Optical system, optical apparatus, and method for manufacturing optical system

Abstract

To provide a compact and bright optical system having excellent optical performance.SOLUTION: The optical system OL includes, in order from an object side along an optical axis, a front group GA, an intermediate group GM, and a rear group GR, the intermediate group GM includes, in order from the object side along the optical axis, a first focusing lens group GF1 having a positive refractive power and a second focusing lens group GF2 having a positive refractive power, the first focusing lens group GF1 and the second focusing lens group GF2 move along the optical axis along trajectories different from each other during focusing, and the rear group GR includes a negative lens disposed closest to the image plane side, the following conditional expressions are satisfied: 0.01 fF2 / fF1 10.000.50 Y / B f 5.00 where fF1 denotes a focal distance of the first focusing lens group GF1, fF2 denotes a focal distance of the second focusing lens group GF2, Y denotes an image height of the optical system O L, and B f denotes a back focus of the optical system O L.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system, an optical instrument, and a method for manufacturing an optical system. [Background technology]

[0002] Conventionally, optical systems suitable for photo cameras, electronic still cameras, video cameras, etc. have been proposed (see, for example, Patent Document 1). However, it is difficult to obtain bright and good optical performance in such optical systems while making them compact. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-191502 Summary of the Invention

[0004] The optical system according to the present invention comprises a front group, an intermediate group, and a rear group, arranged in order from the object side along the optical axis, the intermediate group comprising a first focusing lens group having positive refractive power and a second focusing lens group having positive refractive power, arranged in order from the object side along the optical axis, the first focusing lens group and the second focusing lens group moving along the optical axis on mutually different loci during focusing, the front group and the rear group being fixed with respect to the image plane, the rear group having a negative lens arranged closest to the image plane in the rear group, and satisfying the following conditional expression: 0.01 <fF2 / fF1<10.00 0.50 <Y / Bf<5.00 where fF1 is the focal length of the first focusing lens group fF2: focal length of the second focusing lens group Y: Image height of the optical system Bf: back focus of the optical system

[0005] An optical device according to the present invention includes the optical system described above.

[0006] A method for manufacturing an optical system according to the present invention is a method for manufacturing an optical system consisting of a front group, an intermediate group, and a rear group, arranged in order from the object side along the optical axis, wherein the intermediate group consists of a first focusing lens group having positive refractive power and a second focusing lens group having positive refractive power, arranged in order from the object side along the optical axis, wherein, during focusing, the first focusing lens group and the second focusing lens group move along the optical axis on different trajectories, the front group and the rear group are fixed with respect to an image plane, and the rear group has a negative lens arranged closest to the image plane in the rear group, and the method includes a step of arranging each lens within a lens barrel so as to satisfy the following conditional expression: 0.01 <fF2 / fF1<10.00 0.50 <Y / Bf<5.00 where fF1 is the focal length of the first focusing lens group fF2: focal length of the second focusing lens group Y: Image height of the optical system Bf: back focus of the optical system [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a diagram showing the lens configuration of an optical system according to Example 1. [Figure 2] 2A and 2B are diagrams showing various aberrations of the optical system according to Example 1 when focused at infinity and when focused at a close distance, respectively. [Figure 3] FIG. 10 is a diagram showing the lens configuration of an optical system according to a second example. [Figure 4] 4A and 4B are diagrams showing various aberrations of the optical system according to Example 2 when focused on infinity and when focused on a close distance, respectively. [Figure 5] FIG. 10 is a diagram showing the lens configuration of an optical system according to Example 3. [Figure 6] 6A and 6B are diagrams showing various aberrations of the optical system according to Example 3 when focused at infinity and when focused at a close distance, respectively. [Figure 7] FIG. 10 is a diagram showing the lens configuration of an optical system according to Example 4. [Figure 8]8A and 8B are diagrams showing various aberrations of the optical system according to Example 4 when focused at infinity and when focused at a close distance, respectively. [Figure 9] FIG. 10 is a diagram showing the lens configuration of an optical system according to Example 5. [Figure 10] 10A and 10B are diagrams showing various aberrations of the optical system according to Example 5 when focused on infinity and when focused on a close distance, respectively. [Figure 11] FIG. 13 is a diagram showing the lens configuration of an optical system according to Example 6. [Figure 12] 12A and 12B are diagrams showing various aberrations of the optical system according to Example 6 when focused on infinity and when focused on a close distance, respectively. [Figure 13] FIG. 13 is a diagram showing the lens configuration of an optical system according to Example 7. [Figure 14] 14A and 14B are diagrams showing various aberrations of the optical system according to Example 7 when focused on infinity and when focused on a close distance, respectively. [Figure 15] FIG. 13 is a diagram showing the lens configuration of an optical system according to Example 8. [Figure 16] 16A and 16B are diagrams showing various aberrations of the optical system according to Example 8 when focused on infinity and when focused on a close distance, respectively. [Figure 17] 1 is a diagram showing the configuration of a camera equipped with an optical system according to an embodiment of the present invention. [Figure 18] 10 is a flowchart illustrating a method for manufacturing an optical system according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] A preferred embodiment of the present invention will now be described. First, a camera (optical device) equipped with an optical system according to this embodiment will be described with reference to FIG. 17. As shown in FIG. 17, this camera 1 is composed of a main body 2 and a photographic lens 3 attached to the main body 2. The main body 2 is equipped with an image sensor 4, a main body control unit (not shown) that controls the operation of the digital camera, and an LCD screen 5. The photographic lens 3 is equipped with an optical system OL consisting of multiple lens groups, and a lens position control mechanism (not shown) that controls the position of each lens group. The lens position control mechanism is composed of a sensor that detects the position of the lens groups, a motor that moves the lens groups back and forth along the optical axis, a control circuit that drives the motor, etc.

[0009] Light from the subject is collected by the optical system OL of the photographing lens 3 and reaches the image plane I of the image sensor 4. The light from the subject that reaches the image plane I is photoelectrically converted by the image sensor 4 and recorded as digital image data in a memory (not shown). The digital image data recorded in the memory can be displayed on the LCD screen 5 in response to a user operation. Note that this camera may be a mirrorless camera or a single-lens reflex camera with a quick-return mirror. The optical system OL shown in FIG. 17 is a schematic representation of an optical system provided in the photographing lens 3, and the lens configuration of the optical system OL is not limited to this configuration.

