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 comprises, in order from the object side to the image side, a first lens group G1 consisting of a single lens having negative refractive power, an aperture stop S, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive or negative refractive power, and is configured such that the third lens group G3 moves toward the object side when shifting focus from an object at infinity to an object at a short distance.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical system suitable for photographic lenses used in imaging devices such as still cameras and video cameras, and relates to an inner focus optical system that employs an inner focus method suitable for autofocus cameras, has a small rate of change in image height when the focus lens group is subjected to slight vibration (wobbling) along the optical axis, has a bright F-number of 1.4, and has an angle of view equivalent to 40 mm when converted into a 35 mm focal length. [Background technology]

[0002] Conventionally, wide-angle lenses used in photo cameras and still video cameras have been of the retrofocus type, in order to ensure a certain level of back focus for use in single-lens reflex systems that employ a mirror-up mechanism.

[0003] On the other hand, mirrorless cameras are often used for video shooting, so they often use an inner focus system for their autofocus, which constantly determines the focus drive direction by continuously vibrating (wobbling) the focus lens group slightly along the optical axis. In this case, if the rate of change in image height during wobbling is large, the viewer will notice the change in magnification of the subject on the screen and find it annoying, so a focus system that has a small rate of change in image height in response to focus changes is required.

[0004] In response to such demands, Patent Document 1 discloses a large-aperture lens that consists of, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power, with an aperture diaphragm disposed between the first lens group G1 and the second lens group G2, and focusing performed by moving the second lens group G2 toward the image plane side. By satisfying certain conditions, the lens discloses a high-performance large-aperture lens that, while having a simple configuration, reduces the weight of the focus lens group to accommodate autofocus during video shooting, has little aberration fluctuation due to focusing, and is adaptable to brightnesses of approximately an open F-number of 1.4 that employs an inner focus method.

[0005] Patent Document 2 discloses an imaging optical system with an angle of view of about 40 to 60°, which is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power, wherein when focusing from an object at infinity to an object at a close distance, 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 an image plane I, the first lens group G1 includes an aperture S and is composed of a predetermined lens group, and the third lens group G3 is composed of a predetermined lens group, and by satisfying a predetermined conditional expression, a short distance between the imaging optical system and the image sensor is achieved, thereby realizing a compact size, a small F-number, a suppressible light exit angle, and various aberrations are well corrected from infinity to close distance shooting. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-3324 A [Patent Document 2] JP 2015-75501 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the lens system disclosed in Patent Document 1, the focus lens group and the aperture are adjacent to each other, and therefore the rate of change in image height is large when the autofocus focus lens group is subjected to slight vibrations (wobbling) along the optical axis during video shooting, causing the viewer to perceive the change in magnification of the subject displayed on the screen and find this annoying.

[0008] Furthermore, in Patent Document 2, the focus lens group is composed of three lenses including a cemented lens, and therefore the weight of the focus lens group is not sufficiently reduced in order to perform autofocusing while subjecting the lens to minute vibrations.

[0009] Therefore, the present invention provides an inner focus optical system having a lightweight focus lens group, a small rate of change in image height when the focus lens group is subjected to slight vibration (wobbling) along the optical axis, a bright F-number of 1.4, and an angle of view equivalent to 40 mm in 35 mm format focal length, by the means described below. [Means for solving the problem]

[0010] In order to solve the above problems, the inner focus optical system of the first invention comprises, in order from the object side to the image side, a first lens group G1 consisting of a negative single lens, an aperture stop S, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a positive or negative refractive power. When focusing from the infinity object side to the close object side, the third lens group G3 moves toward the object side. and is characterized by satisfying the following conditions: do. (2) -0.55≦f2 / f1<-0.24 however, f1: focal length of the first lens group G1 f2: focal length of the second lens group G2

[0011] The inner focus optical system of the second aspect of the present invention is characterized in that it satisfies the following conditions. (1) -0.7 <f / f1<-0.14 (3) 0.15 <f / f3<0.76 (4) -0.2 <f / f4<0.1 however, f: focal length when the entire system is focused at infinity f1: focal length of the first lens group G1 f3: focal length of the third lens group G3 f4: Focal length of the fourth lens group G4

