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, a 35 mm format equivalent focal length of approximately 80 mm, and about a medium telephoto angle of view.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 positive refractive power, 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, and is configured such that the second lens group G2 moves toward the object side and 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. An aperture stop S is located in the first lens group.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 system 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 of approximately 80 mm in 35 mm equivalent focal length, or a medium telephoto angle. [Background technology]

[0002] Shooting lenses with a medium telephoto angle of view tend to have a longer focal length than standard angle of view lenses, so the overall optical length tends to be longer. Also, because the angle of view is wider than that of super telephoto lenses, the telephoto ratio tends to be larger when attempting to correct aberrations related to the angle of view. Also, many users expect that shooting lenses with a medium telephoto angle of view can be used to create photographic expressions using bokeh, and large aperture lenses are often used. ratio However, a large-diameter photographic lens is desired. ratio However, when the size is increased, the entrance pupil becomes larger, making it difficult to correct spherical aberration, etc. The challenge is to achieve better performance while reducing the size.

[0003] Furthermore, mirrorless single-lens cameras, which have become popular in recent years, are also frequently used for video shooting, and so they often use an inner focus system for their autofocus, which constantly determines the focus drive direction by continuously vibrating the focus lens group slightly (wobbling) in the direction 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 displayed on the screen and find it distracting, so a focus system that has a small rate of change in image height in response to changes in focus is required.

[0004] In response to such demands, Patent Document 1 discloses a large-aperture lens that is composed 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 stop 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.By satisfying certain conditions, the lens has a simple configuration while reducing the weight of the focus lens to accommodate autofocusing during video shooting, while also exhibiting little aberration fluctuation due to focusing, and is adaptable to brightnesses up to an aperture value of approximately F1.4 using an inner focus system.

[0005] Patent Document 2 also discloses an inner focus optical system with an angle of view of approximately 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 close range, 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 stop S and is composed of a predetermined lens group, and the third lens group G3 is also composed of a predetermined lens group, and by satisfying predetermined conditional expressions, the distance between the inner focus optical system and the image sensor is short, thereby achieving compactness, a small F-number, a reduced light exit angle, and excellent correction of various aberrations from infinity to close range photography.

[0006] Patent Document 3 also discloses a lens system that includes, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, and that focuses by moving the second lens group along the optical axis.

[0007] Furthermore, Patent Document 4 discloses that the lens essentially consists of, in order from the object side, a first lens group having positive refractive power, an aperture stop, and a second lens group having positive refractive power, and that focusing is performed by moving multiple lenses in the second lens group or the entire second lens group G2 toward the object side. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-3324 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-75501 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-242690 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-141384 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the lens system disclosed in Patent Document 1, the focus lens group and the aperture are adjacent to each other, and therefore when the autofocus focus lens group is subjected to slight vibrations (wobbling) along the optical axis during video shooting, the rate of change in image height is large, which poses a problem in that the viewer becomes aware of the change in magnification of the subject displayed on the screen and finds it distracting.

[0010] In addition, in Patent Document 2, the FNO is about 1.8, so the amount of blur is small, and ratio Furthermore, since the focus lens group is made up of three lenses, including a cemented lens, it is possible to achieve a large aperture. ratio However, the weight of the focus lens group is not sufficiently reduced to perform autofocusing while generating minute vibrations.

[0011] In addition, in Patent Document 3, the FNO is about 1.8, so the amount of blur is small, and ratio The challenge is to

[0012] Furthermore, in Patent Document 4, the focus lens group is made up of a plurality of lenses, and therefore the weight of the focus lens group is not sufficiently reduced to perform autofocusing while causing minute vibrations (wobbling).