[0010] Next, an optical system according to this embodiment will be described. As shown in FIG. 1, an optical system OL(1) as an example of the optical system OL according to this embodiment is composed of, arranged in order from the object side along the optical axis, a front group GA, a middle group GM, and a rear group GR. The middle group GM is composed of, arranged in order from the object side along the optical axis, a first focusing lens group GF1 having positive refractive power and a second focusing lens group GF2 having positive refractive power. During focusing, the first focusing lens group GF1 and the second focusing lens group GF2 move along the optical axis on different trajectories, and the front group GA and the rear group GR are fixed relative to the image plane I. The rear group GR has a negative lens (L44) arranged closest to the image plane of the rear group GR.

[0011] With the above-described configuration, the optical system OL according to this embodiment satisfies the following conditional expressions (1) and (2). 0.01 <fF2 / fF1<10.00 ···(1) 0.50 <Y / Bf<5.00 ···(2) where fF1 is the focal length of the first focusing lens group GF1 fF2: focal length of the second focusing lens group GF2 Y: Image height of optical system OL Bf: Back focus of optical system OL

[0012] According to this embodiment, it is possible to obtain an optical system that is small yet bright and has good optical performance, and an optical device including this optical system. The optical system OL according to this embodiment may be the optical system OL(2) shown in Fig. 3, the optical system OL(3) shown in Fig. 5, or the optical system OL(4) shown in Fig. 7. Furthermore, the optical system OL according to this embodiment may be the optical system OL(5) shown in Fig. 9, the optical system OL(6) shown in Fig. 11, the optical system OL(7) shown in Fig. 13, or the optical system OL(8) shown in Fig. 15.

[0013] Conditional expression (1) defines an appropriate relationship between the focal length of the second focusing lens group GF2 and the focal length of the first focusing lens group GF1. By satisfying conditional expression (1), various aberrations such as coma can be effectively corrected.

[0014] If the corresponding value of conditional expression (1) exceeds the upper limit, the refractive power of the first focusing lens group GF1 becomes too strong, making it difficult to correct spherical aberration and coma when focusing on a close object. The effect of this embodiment can be further ensured by setting the upper limit of conditional expression (1) to 8.50, 7.50, 7.00, 5.00, 4.00, 3.50, 2.50, 2.00, or even 1.50.

[0015] If the corresponding value of conditional expression (1) falls below the lower limit, the refractive power of the second focusing lens group GF2 becomes too strong, making it difficult to correct coma and field curvature when focusing on a close-up object. By setting the lower limit of conditional expression (1) to 0.05, or even 0.09, the effect of this embodiment can be further ensured.

[0016] Conditional expression (2) defines an appropriate relationship between the image height of the optical system OL and the back focus of the optical system OL. In this embodiment, the back focus of the optical system OL is the air-equivalent distance on the optical axis from the lens surface of the optical system OL closest to the image plane to the image plane I. By satisfying conditional expression (2), it is possible to obtain an optical system that is compact yet bright and has excellent optical performance. By setting the upper limit of conditional expression (2) to 4.50, 4.00, 3.50, 3.00, 2.50, or even 2.00, the effects of this embodiment can be further ensured. By setting the lower limit of conditional expression (2) to 1.00 or even 1.40, the effects of this embodiment can be further ensured.

[0017] The optical system OL according to this embodiment further has an aperture stop S, and it is desirable that the following conditional expression (3) be satisfied. 0.05 <fSr / fSa<4.00 ···(3) where fSr is the composite focal length of the lens located closer to the image plane than the aperture stop S in the optical system OL when focused at infinity. fSa: The composite focal length of the lens located on the object side of the aperture stop S in the optical system OL when focused at infinity

[0018] Conditional expression (3) defines an appropriate relationship between the composite focal length when the lens in optical system OL is positioned closer to the image plane than aperture stop S and the composite focal length when the lens in optical system OL is positioned closer to the object than aperture stop S and the composite focal length when the lens in optical system OL is positioned closer to the object than aperture stop S. By satisfying conditional expression (3), spherical aberration, coma, and field curvature can be effectively corrected.

[0019] If the corresponding value of conditional expression (3) exceeds the upper limit, the refractive power of the lens in optical system OL that is located closer to the object than aperture stop S becomes too strong, making it difficult to correct spherical aberration, coma, and field curvature. By setting the upper limit of conditional expression (3) to 3.50, 3.00, 2.50, or even 2.30, the effect of this embodiment can be made even more certain.

[0020] If the corresponding value of conditional expression (3) is below the lower limit, the refractive power of the lens in optical system OL that is located closer to the image plane than aperture stop S becomes too strong, making it difficult to correct spherical aberration, coma, and field curvature. By setting the lower limit of conditional expression (3) to 0.13, or even 0.18, the effect of this embodiment can be made even more certain.

[0021] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (4). 0.05 <fF2 / fA<8.00 ···(4) However, fA: focal length of the front group GA

[0022] Conditional expression (4) defines an appropriate relationship between the focal length of the second focusing lens group GF2 and the focal length of the front lens group GA. By satisfying conditional expression (4), various aberrations such as coma and curvature of field can be effectively corrected.

[0023] If the corresponding value of conditional expression (4) exceeds the upper limit, the refractive power of the front group GA becomes too strong, making it difficult to correct spherical aberration, coma, and field curvature. By setting the upper limit of conditional expression (4) to 6.00, 5.00, 4.00, 3.00, 2.00, or even 1.50, the effect of this embodiment can be made more certain.

[0024] If the corresponding value of conditional expression (4) falls below the lower limit, the refractive power of the second focusing lens group GF2 becomes too strong, making it difficult to correct coma and field curvature when focusing on a close-up object. By setting the lower limit of conditional expression (4) to 0.10, or even 0.20, the effect of this embodiment can be further ensured.

[0025] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (5). 0.10<(-fR) / fF2<8.00 (5) However, fR is the focal length of the rear group GR.

[0026] Condition (5) defines an appropriate relationship between the focal length of the rear group GR and the focal length of the second focusing lens group GF2. By satisfying condition (5), coma and curvature of field can be effectively corrected.