[0012] The inner focus optical system according to the third aspect of the present invention is characterized in that it satisfies the following conditions. (5) 0.7 <M4<1.0 however, M4: Magnification load of the fourth lens group G4 when focusing on an object at infinity

[0013] The inner focus optical system according to a fourth aspect of the present invention is characterized in that it satisfies the following conditions. (6) 0.25<(M4^2×(1-M3^2))<1.5 however, M3: Magnification load of the third lens group G3 when focusing on an object at infinity M4: Magnification load of the fourth lens group G4 when focusing on an object at infinity

[0014] The inner focus optical system according to the fifth aspect of the present invention is characterized in that it satisfies the following conditions. (7)60 <VdG1 however, VdG1: Abbe number of the first lens group G1

[0015] The inner focus optical system according to a sixth aspect of the present invention is characterized in that the third lens group G3 having positive refractive power is made up of a single lens.

[0016] The inner focus optical system according to the seventh aspect of the present invention is characterized in that it satisfies the following conditions: (8)2.5 <D / Y<10.4 however, D: Length from aperture stop S to image plane Y: Maximum image height Effect of the Invention

[0017] The present invention makes it possible to provide an inner focus optical system which employs an inner focus method suitable for autofocus cameras, has a small rate of change in image height when the focus lens group is subjected to slight vibration (wobbling) along the optical axis, has a bright F-number of 1.4, and has an angle of view equivalent to 40 mm when converted into a 35 mm focal length. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a lens configuration diagram of the inner focus optical system according to the first embodiment of the present invention at an infinite shooting distance. [Diagram 2] 5A to 5C are longitudinal aberration diagrams at an infinite shooting distance in Example 1 of the present invention. [Diagram 3] 5A to 5C are longitudinal aberration diagrams at a magnification of 0.025 in the first embodiment of the present invention. [Figure 4] 4A to 4C are diagrams showing lateral aberration at an infinite shooting distance in Example 1 of the present invention. [Diagram 5] 4A to 4C are lateral aberration diagrams at a magnification of 0.025 in the first embodiment of the present invention. [Figure 6] FIG. 11 is a lens configuration diagram of an inner focus optical system according to a second embodiment of the present invention at an infinite shooting distance. [Figure 7] 6A to 6C are longitudinal aberration diagrams at an infinite shooting distance in Example 2 of the present invention. [Figure 8] 6A to 6C are longitudinal aberration diagrams at a magnification of 0.025 in Example 2 of the present invention. [Figure 9] 4A to 4C are diagrams showing lateral aberration at an infinite shooting distance in Example 2 of the present invention. [Figure 10] 4A to 4C are lateral aberration diagrams at a magnification of 0.025 in Example 2 of the present invention. [Figure 11] FIG. 11 is a lens configuration diagram of an inner focus optical system according to a third embodiment of the present invention at an infinite shooting distance. [Figure 12] 11A to 11C are longitudinal aberration diagrams at an infinite shooting distance in Example 3 of the present invention. [Figure 13] 11A to 11C are longitudinal aberration diagrams at a magnification of 0.025 in Example 3 of the present invention. [Figure 14] 7A to 7C are diagrams showing lateral aberration at an infinite shooting distance in Example 3 of the present invention. [Figure 15] 7A to 7C are lateral aberration diagrams at a magnification of 0.025 in Example 3 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0020] As can be seen from the lens configuration diagrams shown in Figures 1, 6 and 11, the inner focus optical system of the present invention consists, in order from the object side to the image side, of 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 positive refractive power, and a fourth lens group G4 with positive or negative refractive power, and when focusing from the infinity object side to the close object side, the third lens group G3 moves toward the object side.

[0021] The reason why the above configuration is necessary is as follows: By making the inclination angle of the off-axis chief ray incident on the first lens surface at a large angle with respect to the optical axis gentler by the first lens group G1 having negative refractive power and exiting the lens surface, and by making it even gentler by the second lens group G2 having positive refractive power, it is possible to make the inclination angle of the off-axis chief ray incident on the third lens group G3, which is the focus lens group, gentler, which contributes to reducing the rate of change of image height.