[0013] Therefore, the present invention provides an inner focus optical system that uses a lightweight focus lens group, has a small rate of change in image height when the focus lens group is subjected to slight vibrations (wobbling) along the optical axis, has a bright F-number of 1.4, and has a focal length of around 80 mm in 35 mm format equivalent, or an angle of view of a medium telephoto lens, by the means described below. [Means for solving the problem]

[0014] 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 having positive refractive power, 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, and when focusing from the infinity object side to the close object side, the second lens group G2 moves toward the object side and the third lens group G3 moves toward the image side, The first lens group G1 and the fourth lens group G4 are fixed relative to the image plane, The aperture stop S is located in the first lens group G1. , characterized by satisfying the following conditions: (2) 0.35 <f / f2<2.22 however, f: focal length when the entire system is focused at infinity f2: Focal length of the second lens group G2

[0015] The inner focus optical system of the second invention is characterized by satisfying the following conditions. (1) 0.12 <MR<1.70 (3)-2.55 <f / f3<-0.52 (4) 0.34 <f / f4<2.68 however, MR: Magnification burden of the composite system from the second lens group onwards when the object distance is infinity f: focal length when the entire system is focused at infinity f3: Focal length of the third lens group G3 f4: Focal length of the fourth lens group G4

[0016] The inner focus optical system of the third invention is characterized by satisfying the following conditions. (5) 0.15 <M4<1.0 however, M4: Magnification load of the fourth lens group G4 at the object distance infinity

[0017] The inner focus optical system of the fourth aspect of the present invention is characterized by satisfying the following conditions. (6)0.35<((M3×M4)^2×(1-M2^2))<2.18 (7)0.42<|(M4^2×(1-M3^2))|<2.10 however, M2: Magnification load of the second lens group G2 when the object distance is infinity M3: Magnification load of the third lens group G3 at the object distance infinity M4: Magnification load of the fourth lens group G4 at the object distance infinity

[0018] The inner focus optical system of the fifth invention is characterized in that the second lens group G2 with positive refractive power and the third lens group G3 with negative refractive power are each composed of a single lens.

[0019] The inner focus optical system of the sixth aspect of the invention is characterized by satisfying the following conditions: (8)2.03 <D / Y<9.98 however, D: Length from the aperture to the image plane Y: Maximum image height [Effects of the Invention]

[0020] The present invention makes it possible to provide an inner focus optical system that employs an inner focus system 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 a focal length of around 80 mm in 35 mm format, or a medium telephoto angle. [Brief explanation of the drawings]

[0021] [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. [Figure 2] FIG. 10 is a longitudinal aberration diagram at an infinite shooting distance in Example 1 of the present invention. [Figure 3] 4A to 4C are longitudinal aberration diagrams at a magnification of 0.025 in Example 1 of the present invention. [Figure 4] 4A to 4C are diagrams illustrating lateral aberration at an infinite shooting distance in Example 1 of the present invention. [Figure 5] 4A to 4C are diagrams showing lateral aberration at a magnification of 0.025 in Example 1 of the present invention. [Figure 6] FIG. 10 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] FIG. 10 is a longitudinal aberration diagram at an infinite shooting distance in Example 2 of the present invention. [Figure 8] 10A and 10B are longitudinal aberration diagrams at a magnification of 0.025 in Example 2 of the present invention. [Figure 9] 10A and 10B are diagrams illustrating lateral aberration at an infinite shooting distance in Example 2 of the present invention. [Figure 10] 10A to 10C are diagrams showing lateral aberration at a magnification of 0.025 in Example 2 of the present invention. [Figure 11] FIG. 10 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] 10A and 10B are longitudinal aberration diagrams at an infinite shooting distance in Example 3 of the present invention. [Figure 13] 10A and 10B are longitudinal aberration diagrams at a magnification of 0.025 in Example 3 of the present invention. [Figure 14] 10A to 10C are diagrams showing lateral aberration at an infinite shooting distance in Example 3 of the present invention. [Figure 15] 10A to 10C are diagrams showing lateral aberration at a magnification of 0.025 in Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The inner focus optical system of this embodiment will be described below. Note that the following description of the example is an example of the optical system of the present invention, and the present invention is not limited to this example within the scope of the gist of the present invention.

[0023] As can be seen from the lens configuration diagrams shown in FIGS. 1, 6, and 11, 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 positive refractive power, 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. When focusing from the infinity object side to the close object side, the second lens group G2 moves toward the object side, the third lens group G3 moves toward the image side, and an aperture stop S is located within the first lens group G1.