[0027] If the corresponding value of conditional expression (5) exceeds the upper limit, the refractive power of the second focusing lens group GF2 becomes too strong, making it difficult to correct coma and field curvature when focusing on a close object. By setting the upper limit of conditional expression (5) to 6.00, 5.00, 4.00, 3.00, or even 2.50, the effect of this embodiment can be further ensured.

[0028] If the corresponding value of conditional expression (5) falls below the lower limit, the refractive power of the rear group GR becomes too strong, making it difficult to correct coma and curvature of field. By setting the lower limit of conditional expression (5) to 0.30, or even 0.60, the effect of this embodiment can be made even more certain.

[0029] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (6). 0.02 <fA / fF1<4.00 ···(6) However, fA: focal length of the front group GA

[0030] Condition (6) defines an appropriate relationship between the focal length of the front group GA and the focal length of the first focusing lens group GF1. By satisfying condition (6), various aberrations such as spherical aberration and coma can be effectively corrected.

[0031] If the corresponding value of conditional expression (6) exceeds the upper limit, the refractive power of the first focusing lens group GF1 becomes too strong, making it difficult to correct spherical aberration and coma when focusing on a close object. By setting the upper limit of conditional expression (6) to 3.50, 3.00, 2.50, or even 2.00, the effect of this embodiment can be made more certain.

[0032] If the corresponding value of conditional expression (6) falls below the lower limit, the refractive power of the front group GA becomes too strong, making it difficult to correct spherical aberration, coma, and field curvature. By setting the lower limit of conditional expression (6) to 0.05, or even 0.08, the effect of this embodiment can be made even more certain.

[0033] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (7). 0.10 <fF1 / (-fR)<8.00 ···(7) However, fR is the focal length of the rear group GR.

[0034] Conditional expression (7) defines an appropriate relationship between the focal length of the first focusing lens group GF1 and the focal length of the rear group GR. By satisfying conditional expression (7), various aberrations such as coma can be effectively corrected.

[0035] If the corresponding value of conditional expression (7) exceeds the upper limit, the refractive power of the rear group GR becomes too strong, making it difficult to correct coma and curvature of field. By setting the upper limit of conditional expression (7) to 6.00, or even 5.00, the effect of this embodiment can be made even more certain.

[0036] If the value corresponding to conditional expression (7) falls below the lower limit, the refractive power of the first focusing lens group GF1 becomes too strong, making it difficult to correct spherical aberration and coma when focusing on a close-up object. By setting the lower limit of conditional expression (7) to 0.20, or even 0.30, the effect of this embodiment can be made even more certain.

[0037] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (8). 0.10 <fA / (-fR)<4.00 ···(8) However, fR is the focal length of the rear group GR.

[0038] Conditional expression (8) defines an appropriate relationship between the focal length of the front group GA and the focal length of the rear group GR. By satisfying conditional expression (8), various aberrations such as coma and curvature of field can be effectively corrected.

[0039] If the corresponding value of conditional expression (8) exceeds the upper limit, the refractive power of the rear group GR becomes too strong, making it difficult to correct coma and curvature of field. By setting the upper limit of conditional expression (8) to 3.00, or even 2.50, the effect of this embodiment can be made even more certain.

[0040] If the corresponding value of conditional expression (8) falls below the lower limit, the refractive power of the front group GA becomes too strong, making it difficult to correct spherical aberration, coma, and field curvature. By setting the lower limit of conditional expression (8) to 0.20, or even 0.30, the effect of this embodiment can be made even more certain.

[0041] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (9). 1.00 <f / Bf<8.00 ···(9) where f is the focal length of the optical system OL

[0042] Conditional expression (9) defines an appropriate relationship between the focal length of the optical system OL and the back focus of the optical system OL. By satisfying conditional expression (9), it is possible to obtain an optical system that is small, yet bright and has good optical performance. By setting the upper limit of conditional expression (9) to 6.00, or even 4.50, the effect of this embodiment can be made more certain. Furthermore, by setting the lower limit of conditional expression (9) to 1.50, or even 2.50, the effect of this embodiment can be made more certain.

[0043] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (10). 0.50 <TL / f<7.00 ···(10) where f is the focal length of the optical system OL TL: Total length of optical system OL

[0044] Conditional expression (10) defines an appropriate relationship between the overall length of the optical system OL and the focal length of the optical system OL. In this embodiment, the overall length of the optical system OL is the distance on the optical axis from the lens surface of the optical system OL closest to the object to the image plane I (however, the distance on the optical axis from the lens surface of the optical system OL closest to the image plane to the image plane I is the air-equivalent distance). By satisfying conditional expression (10), it is possible to obtain an optical system that is compact yet bright and has good optical performance. By setting the upper limit of conditional expression (10) to 6.00, or even 5.00, the effect of this embodiment can be made more certain. By setting the lower limit of conditional expression (10) to 1.00, or even 1.50, the effect of this embodiment can be made more certain.

[0045] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (11). 0.10 <fe / fR<0.90 ···(11) where fe is the focal length of the negative lens element in the rear group GR that is located closest to the image plane. fR: focal length of rear group GR

[0046] Conditional expression (11) defines an appropriate relationship between the focal length of the negative lens element in rear group GR that is located closest to the image plane and the focal length of rear group GR. By satisfying conditional expression (11), various aberrations such as field curvature can be effectively corrected.

[0047] If the corresponding value of conditional expression (11) exceeds the upper limit, the refractive power of the rear group GR becomes too strong, making it difficult to correct coma and curvature of field. By setting the upper limit of conditional expression (11) to 0.85, or even 0.75, the effect of this embodiment can be made even more certain.

[0048] If the value corresponding to conditional expression (11) falls below the lower limit, the refractive power of the negative lens element located closest to the image surface in the rear group GR becomes too strong, making it difficult to correct curvature of field. By setting the lower limit of conditional expression (11) to 0.15, or even 0.20, the effect of this embodiment can be made even more certain.

[0049] The optical system OL according to this embodiment preferably further includes an aperture stop S located between the front group GA and the middle group GM, which makes it possible to correct spherical aberration, coma, and curvature of field when focusing on a close-up object.

[0050] In the optical system OL according to this embodiment, it is desirable that the front group GA has positive refractive power, which makes it possible to correct spherical aberration, coma, and curvature of field.