[0022] In addition, as the incidence angle to the image sensor increases, shading becomes an issue, and therefore an optical system that reduces the exit angle of off-axis light beams is required. As described above, since the angle of the off-axis chief ray incident on the focus lens group with respect to the optical axis is small, it is possible to reduce the incidence angle of the off-axis chief ray reaching the image sensor without increasing the positive refractive power of the focus lens group. Furthermore, if the refractive power of the focus lens group is small, the lens group becomes lighter, which makes the focus lens group more susceptible to micro-vibrations (wobbling).

[0023] Furthermore, by disposing a lens group with positive refractive power between the diaphragm and the focus lens group, the image of the diaphragm as seen by the focus lens group is projected far away, making it possible to reduce the rate of change in image height.

[0024] Furthermore, by arranging the fourth lens group G4 on the image side of the focus lens group, it becomes possible to effectively correct residual aberration up to the focus lens group.

[0025] As a result, it is possible to provide an inner focus optical system that has a small rate of change in image height when the focus lens group is subjected to slight vibrations (wobbling) along the optical axis, and also has an angle of view equivalent to 40 mm in 35 mm format focal length.

[0026] Furthermore, it is preferable that the inner focus optical system of this embodiment satisfies the following conditional expression. (1) -0.7 <f / f1<-0.14 (2)-1.1 <f2 / f1<-0.24 (3) 0.15 <f / f3<0.76 (4) -0.2 <f / f4<0.1 however, f: focal length when the entire system is focused at infinity 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

[0027] In conditional formula (1), by appropriately defining the ratio of the focal length of the first lens group G1 to that of the entire system, it is possible to reduce the angle of incidence of light rays at the peripheral angle of view and transfer the light rays to the subsequent optical system.

[0028] When the negative refractive power of the first lens group G1 becomes large beyond the lower limit of conditional formula (1), the curvature of the concave surface in the first lens group G1 becomes even larger, which causes positive spherical aberration. In addition, the angle of incidence and the height of the axial ray on the second lens group G2 become large, which causes high-order aberration and makes it difficult to correct the aberration. In addition, the back focus becomes long, which increases the overall length of the optical system.

[0029] On the other hand, when the upper limit of conditional formula (1) is exceeded and the negative refractive power of the first lens group G1 becomes small, the inclination angle of the lower ray passing through the aperture stop S is not alleviated, so the angle of incidence of the lower ray incident on the subsequent lens group becomes large, making it difficult to correct coma flare of the lower ray.

[0030] Incidentally, by limiting the lower limit of condition (1) to -0.5 and the upper limit to -0.2, the above-mentioned effect can be ensured.

[0031] In conditional expression (2), by appropriately defining the ratio of the focal lengths of the second lens group G2 and the first lens group G1, the maximum angle of view of the peripheral field of view can be maintained while achieving a large aperture. comparison This becomes possible.

[0032] If the lower limit of conditional expression (2) is exceeded and the positive refractive power of the second lens group G2 becomes relatively small or the negative refractive power of the first lens group G1 becomes large, the overall refractive power cannot be secured unless the positive refractive power of the third lens group G3, which is the focus lens group, is increased, making it difficult to simultaneously correct the fluctuations in spherical aberration and astigmatism during focusing.

[0033] On the other hand, if the upper limit of conditional expression (2) is exceeded and the positive refractive power of the second lens group G2 becomes relatively large or the negative refractive power of the first lens group G1 becomes small, comparison It becomes difficult to correct spherical aberration and coma when the

[0034] Incidentally, with regard to condition (2), it is preferable to limit the lower limit to −0.85 and the upper limit to −0.32, so that the above-mentioned effect can be achieved more reliably.

[0035] In condition (3), by appropriately defining the ratio of the focal length of the third lens group G3, which is the focus lens group, to the focal length of the entire system when focusing at infinity, it is possible to suppress aberration fluctuations during focusing.