[0024] The reason why the above configuration is necessary is as follows. By arranging four groups of positive-positive-negative-positive in order from the object side, and when focusing from the infinity object side to the close object side, the second lens group G2 moves toward the object side and the third lens group G3 moves toward the image side, and by sharing the focusing action between the second lens group G2 and the third lens group G3, it is possible to suppress aberration fluctuations during focusing while suppressing an increase in the number of lenses constituting the focus lens group, which makes it possible to reduce the weight of the focus group, increase focusing speed, and even make the focus group vibrate slightly (wobble). In particular, with a large aperture where the effective diameter of the focus group is large and aberration fluctuations during focusing are large ratio In imaging lenses, the effect of reducing the weight of the focus group becomes significant.

[0025] Furthermore, it is possible to have fluctuations in field curvature and spherical aberration during focusing cancelled out by the second lens group G2 and the third lens group G3, or the first lens group G1 and the second lens group G2, making it possible to effectively correct aberrations while minimizing the number of lenses constituting the focus group.

[0026] Furthermore, by arranging a lens group on the image side of the focus lens group, it becomes possible to effectively correct residual aberrations up to the focus lens group.

[0027] Furthermore, by locating the diaphragm within the first lens group G1, it is possible to reduce the rate of change in image height when the focus lens group is subjected to slight vibration (wobbling) in the direction along the optical axis.

[0028] These features make it 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, a bright F-number of 1.4, and an angle of view equivalent to a focal length of around 80mm in 35mm format, or a medium telephoto angle.

[0029] Furthermore, it is preferable that the inner focus optical system of this embodiment satisfy the following conditional expression. (1) 0.12 <MR<1.70 (2) 0.35 <f / f2<2. 22 (3)-2.55 <f / f3<-0.52 (4) 0.34 <f / f4<2.68 however, MR: Magnification burden of the composite system from the second lens group onwards when the object distance is infinity f: focal length when the entire system is focused at infinity 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

[0030] In conditional expression (1), by appropriately defining the magnification load of the composite system from the second lens group G2 onwards when the object distance is at infinity, it is possible to suppress aberration fluctuations during focusing while also preventing the entire system from becoming large.

[0031] When the lower limit of conditional expression (1) is exceeded and the magnification of the composite system from the second lens group G2 onward at an object distance of infinity becomes small, the residual aberration of the first lens group G1 is reduced by the composite system from the second lens group G2 onward. However, the residual aberration of the composite system from the second lens group G2 onward must also be reduced to reduce the aberration of the entire system. Therefore, it is necessary to either reduce the refractive power of the second lens group G2 onward or increase the number of lenses in the second lens group G2 onward to improve aberration correction capability. In the present invention, the second lens group G2 and the third lens group G3 onward serve as focus lens groups. Therefore, if the refractive power of the second lens group G2 onward becomes small, the amount of movement of the second lens group G2 and the third lens group G3 required for focusing increases. This results in an insufficient air gap required for focusing. If an attempt is made to secure this space, the overall length of the optical system undesirably increases. Furthermore, increasing the number of lenses in the second lens group G2 onward makes it difficult to reduce the weight of the focus lens group.

[0032] On the other hand, if the upper limit of conditional expression (1) is exceeded and the magnification of the composite system from the second lens group G2 onwards increases when the object distance is at infinity, this is advantageous for making the entire system more compact, but the residual aberrations of the first lens group G1 will be magnified in the composite system from the second lens group G2 onwards, and in order to cancel these aberrations, it will be necessary to compensate in a way that causes residual aberrations in the composite system from the second lens group G2 onwards. In this case, it becomes difficult to suppress aberration fluctuations during focusing in the second and third lens groups G2 and G3, which are the focus lens groups.

[0033] It is to be noted that, with regard to conditional expression (1), it is desirable to limit the lower limit to 0.17 and the upper limit to 1.27, thereby making it possible to more reliably achieve the above-mentioned effect.

[0034] Conditional expression (2) makes it possible to suppress aberration fluctuations during focusing by appropriately defining the ratio between the focal length of the second lens group G2, which is the focus lens group, and the focal length of the entire system.

