344 1.69350 53.20 14* -28.6766 0.1500 15 60.0000 6.8742 1.59282 68.62 16 -27.9212 (d16) 17* 1000.0000 1.0052 1.68948 31.02 18* 21.9365 (d18) 19 25.0000 3.4227 1.90366 31.31 20 87.0749 0.1500 21* 18.1303 1.1000 1.68948 31.02 22 14.0000 14.7133 23 ∞ 4.1400 1.51633 64.14 24 ∞ (BF) Image plane ∞ [Aspherical data] Surface 13, Surface 14, Surface 17, Surface 18, Surface 21 K 0.00000 0.00000 0.00000 0.00000 0.00000 A4 -1.26177E-05 1.91343E-05 1.03854E-04 1.02563E-04 -6.80931E-06 A6 -1.32191E-07 -8.96820E-08 -8.04967E-07 -4.73547E-07 3.26123E-07 A8 1.49482E-09 8.27066E-10 3.07311E-09 1.66901E-10 -2.37833E-09 A10 -4.95682E-12 -1.36110E-12 -4.99188E-12 5.47673E-12 9.41390E-12 A12 5.36501E-15 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00 [Various data] INF Focal length 20.30 F-number 1.44 Full angle of view 2ω 60.31 Image height Y 11.15 Overall lens length 80.00 [Variable interval data] INF Magnification 0.025 d0 ∞ 792.9207 d16 2.0000 2.3414 d18 4.6409 4.2995 BF 1.9992 1.9992 [Lens group data] Group Starting surface Focal length G1 1 -52.54 G2 10 17.88 G3 17 -32.54 G4 19 55.62 G1a 1 114.70 G1b 3 -22.00 G1c 7 78.18

Example

[0137] FIG. 26 is a lens configuration diagram of the inner focus optical system according to Example 6 of the present invention.

[0138] The lens configuration of the inner focus optical system in FIG. 26 is composed of, in order from the object side to the image side, a first lens group G1 with a negative refractive power, a second lens group G2 with a positive refractive power, a third lens group G3 with a negative refractive power, and a fourth lens group G4 with a positive refractive power.

[0139] The first lens group G1 is composed of, in order from the object side to the image side, a first a lens group G1a consisting of a positive meniscus lens with a convex surface facing the object side, a first b lens group G1b consisting of a negative meniscus lens with a convex surface facing the object side and a biconcave lens, and a first c lens group G1c consisting of a biconvex lens.

[0140] The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

[0141] The second lens group G2 is composed of a biconcave lens, a cemented lens of a biconvex lens with an aspherical image-side surface, a biconvex lens, and a biconvex lens.

[0142] The third lens group G3 is composed of a negative meniscus lens with its convex surface facing the object side, and focusing from an infinite object to a near-distance object is performed by moving the third lens group G3 along the optical axis toward the image side.

[0143] The fourth lens group G4 is composed of a biconvex lens with both surfaces being aspherical and a negative meniscus lens with its convex surface facing the object side.

[0144] The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

[0145] Subsequently, the specifications of the inner focus optical system according to Example 6 are shown below.

[0146] Numerical Example 6 Unit: mm [Surface Data] Surface No. r d nd vd Object plane ∞ (d0) 1 64.0087 2.3222 2.05090 26.94 2 123.1071 0.5000 3 24.2785 1.0000 1.43700 95.10 4 12.3725 8.0358 5 -99.3978 0.8000 1.43700 95.10 6 20.5994 3.3032 7 86.2072 2.4280 1.90043 37.37 8 -89.3998 4.6764 9 (Aperture) ∞ 4.1026 10 -26.1617 2.4937 1.77047 29.74 11 28.7151 5.2598 1.76450 49.10 12* -44.2236 0.2500 13 500.0000 6.1832 1.55032 75.50 14 -21.7044 0.2500 15 38.4579 5.5320 1.59282 68.62 16 -39.2702 (d16) 17 74.8526 0.8000 1.65412 39.68 18 16.3510 (d18) 19* 27.7458 4.8915 1.80610 40.73 20* -90.0000 0.1500 21 33.4269 0.8000 1.61340 44.27 22 15.9455 14.3265 23 ∞ 4.1400 1.51633 64.14 24 ∞ (BF) Image plane ∞ [Aspherical data] Surface 12, Surface 19, Surface 20 K 0.00000 0.00000 0.00000 A4 3.16844E-05 1.59164E-05 2.04361E-05 A6 7.13515E-09 -3.62309E-09 -1.39412E-07 A8 7.39625E-12 2.26207E-10 1.82716E-09 A10 -8.28824E-13 1.35657E-12 -8.52823E-12 A12 2.78460E-15 -8.15502E-15 1.11999E-14 [Various data] INF Focal length 20.27 F number 1.43 Overall picture angle 2ω 58.16 Image height Y 11.15 Overall lens length 80.60 [Variable interval data] INF shooting magnification 0.025 d0 ∞ 791.5969 d16 1.8800 2.2335 d18 4.4785 4.1250 BF 2.0000 1.9999 [Lens group data] Group Starting surface Focal length G1 1 -92.19 G2 10 18.46 G3 17 -32.16 G4 19 50.21 G1a 1 124.37 G1b 3 -21.79 G1c 7 49.06