[0036] If the lower limit of condition (3) is exceeded and the positive refractive power of the third lens group becomes relatively small, the amount of movement of the third lens group G3 during focusing becomes large, and the overall length of the optical system becomes large. Also, the amount of amplitude during wobbling must be increased, which is undesirable since it places a load on the actuator.

[0037] On the other hand, if the upper limit of conditional expression (3) is exceeded and the positive refractive power of the third lens group G3 becomes relatively large, the amount of movement of the third lens group G3 during focusing becomes small, which is advantageous in terms of space, but it becomes difficult to simultaneously correct fluctuations in spherical aberration and astigmatism during focusing.

[0038] Incidentally, with regard to condition (3), it is preferable to limit the lower limit to 0.2 and the upper limit to 0.57, so that the above-mentioned effect can be obtained more reliably.

[0039] Condition (4) appropriately defines the ratio of the focal length of the fourth lens group G4 to that of the entire system, thereby making it possible to correct residual aberration up to the focus lens group and improve the performance of the entire system. In order to reduce the residual aberration of the fourth lens group G4 itself, it is necessary to weaken the refractive power of the fourth lens group G4 itself.

[0040] If the lower limit of conditional expression (4) is exceeded and the negative refractive power of the fourth lens group G4 becomes large, the imaging magnification of the fourth lens group G4 becomes a magnification system, which doubles the residual image aberration up to the focus lens group, making it difficult to achieve high performance.

[0041] On the other hand, if the upper limit of conditional expression (4) is exceeded and the positive refractive power of the fourth lens group G4 becomes large, the imaging magnification of the fourth lens group G4 becomes a reduction system, and the overall system becomes large, which is not preferable.

[0042] Incidentally, with regard to condition (4), it is preferable to limit the lower limit to −0.15 and the upper limit to 0.07, so that the above-mentioned effect can be achieved more reliably.

[0043] In order to reduce residual aberration in the fourth lens group itself, the lenses constituting the fourth lens group G4 need to be one positive lens and one negative lens.

[0044] Further, the present invention Inner focus optical system In this case, it is desirable to satisfy the following conditional expression. (5) 0.7 <M4<1.0 however, M4: Magnification load of the fourth lens group G4 when focusing on an object at infinity

[0045] Condition (5) defines the imaging magnification of the fourth lens group G4, which makes it possible to improve the performance of the entire system without amplifying the residual aberration up to the focus lens group.

[0046] If the lower limit of condition (5) is exceeded and the imaging magnification of the fourth lens group G4 becomes small, the residual aberration up to the focus group is reduced, but the overall system becomes large, which is undesirable.

[0047] On the other hand, if the upper limit of conditional expression (5) is exceeded and the imaging magnification of the fourth lens group G4 exceeds 1, the residual aberration up to the focus lens group increases, making it difficult to correct the aberration.

[0048] Incidentally, by setting the lower limit of condition (5) to 0.8, the above-mentioned effect can be ensured more reliably.

[0049] Further, the present invention Inner focus optical system In this case, it is desirable to satisfy the following conditional expression. (6) 0.25<(M4^2×(1-M3^2))<1.5 however, M3: Magnification load of the third lens group G3 when focusing on an object at infinity M4: Magnification load of the fourth lens group G4 when focusing on an object at infinity

[0050] Condition (6) defines the sensitivity of the imaging plane when the third lens group G3 moves during focusing. By appropriately defining this value, it becomes possible to drive and control the focus lens group with high precision within the focusing range during autofocus.

[0051] If the lower limit of condition (6) is exceeded and the sensitivity of the imaging surface when it moves during focusing decreases, the amount of movement of the focus lens group increases, causing greater fluctuations in the chief ray height of the focus lens group due to wobbling, weakening the effect of suppressing image height fluctuations, and making it difficult to suppress image height fluctuations due to wobbling.

[0052] On the other hand, if the upper limit of conditional expression (6) is exceeded and the sensitivity of the imaging surface when moved during focusing increases, the amount of movement of the focus lens group becomes small, so that even small movements of the focus lens group cause the imaging surface to move significantly, making it difficult to control the driving of the third lens group G3, which is the focus lens group, within the focusing range during autofocus.