[0051] In the optical system OL according to this embodiment, it is desirable that the rear group GR has negative refractive power, which makes it possible to correct coma and curvature of field.

[0052] Next, a manufacturing method of the optical system OL according to this embodiment will be outlined with reference to FIG. 18. First, a front group GA, a middle group GM, and a rear group GR are arranged along the optical axis in order from the object side (Step ST1). Next, a first focusing lens group GF1 having positive refractive power and a second focusing lens group GF2 having positive refractive power are arranged in the middle group GM in order from the object side along the optical axis (Step ST2). Next, during focusing, the first focusing lens group GF1 and the second focusing lens group GF2 are configured to move along the optical axis on different trajectories, and the front group GA and the rear group GR are fixed relative to the image plane I (Step ST3). A negative lens is also arranged closest to the image plane of the rear group GR (Step ST4). Then, the lenses are arranged in the lens barrel so as to satisfy at least the above conditional expressions (1) and (2) (Step ST5). This manufacturing method makes it possible to manufacture an optical system that is compact, yet bright and has good optical performance. [Example]

[0053] Optical systems OL according to examples of this embodiment will be described below with reference to the drawings. Figures 1, 3, 5, 7, 9, 11, 13, and 15 are cross-sectional views showing the configurations and refractive power distributions of optical systems OL {OL(1) to OL(8)} according to examples 1 to 8. In the cross-sectional views of the optical systems OL(1) to OL(8) according to examples 1 to 8, arrows indicate the direction of movement of each lens group along the optical axis when focusing from infinity to a close-distance object.

[0054] 1, 3, 5, 7, 9, 11, 13, and 15, each lens group is represented by a combination of the symbol G and a number, and each lens is represented by a combination of the symbol L and a number. In this case, to prevent the symbols and numbers from becoming too numerous and complicated, each example uses its own independent combination of symbols and numbers to represent the lens groups, etc. Therefore, even if the same combination of symbols and numbers is used between examples, this does not mean that the examples have the same configuration.

[0055] Tables 1 to 8 are shown below, with Table 1 showing data on the various elements in Example 1, Table 2 in Example 2, Table 3 in Example 3, Table 4 in Example 4, Table 5 in Example 5, Table 6 in Example 6, Table 7 in Example 7, and Table 8 in Example 8. In each example, the d-line (wavelength λ=587.6 nm) and g-line (wavelength λ=435.8 nm) were selected as the targets for calculating aberration characteristics.

[0056] In the [Overall Specifications] table, f is the focal length of the entire lens system, FNO is the F-number, ω is the half angle of view (unit: ° (degrees)), and Y is the image height. TL is the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image plane when focused at infinity, plus Bf (back focus), and Bf is the distance on the optical axis from the lens surface closest to the image plane to the image plane when focused at infinity (air equivalent distance).

[0057] In the table of [Overall Specifications], fA indicates the focal length of the front group. fR indicates the focal length of the rear group. fF1 indicates the focal length of the first focusing lens group. fF2 indicates the focal length of the second focusing lens group. fSa indicates the composite focal length of the lens located closer to the object than the aperture stop in the optical system when focused at infinity. fSr indicates the composite focal length of the lens located closer to the image plane than the aperture stop in the optical system when focused at infinity. fe indicates the focal length of the negative lens located closest to the image plane in the rear group.

[0058] In the [Lens Specifications] table, the surface number indicates the order of the optical surface from the object side along the direction of light ray travel, R is the radius of curvature of each optical surface (surfaces whose center of curvature is on the image side have a positive value), D is the surface spacing, which is the distance on the optical axis from each optical surface to the next optical surface (or image plane), nd is the refractive index of the optical element material with respect to the d-line, and νd is the Abbe number of the optical element material with respect to the d-line. The "∞" next to the radius of curvature indicates a flat surface or an aperture, and (stop S) indicates the aperture stop S. The refractive index of air, nd = 1.00000, is omitted. If the optical surface is aspherical, an * is added to the surface number, and the paraxial radius of curvature is shown in the "radius of curvature R" column.

[0059] In the [Aspherical Data] table, the shape of the aspherical surface shown in [Lens Specifications] is expressed by the following formula (A). X(y) is the distance (sag) along the optical axis from the tangent plane at the vertex of the aspherical surface to the position on the aspherical surface at height y, R is the radius of curvature of the reference sphere (paraxial radius of curvature), κ is the conic constant, and Ai is the ith aspherical coefficient. "En" represents "×10-n." For example, 1.234E-05 = 1.234×10-5. The second-order aspherical coefficient A2 is 0, so its description is omitted.

[0060] X(y)=(y2 / R) / {1+(1-κ×y2 / R2)1 / 2}+A4×y4+A6×y6+A8×y8+A10×y10 …(A)

[0061] The [Variable Distance Data] table shows the surface spacing for surface number i, which is specified as (Di) in the [Lens Specifications] table. The [Variable Distance Data] table also shows the surface spacing when focused at infinity and when focused at close distances. In the [Variable Distance Data] table, f represents the focal length of the entire lens system, and β represents the magnification. Furthermore, D0 represents the distance from the object to the optical surface closest to the object in the optical system.

[0062] The [Lens Group Data] table shows the starting surface (the surface closest to the object) and focal length of each lens group.

[0063] In the following, for all specifications, the focal length f, radius of curvature R, surface spacing D, and other lengths are generally expressed in "mm" unless otherwise specified, but this is not limited to this, as the same optical performance can be obtained even when the optical system is proportionally enlarged or reduced.

[0064] The explanation of the tables up to this point is common to all the embodiments, and duplicate explanations will be omitted below.

[0065] (First Example) The first embodiment will be described with reference to FIGS. 1 and 2 and Table 1. FIG. 1 illustrates the lens configuration of the optical system according to the first embodiment. The optical system OL(1) according to the first embodiment is composed of, arranged along the optical axis from the object 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 positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I. The sign (+) or (-) attached to each lens group symbol indicates the refractive power of the lens group, and this is the same in all the following embodiments.

[0066] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, the second lens group G2 and the third lens group G3 constitute the middle group GM, and the fourth lens group G4 constitutes the rear group GR. Furthermore, the second lens group G2 corresponds to the first focusing lens group GF1, and the third lens group G3 corresponds to the second focusing lens group GF2.