[0035] If the positive refractive power of the second lens group G2 becomes smaller by going below the lower limit of conditional expression (2), the amount of movement of the second lens group G2 during focusing increases, the overall length of the optical system increases, and the amplitude of wobbling must also increase, which is undesirable because it places a load on the actuator.

[0036] 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 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.

[0037] It should be noted that, with regard to conditional expression (2), it is desirable to set the lower limit to 0.46 and the upper limit to 2.22, thereby making it possible to ensure the above-mentioned effect.

[0038] In conditional expression (3), by appropriately defining the ratio between the focal length of the third lens group G3, which is the focus lens group, and the focal length of the entire system when focused at infinity, it is possible to suppress aberration fluctuations during focusing.

[0039] If the lower limit of conditional expression (3) is exceeded and the negative refractive power of the third lens group G3 becomes 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.

[0040] On the other hand, if the upper limit of conditional expression (3) is exceeded and the negative refractive power of the third lens group G3 becomes small, the amount of movement of the third lens group G3 during focusing increases, the overall length of the optical system increases, and the amplitude of wobbling must also increase, which is undesirable as it places a load on the actuator.

[0041] It should be noted that, with regard to conditional expression (3), it is desirable to limit the lower limit to -1.91 and the upper limit to -0.69, thereby making it possible to ensure the above-mentioned effect.

[0042] Conditional expression (4) appropriately defines the ratio of the focal lengths of the fourth lens group G4 and the entire system, thereby correcting residual aberrations up to the focus lens group and improving the performance of the entire system. In addition, to reduce residual aberrations in the fourth lens group G4 itself, it is necessary to weaken the refractive power of the fourth lens group G4 itself.

[0043] If the lower limit of conditional expression (4) is exceeded and the positive refractive power of the fourth lens group G4 becomes smaller, the imaging magnification of the fourth lens group G4 becomes larger, which reduces the effect of reducing afterimage aberration up to the focus lens group, making it difficult to achieve high performance.

[0044] 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 smaller, making it easier to correct aberrations, but this is not desirable as it increases the size of the entire system.

[0045] It should be noted that, with regard to conditional expression (4), it is desirable to set the lower limit to 0.45 and the upper limit to 2.01, thereby making it possible to ensure the above-mentioned effect.

[0046] Furthermore, it is desirable that the inner focus optical system of the present invention satisfy the following conditional expression. (5) 0.15 <M4<1.0 however, M4: Magnification load of the fourth lens group G4 at the object distance infinity

[0047] Condition (5) defines the imaging magnification of the fourth lens group G4. In the inner focus optical system of the present invention, by making the imaging magnification of the fourth lens group G4, which is the final lens group, a reduction system, it is possible to improve the performance of the entire system without amplifying the residual aberration up to the focus lens group.

[0048] 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.

[0049] 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.

[0050] It should be noted that, with regard to conditional expression (5), it is desirable to set the lower limit to 0.21 and the upper limit to 0.94, thereby making it possible to ensure the above-mentioned effect.

[0051] Furthermore, it is desirable that the inner focus optical system of the present invention satisfy the following conditional expression. (6)0.35<((M3×M4)^2×(1-M2^2))<2.18 (7)0.42<|(M4^2×(1-M3^2))|<2.10 however, M2: Magnification load of the second lens group G2 when the object distance is infinity M3: Magnification load of the third lens group G3 at the object distance infinity M4: Magnification load of the fourth lens group G4 at the object distance infinity

[0052] Conditional expressions (6) and (7) define the sensitivity of the imaging plane when the second lens group G2 and the third lens group G3 move during focusing. By appropriately defining these values, it becomes possible to precisely drive and control the focus lens group within the focusing range during autofocus.

[0053] If the lower limits of conditional expressions (6) and (7) are exceeded, and the sensitivity of the imaging surface when it moves during focusing decreases, the amount of movement of the focus lens group increases, which increases the fluctuation 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.