[0053] Incidentally, with regard to condition (6), it is preferable to limit the lower limit to 0.35 or even 0.42 and the upper limit to 1.1 or even 0.95, in order to ensure the above-mentioned effect.

[0054] Further, the present invention Inner focus optical system In this case, it is desirable to satisfy the following conditional expression. (7)60 <VdG1 however, VdG1: Abbe number of the first lens group G1

[0055] Condition (7) defines the Abbe number of the first lens group G1 in order to improve performance.

[0056] If the lower limit of condition (7) is exceeded and the Abbe number of the first lens group G1 becomes small, lateral chromatic aberration worsens and it becomes difficult to correct this in the entire lens system.

[0057] Incidentally, by setting the lower limit of the above-mentioned conditional expression (7) to 65.0, the above-mentioned effect can be achieved more reliably.

[0058] Furthermore, in the inner focus optical system of the present invention, it is preferable that the third lens group G3 having a positive refractive power is composed of a single lens, which allows the focus group to be made lighter, and the actuator for driving the focus lens to be made smaller, thereby enabling a reduction in the product size.

[0059] Furthermore, the present invention Inner focus optical system In this case, it is desirable to satisfy the following conditional expression. (8)2.5 <D / Y<10.4 however, D: Length from aperture stop S to image plane Y: Maximum image height

[0060] Condition (8) makes it possible to suppress fluctuations in image height due to wobbling by appropriately defining the ratio of the length from the aperture stop S to the image plane to the maximum image height.

[0061] When the lower limit of condition (8) is exceeded and the ratio of the length from the aperture stop S to the image plane to the maximum image height becomes small, the angle of incidence to the off-axial image plane becomes large and the fluctuation in the chief ray height of the focus lens group during wobbling becomes large, making it difficult to suppress the fluctuation in image height during wobbling.

[0062] On the other hand, if the upper limit of condition (8) is exceeded and the ratio of the length from the aperture stop S to the image plane to the maximum image height becomes large, the overall optical system becomes large, which is undesirable.

[0063] Incidentally, by restricting the lower limit of condition (8) to 3.3 and the upper limit to 7.8, the above-mentioned effect can be ensured more reliably.

[0064] The inner focus optical system of the present invention is more effective when it has the following configuration.

[0065] In the inner focus optical system of the present invention, the third lens group G3 is composed of a single lens, but by achromatizing the focus lens group with a cemented lens or a diffractive optical surface, it is also possible to suppress fluctuations in chromatic aberration caused by the movement of the focus lens group during focusing.

[0066] Next, numerical examples of the inner focus optical system of the present invention will be described.

[0067] In [Surface Data], the surface number is the lens surface or aperture stop number 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 for the d-line (wavelength λ=587.56 nm), and νd is the Abbe number for the d-line. Also, BF stands for back focus.

[0068] For surfaces with numbers (apertures), the radius of curvature for the plane or aperture diaphragm is entered as ∞ (infinity). Also, the refractive index of air, n=1.0000, is omitted.

[0069] [Aspheric Data] shows the coefficient values ​​that give the aspheric shape of lens surfaces marked with an * in [Surface Data]. The aspheric shape is expressed by the following formula, where y is the displacement perpendicular to the optical axis, z is the displacement (sag) from the intersection of the aspheric surface and the optical axis in the direction of the optical axis, K is the Conic coefficient, and A4, A6, A8, and A10 are the 4th, 6th, 8th, and 10th order aspheric coefficients, respectively. TIFF0007603981000001.tif37170

[0070] [Various data] shows values ​​such as focal length.

[0071] [Variable Distance Data] shows the variable distance and BF (back focus) values ​​for each shooting distance state or each shooting magnification state.

[0072] [Lens Group Data] shows the surface number of each lens group closest to the object and the composite focal length of the entire group. Note that in all the values ​​of the following specifications, the focal length f, radius of curvature r, lens surface interval d, and other length units are in millimeters (mm) unless otherwise specified, but this is not a limitation because the optical system can obtain the same optical performance in proportional magnification and proportional reduction.

[0073] 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 construction diagrams shown in Figures 1, 6, and 11, S represents the aperture stop, I represents the image plane, and the dashed line passing through the center represents the optical axis.