[0067] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L11, a cemented positive lens formed by cementing a biconvex positive lens L12 and a negative meniscus lens L13 with its concave surface facing the object side.

[0068] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a cemented negative lens formed by cementing together a biconcave negative lens L21 and a positive meniscus lens L22 with a convex surface facing the object side, and a biconvex positive lens L23. The positive lens L23 is a hybrid lens formed by providing a resin layer on the image-side surface of a glass lens body. The image-side surface of the resin layer is aspherical, and the positive lens L23 is a hybrid aspherical lens. In the "Lens Specifications" described below, surface number 10 indicates the object-side surface of the lens body, surface number 11 indicates the image-side surface of the lens body and the object-side surface of the resin layer (the surface where the two are cemented), and surface number 12 indicates the image-side surface of the resin layer.

[0069] The third lens group G3 is composed of a biconvex positive lens L31. The positive lens L31 is a hybrid lens composed of a glass lens body with a resin layer provided on the image-side surface of the lens body. The image-side surface of the resin layer is aspherical, making the positive lens L31 a hybrid aspherical lens. In the Lens Specifications section described below, surface number 13 indicates the object-side surface of the lens body, surface number 14 indicates the image-side surface of the lens body and the object-side surface of the resin layer (the surface where the two are cemented), and surface number 15 indicates the image-side surface of the resin layer.

[0070] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a cemented positive lens formed by cementing together a biconcave negative lens L41 and a biconvex positive lens L42, a biconcave negative lens L43, and a plano-concave negative lens L44 with its flat surface facing the image surface. An image surface I is located on the image side of the fourth lens group G4.

[0071] Table 1 below lists the values ​​of the specifications of the optical system according to the first example.

[0072] (Table 1) [Overall specifications] f=36.050 FNO=1.442 ω=31.814 Y=20.374 TL=83.685 Bf=12.113 fA=154.383 fR=-70.566 fF1=150.000 fF2=42.786 fSa=154.383 fSr=41.385 fe=-49.090 [Lens specifications] Surface number RD nd νd 1 -84.278 1.000 1.48749 70.31 2 34.272 0.582 3 42.331 6.737 1.83481 42.73 4 -39.159 0.900 1.76182 26.58 5 -167.335 1.600 6∞ (D6) (Aperture S) 7 -23.995 0.900 1.64769 33.73 8 28.408 5.263 1.83481 42.73 9 214.240 0.100 10 69.377 5.846 1.83481 42.73 11 -52.510 0.100 1.56093 36.64 12* -50.272 (D12) 13 133.009 7.274 1.77250 49.62 14 -47.184 0.100 1.56093 36.64 15* -41.494 (D15) 16 -101.299 1.000 1.68893 31.16 17 37.985 11.824 1.83481 42.73 18 -43.191 0.100 19 -79.644 1.000 1.78472 25.64 20 863.090 6.024 21 -30.438 1.300 1.62004 36.40 22∞Bf [Aspherical data] Side 12 κ=1.0000,A4=9.82707E-06,A6=8.10431E-09,A8=-4.53816E-11,A10=8.08855E-14 Page 15 κ=1.0000,A4=7.20448E-06,A6=3.36893E-10,A8=3.34430E-11,A10=-3.62441E-14 [Variable Interval Data] Infinity focus Close focus f=36.050 β=-0.03333 D0 ∞ 1073.885 D6 13.904 12.690 D12 4.519 4.847 D15 1.500 2.386 Bf 12.113 12.113 [Lens group data] Group starting plane focal length G1 1 154.383 G2 7 150.000 G3 13 42.786 G4 16 -70.566

[0073] FIG. 2A shows various aberration diagrams for the optical system of Example 1 when focusing at infinity. FIG. 2B shows various aberration diagrams for the optical system of Example 1 when focusing at close distances. In each aberration diagram for when focusing at infinity, FNO indicates the F-number, and Y indicates the image height. In each aberration diagram for when focusing at close distances, NA indicates the numerical aperture, and Y indicates the image height. Note that the spherical aberration diagram shows the F-number or numerical aperture value corresponding to the maximum aperture, the astigmatism diagram and distortion diagram show the maximum image height, and the coma diagram shows the value of each image height. d indicates the d-line (wavelength λ=587.6 nm), and g indicates the g-line (wavelength λ=435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal image plane, and the dashed line indicates the meridional image plane. Note that the same symbols as in this example are used in the aberration diagrams of each example shown below, and redundant explanations will be omitted.

[0074] From the various aberration diagrams, it can be seen that the optical system according to Example 1 has excellent imaging performance, with various aberrations being well corrected not only when focusing at infinity but also when focusing at close distances.

[0075] (Second Example) The second example will be described with reference to FIGS. 3 and 4 and Table 2. FIG. 3 shows the lens configuration of the optical system according to the second example. The optical system OL(2) according to the second example is composed of, arranged along the optical axis from the object 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 positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I.

[0076] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, the second lens group G2 and the third lens group G3 constitute the middle group GM, and the fourth lens group G4 constitutes the rear group GR. Furthermore, the second lens group G2 corresponds to the first focusing lens group GF1, and the third lens group G3 corresponds to the second focusing lens group GF2.

[0077] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L11 with its convex surface facing the object side, a positive meniscus lens L12 with its convex surface facing the object side, and a negative meniscus lens L13 with its convex surface facing the object side. The object-side lens surface of the positive meniscus lens L12 is aspherical.

[0078] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a cemented negative lens formed by cementing together a biconcave negative lens L21 and a positive meniscus lens L22 with a convex surface facing the object side, and a biconvex positive lens L23. The positive lens L23 is a hybrid lens formed by providing a resin layer on the image-side surface of a glass lens body. The image-side surface of the resin layer is aspherical, and the positive lens L23 is a hybrid aspherical lens. In the "Lens Specifications" described below, surface number 11 indicates the object-side surface of the lens body, surface number 12 indicates the image-side surface of the lens body and the object-side surface of the resin layer (the surface where the two are cemented), and surface number 13 indicates the image-side surface of the resin layer.