[0147] In addition, a list of corresponding values of the conditional expressions in each of these examples is shown. [Corresponding values of conditional expressions] Conditional expression Example 1 Example 2 Example 3 (1) f / f1 -0.26 -0.26 -0.32 (2) f / f2 1.10 1.27 1.21 (3) f / f3 -0.59 -0.78 -0.62 (4) f / f4 0.39 0.45 0.45 (5) f / f1b -0.88 -0.97 -1.24 (6) f / f1c 0.37 0.33 0.32 (7) M4 0.54 0.58 0.56 (8) |(M4^2×(1 - M3^2)| 1.40 1.89 1.33 (9) D / Y 5.36 5.30 4.94 (10) VdG1b 88.35 95.10 60.39 Conditional Examples 4, 5, 6 (1) f / f1 -0.40 -0.39 -0.22 (2) f / f2 1.25 1.14 1.10 (3) f / f3 -0.61 -0.62 -0.63 (4) f / f4 0.39 0.36 0.40 (5) f / f1b -1.17 -0.92 -0.93 (6) f / f1c 0.23 0.26 0.41 (7) M4 0.64 0.54 0.51 (8) |(M4^2×(1 - M3^2)| 1.35 1.49 1.44 (9) D / Y 5.03 5.05 5.16 (10) VdG1b 60.39 61.65 95.10

Explanation of Symbols

[0148] G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group G1a First a lens group G1b First b lens group G1c First c lens group S Aperture stop FL Optical filter I Image plane

Claims

1. From the object side to the image side in order, it consists of a first lens group G1 with negative refractive power, a diaphragm S, a second lens group G2 with positive refractive power, a third lens group G3 with negative refractive power, and a fourth lens group G4 with positive refractive power. The first lens group G1 consists of a first a lens group G1a composed of a positive single lens, a first b lens group G1b composed of two negative lenses, and a first c lens group G1c composed of a positive single lens in order from the object side to the image side. When focusing from an infinite object side to a near-distance object side, the third lens group G3 moves toward the image side, and it is characterized by an inner focus optical system that satisfies the following conditions. (1) -0.59 < f / f1 < -0.11 However, f: Focal length in the infinite focus state of the entire system f1: Focal length of the first lens group G1

2. The inner focus optical system according to Claim 1, characterized by satisfying the following conditions. (2) 0.55 < f / f2 < 2.55 (3) -1.56 < f / f3 < -0.29 (4) 0.18 < f / f4 < 0.90 (5) -2.48 < f / f1b < -0.44 (6) 0.11 < f / f1c < 0.83 However, f2: Focal length of the second lens group G2 f3: Focal length of the third lens group G3 f4: Focal length of the fourth lens group G4 f1b: Focal length of the first b lens group G1b f1c: Focal length of the first c lens group G1c

3. The inner focus optical system according to Claim 1 or 2, characterized by satisfying the following conditions. (7) 0.25 < M4 < 1.0 However, M4: Magnification burden of the fourth lens group when the object distance is infinite

4. The inner focus optical system according to any one of Claims 1 to 3, characterized by satisfying the following conditions. (8) 0.67 < |(M4^2 × (1 - M3^2))| < 3.78 However, M3: Magnification burden of the third lens group when the object distance is infinite M4: Magnification burden of the fourth lens group when the object distance is infinite

5. The inner focus optical system according to any one of Claims 1 to 4, characterized in that the third lens group G3 with negative refractive power consists of a single lens.

6. The inner focus optical system according to any one of Claims 1 to 5, characterized by satisfying the following conditions. (9) 2.47 < D / Y < 10.72 However, D: Length from the diaphragm to the image plane Y: Maximum image height

7. The inner focus optical system according to any one of Claims 1 to 6, characterized by satisfying the following conditions. (10) 55 < VdG1b However, VdG1b: Abbe number of the first lens group G1b

Images