[0074] In the following description, the lens configuration will be described in order from the object side to the image side. EXAMPLES

[0075] FIG. 1 is a lens configuration diagram of an inner focus optical system according to a first embodiment of the present invention.

[0076] The lens configuration of the inner focus optical system in FIG. 1 consists, from the object side to the image side, of a first lens group G1 consisting of a negative single lens, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4.

[0077] The first lens group G1 is composed of a negative meniscus lens whose image-side surface is aspheric and whose convex surface faces the object side.

[0078] The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

[0079] The second lens group G2 is composed of a cemented lens consisting of a biconcave lens and a biconvex lens with an aspheric image-side surface, a biconvex lens with an aspheric image-side surface, and a negative meniscus lens with a convex surface facing the object side.

[0080] The third lens group G3 is composed of a positive meniscus lens with an aspheric surface facing the object side and a convex surface facing the object side, and focusing from an object at infinity to a close object is performed by moving the third lens group G3 toward the object side along the optical axis.

[0081] The fourth lens group G4 is composed of a biconvex lens with an aspheric surface on the image side and a negative meniscus lens with a convex surface facing the object side.

[0082] The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

[0083] Next, the specifications of the inner focus optical system according to the first embodiment are shown below.

[0084] Numerical Example 1 Unit: mm [Face data] Surface number rd nd vd Object surface ∞ (d0) 1 32.0388 0.8000 1.43700 95.10 2* 14.6670 11.1597 3(Aperture) ∞ 4.5000 4 -17.0058 1.0000 1.69895 30.05 5 16.2489 8.4632 1.95375 32.32 6* -33.9676 0.1200 7 214.7544 8.0304 1.55032 75.50 8* -18.7360 0.1500 9 36.8096 0.8000 1.77047 29.74 10 22.9590 (d10) 11* 21.5733 2.9573 1.55032 75.50 12 45.5492 (d12) 13 27.7656 5.3439 1.55032 75.50 14* -26.7603 0.4000 15 112.5648 0.8000 1.62004 36.30 16 12.2002 10.0000 17 ∞ 4.1400 1.51633 64.14 18∞(BF) Image plane ∞ [Aspheric data] 2nd 6th 8th 11th K 0.00000 0.00000 0.00000 0.00000 A4 3.83637E-06 4.29774E-05 1.05048E-05 1.16709E-05 A6 2.91048E-08 2.69092E-08 4.45041E-08 0.00000E+00 A8 -2.87852E-10 4.62121E-10 -3.91584E-10 0.00000E+00 A10 1.68904E-13 -1.12868E-12 1.75222E-12 0.00000E+00 14 sides K 0.00000 A4 5.55756E-05 A6 -1.10645E-07 A8 3.69358E-10 A10 -3.18282E-13 [Various data] INF Focal length 20.88 F-number 1.44 Full angle of view 2ω 57.48 Image height Y 11.15 Lens total length 70.00 [Variable interval data] INF Magnification 0.025 d0∞825.6781 d10 4.8788 3.9918 d12 1.9000 2.7870 BF 4.5568 4.5618 [Lens group data] Group starting plane focal length G1 1 -62.78 G2 4 34.69 G3 11 71.35 G4 13 -701.15 EXAMPLES

[0085] FIG. 6 is a lens configuration diagram of an inner focus optical system according to a second embodiment of the present invention.

[0086] The lens configuration of the inner focus optical system in FIG. 6 is composed of, from the object side to the image side, a first lens group G1 with negative refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4.

[0087] The first lens group G1 is composed of a negative meniscus lens whose image-side surface is aspheric and whose convex surface faces the object side.

[0088] The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

[0089] The second lens group G2 is composed of a cemented lens of a biconcave lens and a biconvex lens with an aspheric image-side surface, a positive meniscus lens with an aspheric image-side surface facing its concave surface toward the object side, and a negative meniscus lens with a convex surface facing the object side.

[0090] The third lens group G3 is composed of a positive meniscus lens with an aspheric surface facing the object side and a convex surface facing the object side, and focusing from an object at infinity to a close object is performed by moving the third lens group G3 toward the object side along the optical axis.