[0079] The third lens group G3 is composed of a biconvex positive lens L31. The positive lens L31 is a hybrid lens composed of a glass lens body with a resin layer provided on the image-side surface of the lens body. The image-side surface of the resin layer is aspherical, making the positive lens L31 a hybrid aspherical lens. In the "Lens Specifications" described below, surface number 14 indicates the object-side surface of the lens body, surface number 15 indicates the image-side surface of the lens body and the object-side surface of the resin layer (the surface where the two are cemented), and surface number 16 indicates the image-side surface of the resin layer.

[0080] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a cemented positive lens formed by cementing together a positive meniscus lens L41 with its concave surface facing the object side and a negative meniscus lens L42 with its concave surface facing the object side, a biconcave negative lens L43, and a plano-concave negative lens L44 with its flat surface facing the image surface side. An image surface I is located on the image side of the fourth lens group G4.

[0081] Table 2 below lists the values ​​of the specifications of the optical system according to the second example.

[0082] (Table 2) [Overall specifications] f=48.500 FNO=1.442 ω=24.256 Y=21.413 TL=92.309 Bf=12.113 fA=144.537 fR=-64.985 fF1=141.932 fF2=42.786 fSa=144.537 fSr=45.388 fe=-398.038 [Lens specifications] Surface number RD nd νd 1 44.354 3.671 1.83481 42.73 2 68.031 2.679 3* 30.946 5.657 1.83481 42.73 4 119.179 0.686 5 456.720 0.900 1.59270 35.27 6 23.170 5.704 7∞ (D7) (S aperture) 8 -19.295 0.900 1.64769 33.72 9 24.301 6.226 1.83481 42.73 10 222.101 0.100 11 51.221 7.224 1.77250 49.62 12 -44.866 0.100 1.56093 36.64 13* -44.287 (D13) 14 51.773 6.423 1.77250 49.62 15 -154.916 0.100 1.56093 36.64 16* -74.031 (D16) 17 -510.487 12.769 1.85026 32.35 18 -20.236 1.000 1.90265 35.73 19 -61.076 0.100 20 -98.851 1.024 1.75520 27.57 21 48.753 4.694 22 -235.917 1.300 1.59270 35.27 23∞Bf [Aspherical data] 3rd page κ=1.0000,A4=1.39886E-06,A6=7.46585E-09,A8=-1.84946E-11,A10=7.06419E-14 Page 13 κ=1.0000,A4=6.25043E-06,A6=7.63434E-09,A8=-2.42103E-12,A10=2.61079E-14 Page 16 κ=1.0000,A4=1.51632E-05,A6=-2.12876E-09,A8=3.12457E-11,A10=-4.64496E-14 [Variable Interval Data] Infinity focus Close focus f=48.500 β=-0.03333 D0 ∞ 1427.370 D7 12.239 11.399 D13 5.200 4.948 D16 1.500 2.591 Bf 12.113 12.113 [Lens group data] Group starting plane focal length G1 1 144.537 G2 8 141.932 G3 14 42.786 G4 17 -64.985

[0083] Fig. 4(A) is a diagram showing various aberrations of the optical system according to Example 2 when focusing at infinity. Fig. 4(B) is a diagram showing various aberrations of the optical system according to Example 2 when focusing at close range. It can be seen from the diagrams that the optical system according to Example 2 has excellent imaging performance, with various aberrations being well corrected not only when focusing at infinity but also when focusing at close range.

[0084] (Third Example) The third example will be described with reference to FIGS. 5 to 6 and Table 3. FIG. 5 shows the lens configuration of the optical system according to the third example. The optical system OL(3) according to the third example is composed of, arranged along the optical axis from the object 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 positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I.

[0085] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, the second lens group G2 and the third lens group G3 constitute the middle group GM, and the fourth lens group G4 constitutes the rear group GR. Furthermore, the second lens group G2 corresponds to the first focusing lens group GF1, and the third lens group G3 corresponds to the second focusing lens group GF2.

[0086] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a plano-concave negative lens L11 with its flat surface facing the object side, and a cemented positive lens formed by cementing together a biconvex positive lens L12 and a biconcave negative lens L13.

[0087] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a cemented negative lens formed by cementing together a biconcave negative lens L21 and a positive meniscus lens L22 with a convex surface facing the object side, and a biconvex positive lens L23. The positive lens L23 is a hybrid lens formed by providing a resin layer on the image-side surface of a glass lens body. The image-side surface of the resin layer is aspherical, and the positive lens L23 is a hybrid aspherical lens. In the "Lens Specifications" described below, surface number 10 indicates the object-side surface of the lens body, surface number 11 indicates the image-side surface of the lens body and the object-side surface of the resin layer (the surface where the two are cemented), and surface number 12 indicates the image-side surface of the resin layer.

[0088] The third lens group G3 is composed of a biconvex positive lens L31. The positive lens L31 is a hybrid lens composed of a glass lens body with a resin layer provided on the image-side surface of the lens body. The image-side surface of the resin layer is aspherical, making the positive lens L31 a hybrid aspherical lens. In the Lens Specifications section described below, surface number 13 indicates the object-side surface of the lens body, surface number 14 indicates the image-side surface of the lens body and the object-side surface of the resin layer (the surface where the two are cemented), and surface number 15 indicates the image-side surface of the resin layer.

[0089] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a cemented positive lens formed by cementing together a biconcave negative lens L41 and a biconvex positive lens L42, a negative meniscus lens L43 with its concave surface facing the object side, and a plano-concave negative lens L44 with its flat surface facing the image surface side. An image surface I is located on the image side of the fourth lens group G4.

[0090] Table 3 below lists the values ​​of the specifications of the optical system according to the third example.