[0054] On the other hand, if the upper limits of conditional expressions (6) and (7) are exceeded and the sensitivity of the imaging plane when moved during focusing increases, the amount of movement of the focus lens group decreases, so that even a slight movement of the focus lens group will cause the imaging plane to move significantly, making it difficult to drive and control the second lens group G2 and the third lens group G3, which are the focus lens groups, within the focusing range during autofocus.

[0055] It should be noted that, with regard to conditional expression (6), it is desirable to set the lower limit to 0.47 and the upper limit to 1.63, thereby making it possible to ensure the above-mentioned effect.

[0056] Moreover, by limiting the lower limit of conditional expression (7) to 0.56 and the upper limit to 1.58, the above-mentioned effect can be more reliably achieved.

[0057] Furthermore, in the inner focus optical system of the present invention, it is desirable that the second lens group G2 with positive refractive power and the third lens group G3 with negative refractive power each consist of a single lens, which allows for a reduction in the weight of the focus group, the size of the focus drive actuator, and ultimately the size of the product.

[0058] Furthermore, it is desirable that the inner focus optical system of the present invention satisfy the following conditional expression. (8)2.03 <D / Y<9.98 however, D: Length from aperture stop S to image plane Y: Maximum image height

[0059] Condition (8) makes it possible to suppress fluctuations in image height during wobbling by appropriately defining the ratio between the length from the aperture stop S to the image plane and the maximum image height.

[0060] If the lower limit of conditional expression (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 increases, causing a large fluctuation in the height of the chief ray of light from the focus lens group during wobbling, making it difficult to suppress fluctuations in image height during wobbling.

[0061] On the other hand, if the upper limit of conditional expression (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.

[0062] It is to be noted that, with regard to conditional expression (8), it is desirable to set the lower limit to 2.70 and the upper limit to 7.48, thereby making it possible to ensure the above-mentioned effect.

[0063] The inner focus optical system of the present invention is more effective when it has the following configuration.

[0064] In the inner focus optical system of the present invention, the third lens group is composed of a single lens, but by making the focus lens group achromatic or giving it an aspherical effect using a cemented lens, a diffractive optical surface, or a metalens structure surface, it is also possible to suppress fluctuations in chromatic aberration, spherical aberration, coma, and astigmatism due to focus movement.

[0065] Furthermore, to reduce minute vibrations (wobbling) during focusing, only one of the second lens group G2 and the third lens group G3, or both, may be used.

[0066] Next, a lens configuration of an embodiment of the inner focus optical system of the present invention will be described. In the following description, the lens configuration will be described in order from the object side to the image side.

[0067] Furthermore, specific numerical data for each example will be shown.

[0068] 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 spacing between surfaces, nd is the refractive index for the d-line (wavelength 587.56 nm), and vd is the Abbe number for the d-line.

[0069] An asterisk (*) next to a surface number indicates that the lens surface is aspherical, and BF represents the back focal length.

[0070] The (diaphragm) next to the surface number indicates that an aperture diaphragm is located at that position. The radius of curvature for the plane or aperture diaphragm is marked as ∞ (infinity).

[0071] [Aspherical Data] shows the coefficient values ​​that give the aspherical shape of lens surfaces marked with an * in [Surface Data]. The shape of the aspherical surface is expressed by the following equation, where y is the displacement from the optical axis in a direction perpendicular to the optical axis, z is the displacement (sag) from the intersection of the aspherical surface and the optical axis in the direction of the optical axis, r is the radius of curvature of the reference sphere, K is the Conic coefficient, and A4, A6, A8, A10, and A12 are the aspherical coefficients of the 4th, 6th, 8th, 10th, and 12th orders, respectively.

[0072] TIFF0007766908000001.tif19147

[0073] [Various data] shows values ​​such as focal length when the shooting distance is INF.

[0074] [Variable Distance Data] shows the variable surface distance and BF values ​​when the shooting distance is INF and at a specified shooting magnification.

[0075] [Lens Group Data] shows the surface number of each lens group closest to the object and the composite focal length of the entire group.

[0076] In the following specification values, the focal length f, radius of curvature r, lens surface spacing d, and other length units are all in millimeters (mm) unless otherwise specified; however, this is not a limitation, as optical systems can achieve equivalent optical performance with proportional magnification and proportional reduction.