[0091] The fourth lens group G4 is composed of a biconvex lens with an aspheric surface on the image side and a negative meniscus lens with a convex surface facing the object side.

[0092] The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

[0093] Next, the specifications of the inner focus optical system according to the second embodiment are shown below.

[0094] Numerical Example 2 Unit: mm [Face data] Surface number rd nd vd Object surface ∞ (d0) 1 22.4258 1.4245 1.43700 95.10 2* 12.9157 5.1771 3(Aperture) ∞ 4.5000 4 -12.9870 1.0000 1.68960 31.14 5 16.8324 8.1671 1.91082 35.25 6* -20.7231 0.1200 7 -80.0936 6.3211 1.55032 75.50 8* -18.7288 0.1500 9 53.6073 0.8000 1.77047 29.74 10 30.5674 (d10) 11* 23.2320 2.9192 1.55032 75.50 12 57.4623 (d12) 13 26.7089 5.7856 1.55032 75.50 14* -24.6480 0.4000 15 1315.4530 0.8000 1.64769 33.84 16 14.5756 10.0000 17 ∞ 4.1400 1.51633 64.14 18∞(BF) Image plane ∞ [Aspheric data] 2nd 6th 8th 11th K 0.00000 0.00000 0.00000 0.00000 A4 1.65699E-05 5.48007E-05 -1.00626E-05 1.17188E-05 A6 3.56775E-07 -6.03051E-08 2.08309E-07 2.55430E-09 A8 -7.94017E-09 1.21635E-09 -1.40273E-09 2.19035E-11 A10 7.67081E-11 -3.37417E-12 5.42867E-12 0.00000E+00 14 sides K 0.00000 A4 5.63707E-05 A6 -6.00693E-08 A8 1.72740E-10 A10 5.46529E-15 [Various data] INF Focal length 20.76 F-number 1.45 Full angle of view 2ω 61.00 Image height Y 11.15 Lens total length 62.00 [Variable interval data] INF Magnification 0.025 d0∞825.6781 d10 4.2658 3.2863 d12 1.9000 2.8795 BF 4.1299 4.1349 [Lens group data] Group starting plane focal length G1 1 -73.02 G2 4 36.30 G3 11 68.78 G4 13 439.93 EXAMPLES

[0095] FIG. 11 is a lens configuration diagram of an inner focus optical system according to a third embodiment of the present invention.

[0096] The lens configuration of the inner focus optical system in FIG. 11 is composed of, from the object side to the image side, a first lens group G1 with negative refractive power, a second lens group G2 with positive refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4.

[0097] The first lens group G1 is composed of a negative meniscus lens whose image-side surface is aspheric and whose convex surface faces the object side.

[0098] The aperture stop S is disposed between the first lens group G1 and the second lens group G2.

[0099] The second lens group G2 is composed of a cemented lens of a biconcave lens and a biconvex lens with an aspheric image-side surface, a positive meniscus lens with an aspheric image-side surface facing its concave surface toward the object side, and a negative meniscus lens with a convex surface facing the object side.

[0100] The third lens group G3 is composed of a positive meniscus lens with an aspheric surface facing the object side and a convex surface facing the object side, and focusing from an object at infinity to a close object is performed by moving the third lens group G3 toward the object side along the optical axis.

[0101] The fourth lens group G4 is composed of a biconvex lens with an aspheric surface on the image side and a negative meniscus lens with a convex surface facing the object side.

[0102] The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

[0103] Next, the specifications of the inner focus optical system according to the third embodiment are shown below.