[0091] (Table 3) [Overall specifications] f=36.050 FNO=1.442 ω=31.808 Y=20.358 TL=80.563 Bf=12.113 fA=175.868 fR=-103.535 fF1=100.040 fF2=50.621 fSa=175.868 fSr=38.887 fe=-55.498 [Lens specifications] Surface number RD nd νd 1 ∞ 1.000 1.48749 70.32 2 27.539 0.516 3 31.701 6.527 1.83481 42.73 4 -58.413 0.900 1.72825 28.38 5 142.453 2.116 6∞ (D6) (Aperture S) 7 -23.996 0.900 1.59270 35.27 8 27.203 5.321 1.83481 42.73 9 403.040 0.124 10 75.848 5.128 1.83481 42.73 11 -58.068 0.100 1.56093 36.64 12* -54.564 (D12) 13 1598.814 5.843 1.75500 52.34 14 -40.976 0.100 1.56093 36.64 15* -38.468 (D15) 16 -119.723 1.000 1.72825 28.38 17 34.445 12.585 1.90265 35.73 18 -36.878 0.100 19 -43.561 2.607 1.84666 23.80 20 -236.442 4.820 21 -32.894 1.300 1.59270 35.27 22∞Bf [Aspherical data] Side 12 κ=1.0000,A4=1.47674E-05,A6=-1.08656E-08,A8=8.95106E-12,A10=-3.68687E-15 Page 15 κ=1.0000,A4=4.77686E-06,A6=1.19495E-08,A8=1.37062E-11,A10=3.29111E-14 [Variable Interval Data] Infinity focus Close focus f=36.050 β=-0.03333 D0 ∞ 1081.803 D6 12.622 10.849 D12 3.342 4.228 D15 1.500 2.387 Bf 12.113 12.113 [Lens group data] Group starting plane focal length G1 1 175.868 G2 7 100.040 G3 13 50.621 G4 16 -103.535

[0092] Fig. 6(A) is a diagram showing various aberrations of the optical system according to Example 3 when focusing at infinity. Fig. 6(B) is a diagram showing various aberrations of the optical system according to Example 3 when focusing at close range. It can be seen from the diagrams that the optical system according to Example 3 has excellent imaging performance, with various aberrations being well corrected not only when focusing at infinity but also when focusing at close range.

[0093] (Fourth Example) Example 4 will be described with reference to FIGS. 7 to 8 and Table 4. FIG. 7 shows the lens configuration of the optical system according to Example 4. The optical system OL(4) according to Example 4 is composed of, arranged along the optical axis from the object 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 positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I.

[0094] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, the second lens group G2 and the third lens group G3 constitute the middle group GM, and the fourth lens group G4 constitutes the rear group GR. Furthermore, the second lens group G2 corresponds to the first focusing lens group GF1, and the third lens group G3 corresponds to the second focusing lens group GF2.

[0095] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L11 with a convex surface facing the object side, a negative meniscus lens L12 with a convex surface facing the object side, a cemented positive lens formed by cementing a biconvex positive lens L13 and a biconcave negative lens L14, a cemented negative lens formed by cementing a biconcave negative lens L15 and a biconvex positive lens L16, a biconvex positive lens L17, a biconvex positive lens L18, and a cemented negative lens formed by cementing a biconcave negative lens L19 and a biconvex positive lens L110. The lens surface of the negative meniscus lens L12 facing the image plane is aspheric.

[0096] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L21 and a biconvex positive lens L22.

[0097] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L31 with its convex surface facing the object side and a positive meniscus lens L32 with its convex surface facing the object side. The positive meniscus lens L31 has an aspherical lens surface facing the image side. The positive meniscus lens L32 has an aspherical lens surface facing the image side.

[0098] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L41 with its concave surface facing the object side and a biconcave negative lens L42. An image surface I is located on the image side of the fourth lens group G4.

[0099] Table 4 below lists the values ​​of the specifications of the optical system according to the fourth example.

[0100] (Table 4) [Overall specifications] f=34.301 FNO=1.230 ω=32.681 Y=21.600 TL=145.455 Bf=11.456 fA=60.284 fR=-155.922 fF1=493.944 fF2=77.173 fSa=60.284 fSr=87.232 fe=-52.564 [Lens specifications] Surface number RD nd νd 1 96.047 2.000 1.48749 70.31 2 28.087 9.219 3 66.416 1.800 1.58887 61.13 4* 42.041 2.388 5 47.837 8.233 2.00100 29.12 6 -645.006 1.500 1.49782 82.57 7 35.910 11.438 8 -33.782 1.500 1.85451 25.15 9 80.983 5.585 1.56732 42.58 10 -217.995 0.200 11 237.343 8.059 2.00069 25.46 12 -51.294 0.200 13 44.432 10.369 1.59349 67.00 14 -144.859 2.518 15 -99.402 1.500 1.69895 30.13 16 27.200 14.331 1.59319 67.90 17 -86.856 2.000 18∞ (D18) (Aperture S) 19 -38.048 1.300 1.68376 37.64 20 178.836 0.200 21 41.104 9.000 1.59349 67.00 22 -68.514 (D22) 23 36.893 6.200 1.85108 40.12 24* 75.937 4.486 25 157.349 2.500 1.77387 47.25 26* 161.771 (D26) 27 -597.200 3.598 1.94595 17.98 28 -68.766 1.916 29 -40.274 1.500 1.73037 32.23 30 834.207 Bf [Aspherical data] Side 4 κ=1.0000,A4=-1.39004E-06,A6=-9.76153E-10,A8=-1.35116E-12,A10=-7.50960E-16 Page 24 κ=1.0000,A4=-4.67477E-06,A6=-5.48120E-09,A8=3.46635E-11,A10=-1.11525E-14 Page 26 κ=1.0000,A4=2.09207E-05,A6=2.10855E-08,A8=-1.68530E-11,A10=-2.78769E-14 [Variable Interval Data] Infinity focus Close focus f=34.301 β=-0.03333 D0 ∞ 993.600 D18 13.152 11.783 D22 2.047 2.000 D26 5.262 6.678 Bf 11.456 11.456 [Lens group data] Group starting plane focal length G1 1 60.284 G2 19 493.944 G3 23 77.173 G4 27 -155.922

[0101] Fig. 8(A) is a diagram showing various aberrations of the optical system according to Example 4 when focusing at infinity. Fig. 8(B) is a diagram showing various aberrations of the optical system according to Example 4 when focusing at close range. It can be seen from the diagrams that the optical system according to Example 4 has excellent imaging performance, with various aberrations being well corrected not only when focusing at infinity but also when focusing at close range.

[0102] (Fifth Example) Example 5 will be described with reference to FIGS. 9 and 10 and Table 5. FIG. 9 shows the lens configuration of an optical system according to Example 5. The optical system OL(5) according to Example 5 is composed of, arranged along the optical axis from the object 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 positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I.