[0077] Also shown is a list of values ​​corresponding to the conditional expressions in each of these embodiments.

[0078] In the aberration diagrams corresponding to the respective examples, d, g, and C represent the d-line, g-line, and C-line, respectively, and ΔS and ΔM represent the sagittal image surface and meridional image surface, respectively. [Example]

[0079] FIG. 1 is a diagram showing the lens configuration of an inner focus optical system according to a first embodiment of the present invention.

[0080] The lens configuration of the inner focus optical system in FIG. 1 is composed of, in order from the object side to the image side, a first lens group G1 with positive 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 with positive refractive power.

[0081] The first lens group G1 is composed of a biconvex lens, a positive meniscus lens with its convex surface facing the object side, a negative meniscus lens with its convex surface facing the object side, a cemented lens consisting of a biconvex lens and a biconcave lens, a biconcave lens, an aperture stop S, a triplet cemented lens consisting of a biconcave lens, a biconvex lens, and a biconcave lens, and a biconvex lens with an aspherical surface on the image side.

[0082] The second lens group G2 is composed of a positive meniscus lens with its convex surface facing the object side, and focusing from an object at infinity to an object at close range is performed by moving the second lens group G2 toward the object side along the optical axis.

[0083] The third lens group G3 is composed of a negative meniscus lens with its convex surface facing the object side, and focusing from an object at infinity to an object at close range is performed by moving the third lens group G3 toward the image side along the optical axis.

[0084] The fourth lens group G4 is composed of a biconvex lens.

[0085] The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

[0086] Next, the specifications of the inner focus optical system according to the first embodiment are shown below.

[0087] Numerical Example 1 Unit: mm [Face Data] Surface number rd nd vd Object surface ∞ (d0) 1 120.5691 2.7553 1.55032 75.50 2 -160.0471 0.1500 3 40.0090 2.7597 1.90043 37.37 4 115.3070 0.1500 5 33.3087 0.8000 1.48749 70.44 6 16.3755 1.1266 7 21.2919 4.4262 1.90043 37.37 8 -73.1406 0.8000 1.77047 29.74 9 25.4133 2.0292 10 -559.0017 0.8000 1.62004 36.30 11 23.7047 3.5717 12 (Aperture) ∞ 3.1340 13 -17.2091 0.8000 1.77047 29.74 14 31.1532 4.5715 1.90043 37.37 15 -31.5060 0.8000 1.77047 29.74 16 377.4273 0.1500 17 158.6725 4.4020 1.91082 35.25 18* -24.7088 (d18) 19 26.5658 3.1627 1.55032 75.50 20 344.4305 (d20) 21 188.1893 0.8000 1.73037 32.23 22 20.8196 (d22) 23 36.1011 5.1756 1.77250 49.62 24 -47.5836 10.0000 25 ∞ 4.2000 1.51680 64.20 26∞(BF) Image plane ∞ [Aspherical data] 18 sides K 0.00000 A4 8.06818E-06 A6 1.12593E-08 A8 -8.13920E-11 A10 8.42745E-13 A12 -2.38508E-15 [Various data] INF Focal length 36.00 F-number 1.47 Full angle of view 2ω 34.12 Image height Y 11.15 Lens total length 75.00 [Variable Interval Data] INF Magnification 0.025 d0 ∞ 1424.1817 d18 6.0000 5.0929 d20 1.5000 2.7048 d22 6.5000 6.2024 BF 4.4354 4.4359 [Lens group data] Group starting plane focal length G1 1 74.48 G2 19 52.12 G3 21 -32.12 G4 23 27.31 [Example]

[0088] FIG. 6 is a lens configuration diagram of an inner focus optical system according to a second embodiment of the present invention.

[0089] The lens configuration of the inner focus optical system in Figure 6 is composed of, in order from the object side to the image side, a first lens group G1 with positive 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.