[0104] Numerical Example 3 Unit: mm [Face data] Surface number rd nd vd Object surface ∞ (d0) 1 23.7655 0.8000 1.43700 95.10 2* 13.5093 6.2353 3(Aperture) ∞ 4.5000 4 -13.7458 1.0000 1.68960 31.14 5 16.3642 8.5116 1.91082 35.25 6* -20.5258 0.1200 7 -74.7209 6.1105 1.55032 75.50 8* -18.6497 0.1500 9 139.9599 0.8000 1.77047 29.74 10 43.7276 (d10) 11* 24.3786 3.3184 1.55032 75.50 12 119.4795 (d12) 13 34.4057 5.0848 1.55032 75.50 14* -24.7678 0.4000 15 140.4322 0.8000 1.64769 33.84 16 12.9754 10.0000 17 ∞ 4.1400 1.51633 64.14 18∞(BF) Image plane ∞ [Aspheric data] 2nd 6th 8th 11th K 0.00000 0.00000 0.00000 0.00000 A4 1.55178E-05 6.19958E-05 -6.48757E-06 1.98642E-05 A6 2.27973E-07 -9.43577E-08 2.61596E-07 -8.15556E-09 A8 -5.58737E-09 9.60232E-10 -1.49931E-09 -4.18352E-11 A10 5.04990E-11 -1.94064E-12 5.65937E-12 0.00000E+00 14 sides K 0.00000 A4 5.67495E-05 A6 -6.00693E-08 A8 1.72740E-10 A10 5.46529E-15 [Various data] INF Focal length 20.80 F-number 1.45 Full angle of view 2ω 59.22 Image height Y 11.15 Lens total length 62.00 [Variable interval data] INF Magnification 0.025 d0∞825.6781 d10 3.8351 3.1405 d12 1.9000 2.5946 BF 4.2944 4.2994 [Lens group data] Group starting plane focal length G1 1 -73.37 G2 4 35.14 G3 11 54.97 G4 13 -237.78

[0105] Also shown is a list of values ​​corresponding to the conditional expressions in each of these embodiments.

[0106] [Conditional expression corresponding value] Conditional Expression Example 1 Example 2 Example 3 (1) f / f1 -0.33 -0.28 -0.28 (2) f2 / f1 -0.55 -0.50 -0.48 (3) f / f3 0.29 0.30 0.38 (4) f / f4 -0.03 0.05 -0.09 (5) M4 0.92 0.85 0.98 (6) (M4^2×(1-M3^2)) 0.58 0.52 0.74 (7) VdG1 95.10 95.10 95.10 (8) D / Y 5.21 4.97 4.93 [Explanation of symbols]

[0107] G1 First lens group G2 2nd lens group G3 3rd lens group G4 4th lens group S aperture stop FL Optical Filter I image plane

Claims

1. An inner focus optical system comprising, in order from the object side to the image side, a first lens group G1 consisting of a negative single lens, an aperture stop S, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having positive or negative refractive power, wherein when focusing from the infinity object side to the close object side, the third lens group G3 moves toward the object side, and the following condition is satisfied: (2) -0.55≦f2 / f1<-0.24 however, f1: focal length of the first lens group G1 f2: focal length of the second lens group G2

2. 2. The inner focus optical system according to claim 1, wherein the following condition is satisfied: (1) -0.7<f / f1<-0.14 (3) 0.15<f / f3<0.76 (4) -0.2<f / f4<0.1 however, f: focal length when the entire system is focused at infinity f1: focal length of the first lens group G1 f3: focal length of the third lens group G3 f4: focal length of the fourth lens group G4

3. 3. The inner focus optical system according to claim 1, wherein the following condition is satisfied: (5) 0.7<M4<1.0 however, M4: Magnification load of the fourth lens group G4 when focusing on an object at infinity

4. 4. The inner focus optical system according to claim 1, wherein the following condition is satisfied: (6) 0.25<(M4^2×(1-M3^2))<1.5 however, M3: Magnification load of the third lens group G3 when focusing on an object at infinity M4: Magnification load of the fourth lens group G4 when focusing on an object at infinity

5. 5. The inner focus optical system according to claim 1, wherein the following condition is satisfied: (7) 60<VdG1 however, VdG1: Abbe number of the first lens group G1

6. 6. The inner focus optical system according to claim 1, wherein the third lens group G3 having a positive refractive power is composed of a single lens.

7. 7. The inner focus optical system according to claim 1, wherein the following condition is satisfied: (8) 2.5<D / Y<10.4 however, D: Length from aperture stop S to image plane Y: Maximum image height

Images