[0090] The first lens group G1 is composed of a positive meniscus lens with a convex surface facing the object side, a cemented lens consisting of a biconvex lens and a biconcave lens, a negative meniscus lens with a convex surface facing the object side, an aperture stop S, and a cemented lens consisting of a biconcave lens and a biconvex lens with an aspherical surface on the image side.

[0091] The second lens group G2 is composed of a biconvex lens, and focusing from an object at infinity to an object at a close distance is performed by moving the second lens group G2 toward the object side along the optical axis.

[0092] 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 object at infinity to a close-up object is performed by moving the third lens group G3 toward the image side along the optical axis.

[0093] The fourth lens group G4 is composed of a positive meniscus lens with its 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 the second embodiment are shown below.

[0096] Numerical Example 2 Unit: mm [Face Data] Surface number rd nd vd Object surface ∞ (d0) 1 32.1532 4.1154 1.91082 35.25 2 196.6499 0.1500 3 18.5015 5.5525 1.90043 37.37 4 -114.3549 0.8000 1.85883 30.00 5 17.6043 1.2790 6 30.1018 0.8000 1.77047 29.74 7 11.0560 4.7326 8 (Aperture) ∞ 2.4513 9 -17.5117 0.8000 1.77047 29.74 10 17.0425 4.6641 1.90043 37.37 11* -28.3196 (d11) 12 37.4218 4.7844 1.55032 75.50 13 -20.2599 (d13) 14* 119.5082 0.8000 1.73037 32.23 15* 17.6771 (d15) 16 23.0350 6.1656 2.00100 29.13 17 130.2240 5.0000 18 ∞ 4.2000 1.51680 64.20 19∞(BF) Image plane ∞ [Aspherical data] 11th page 14th page 15th page K 0.00000 0.00000 0.00000 A4 3.40568E-05 6.42803E-05 5.90694E-05 A6 3.08896E-07 -1.08764E-06 -9.89901E-07 A8 -7.42785E-09 6.82573E-09 5.65140E-09 A10 1.27712E-10 -2.59845E-11 -1.95966E-11 A12 -6.83440E-13 0.00000E+00 0.00000E+00 [Various data] INF Focal length 36.35 F-number 1.47 Full angle of view 2ω 33.89 Image height Y 11.15 Lens total length 63.00 [Variable Interval Data] INF Magnification 0.025 d0 ∞ 1436.0578 d11 6.0000 5.5564 d13 1.5000 2.4094 d15 6.5000 6.0342 BF 2.7052 2.7052 [Lens group data] Group starting plane focal length G1 1 145.94 G2 12 24.61 G3 14 -28.50 G4 16 27.18 [Example]

[0097] FIG. 11 is a lens configuration diagram of an inner focus optical system according to a third embodiment of the present invention.

[0098] The lens configuration of the inner focus optical system in Figure 11 is composed of, in order from the object side to the image side, a first lens group G1 with positive 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.

[0099] The first lens group G1 is composed of a biconvex lens, a positive meniscus lens with its convex surface facing the object side, a biconcave lens, an aperture stop S, a cemented lens consisting of a biconcave lens and a biconvex lens, a biconvex lens, and a positive meniscus lens with an aspherical surface on the image side and a convex surface facing the object side.

[0100] The second lens group G2 is composed of a biconvex lens with an aspherical surface on the object side, and focusing from an object at infinity to an object at close range is performed by moving the second lens group G2 toward the object side along the optical axis.

[0101] 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 object at infinity to a close-up object is performed by moving the third lens group G3 toward the image side along the optical axis.

[0102] The fourth lens group G4 is composed of a biconvex lens with aspherical surfaces on both sides.

[0103] The optical filter FL is disposed between the fourth lens group G4 and the image plane I.

[0104] Next, the specifications of the inner focus optical system according to the third embodiment are shown below.

[0105] Numerical Example 3 Unit: mm [Face Data] Surface number rd nd vd Object surface ∞ (d0) 1 47.5338 3.2953 1.90043 37.37 2 -429.6719 0.1500 3 18.5134 4.0120 1.55032 75.50 4 50.8495 1.5531 5 -255.8993 0.8000 1.51742 52.15 6 11.0483 6.0180 7 (Aperture) ∞ 2.3142 8 -29.9203 0.8000 1.84666 23.78 9 14.7655 6.1342 1.90043 37.37 10 -37.1918 0.1500 11 67.9153 2.2650 1.55032 75.50 12 -3354.3128 0.1500 13 32.0044 2.8898 2.00100 29.13 14* 64.4464 (d14) 15* 49.0969 1.7162 1.91082 35.25 16 -895.2742 (d16) 17* 330.0774 0.8000 1.54072 47.20 18* 17.6336 (d18) 19* 102.5653 3.4432 1.71700 47.98 20* -58.5246 5.0000 21 ∞ 4.2000 1.51680 64.20 22∞(BF) Image plane ∞ [Aspherical data] 14th page 15th page 17th page K 0.00000 0.00000 0.00000 A4 -5.28920E-05 -6.36770E-05 2.35364E-04 A6 2.55507E-08 -9.74129E-08 -5.48571E-06 A8 -1.23773E-09 3.58410E-10 4.01858E-08 A10 1.15308E-11 -2.13257E-12 -1.34014E-10 A12 -2.90590E-14 0.00000E+00 0.00000E+00 18th page 19th page 20th page K 0.00000 0.00000 0.00000 A4 3.35086E-04 1.18780E-04 7.06915E-05 A6 -4.79892E-06 2.11642E-07 -8.97179E-08 A8 2.68316E-08 -4.34359E-09 -4.47334E-10 A10 -4.73857E-11 6.26844E-12 -9.00860E-12 A12 0.00000E+00 0.00000E+00 0.00000E+00 [Various data] INF Focal length 35.63 F-number 1.46 Full angle of view 2ω 34.27 Image height Y 11.15 Lens total length 61.00 [Variable Interval Data] INF Magnification 0.025 d0 ∞ 1405.3305 d14 4.0000 3.7000 d16 1.5000 2.3987 d18 5.2170 4.6183 BF 4.5919 4.5919 [Lens group data] Group starting plane focal length G1 1 42.02 G2 15 51.15 G3 17 -34.48 G4 19 52.44

[0106] Example values Example 1 Example 2 Example 3 (1) 0.48 0.25 0.85 (2) 0.69 1.48 0.70 (3) -1.12 -1.28 -1.03 (4) 1.32 1.34 0.68 (5) 0.31 0.48 0.75 (6) 0.71 1.09 0.90 (7) 0.85 0.92 1.05 (8) 4.99 4.09 4.05 [Explanation of symbols]

[0107] G1 First lens group G2 Second 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 with positive 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, wherein when focusing from an infinity object side to a close object side, the second lens group G2 moves toward the object side and the third lens group G3 moves toward the image side, the first lens group G1 and the fourth lens group G4 are fixed with respect to the image plane, an aperture stop S is located within the first lens group G1, and wherein the following condition is satisfied: (2) 0.35<f / f2<2.22 however, f: focal length when the entire system is focused at infinity 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) 0.12<MR<1.70 (3) -2.55<f / f3<-0.52 (4) 0.34<f / f4<2.68 however, MR: Magnification burden of the composite system from the second lens group onwards when the object distance is infinity 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) 0.15<M4<1.0 however, M4: Magnification load of the fourth lens group G4 when the object distance is infinity

4. 4. The inner focus optical system according to claim 1, wherein the following condition is satisfied: (6) 0.35<((M3×M4)^2×(1-M2^2))<2.18 (7) 0.42<|(M4^2×(1-M3^2))|<2.10 however, M2: Magnification load of the second lens group G2 when the object distance is infinity M3: Magnification load of the third lens group G3 when the object distance is infinity M4: Magnification load of the fourth lens group G4 when the object distance is infinity

5. 5. The inner focus optical system according to claim 1, wherein the second lens group G2 having a positive refractive power and the third lens group G3 having a negative refractive power are each composed of a single lens.

6. 6. The inner focus optical system according to claim 1, wherein the following condition is satisfied: (8) 2.03<D / Y<9.98 however, D: Length from the aperture to the image plane Y: Maximum image height

Images