[0103] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, the second lens group G2 and the third lens group G3 constitute the middle group GM, and the fourth lens group G4 constitutes the rear group GR. Furthermore, the second lens group G2 corresponds to the first focusing lens group GF1, and the third lens group G3 corresponds to the second focusing lens group GF2.

[0104] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L11 with a convex surface facing the object side, a negative meniscus lens L12 with a convex surface facing the object side, a cemented positive lens formed by cementing a biconvex positive lens L13 and a biconcave negative lens L14, a cemented negative lens formed by cementing a biconcave negative lens L15 and a biconvex positive lens L16, a biconvex positive lens L17, a biconvex positive lens L18, and a cemented negative lens formed by cementing a biconcave negative lens L19 and a biconvex positive lens L110. The lens surface of the negative meniscus lens L12 facing the image plane is aspheric.

[0105] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L21 and a biconvex positive lens L22.

[0106] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a cemented positive lens formed by cementing together a biconvex positive lens L31 and a biconcave negative lens L32, and a negative meniscus lens L33 with its concave surface facing the object side. Both lens surfaces of the negative meniscus lens L33 are aspherical.

[0107] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L41 with its concave surface facing the object side and a biconcave negative lens L42. An image surface I is located on the image side of the fourth lens group G4.

[0108] Table 5 below lists the values ​​of the specifications of the optical system according to the fifth example.

[0109] (Table 5) [Overall specifications] f=34.300 FNO=1.230 ω=32.676 Y=21.600 TL=145.455 Bf=11.455 fA=65.214 fR=-165.983 fF1=629.134 fF2=70.033 fSa=65.214 fSr=80.285 fe=-56.319 [Lens specifications] Surface number RD nd νd 1 72.093 2.000 1.48749 70.31 2 27.081 11.466 3 105.428 1.800 1.51680 64.13 4* 49.653 1.202 5 47.334 7.850 2.00100 29.12 6 -2063.273 1.500 1.49782 82.57 7 34.755 11.769 8 -32.107 1.500 1.85451 25.15 9 82.520 5.950 1.67003 47.14 10 -198.954 0.200 11 391.739 7.906 2.00069 25.46 12 -48.789 0.200 13 41.194 11.022 1.59349 67.00 14 -135.101 1.669 15 -112.838 1.500 1.73037 32.23 16 27.200 13.277 1.59319 67.90 17 -122.895 2.000 18∞ (D18) (Aperture S) 19 -42.056 1.300 1.68376 37.64 20 240.838 0.200 21 38.726 7.500 1.59319 67.90 22 -118.915 (D22) 23 42.490 7.198 1.83481 42.73 24 -124.265 1.500 1.68376 37.64 25 96.988 5.998 26* -257.390 2.500 1.77387 47.25 27* -264.366 (D27) 28 -531.885 3.492 1.94595 17.98 29 -71.866 1.741 30 -43.260 1.500 1.73037 32.23 31 848.999 Bf [Aspherical Data] The 4th surface κ = 1.0000, A4 = -1.34774E-06, A6 = -9.46928E-10, A8 = -1.46439E-12, A10 = -3.40961E-16 The 26th surface κ = 1.0000, A4 = -7.46350E-06, A6 = 6.20342E-08, A8 = -1.63956E-10, A10 = 4.03734E-14 The 27th surface κ = 1.0000, A4 = 9.35182E-06, A6 = 7.30804E-08, A8 = -1.33669E-10, A10 = 1.93285E-14 [Variable Interval Data] Infinity Focus State Near Focus State f = 34.300 β = -0.03333 D0 ∞ 994.412 D18 12.611 11.246 D22 2.244 2.268 D27 3.404 4.744 Bf 11.455 11.455 [Lens Group Data] Group Starting Surface Focal Length G1 1 65.214 G2 19 629.134 G3 23 70.033 G4 27 -165.983

[0110] Fig. 10(A) is a diagram showing various aberrations when the optical system according to Example 5 is focused at infinity. Fig. 10(B) is a diagram showing various aberrations when the optical system according to Example 5 is focused at close range. From these aberration diagrams, it can be seen that the optical system according to Example 5 has excellent imaging performance, with various aberrations being well corrected not only when focused at infinity but also when focused at close range.

[0111] (Sixth Example) Example 6 will be described with reference to FIGS. 11 and 12 and Table 6. FIG. 11 shows the lens configuration of an optical system according to Example 6. The optical system OL(6) according to Example 6 is composed of, arranged along the optical axis from the object 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 positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I.

[0112] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, the second lens group G2 and the third lens group G3 constitute the middle group GM, and the fourth lens group G4 constitutes the rear group GR. Furthermore, the second lens group G2 corresponds to the first focusing lens group GF1, and the third lens group G3 corresponds to the second focusing lens group GF2.

[0113] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L11 with a convex surface facing the object side, a cemented positive lens formed by cementing a biconvex positive lens L12 and a biconcave negative lens L13, a cemented negative lens formed by cementing a biconcave negative lens L14 and a positive meniscus lens L15 with a convex surface facing the object side, a cemented positive lens formed by cementing a biconvex positive lens L16 and a negative meniscus lens L17 with a concave surface facing the object side, a positive meniscus lens L18 with a convex surface facing the object side, and a cemented negative lens formed by cementing a biconvex positive lens L19 and a biconcave negative lens L110.

[0114] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L21 with its concave surface facing the object side, a biconvex positive lens L22, and a negative meniscus lens L23 with its concave surface facing the object side. Both lens surfaces of the negative meniscus lens L23 are aspherical.

[0115] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L31 with its concave surface facing the object side and a negative meniscus lens L32 with its concave surface facing the object side. The positive meniscus lens L31 has an aspherical lens surface facing the image side. The negative meniscus lens L32 has an aspherical lens surface facing the object side.

[0116] The fourth lens group G4 is composed of, in order from the object side along the optical axis, a positive meniscus lens L41 with its concave surface facing the object side and a biconcave negative lens L42 cemented together. An image surface I is located on the image side of the fourth lens group G4.

[0117] Table 6 below lists the values ​​of the specifications of the optical system according to the sixth example.

[0118] (Table 6) [Overall specifications] f=34.300 FNO=1.228 ω=32.697 Y=21.600 TL=155.455 Bf=11.455 fA=75.723 fR=-60.553 fF1=69.782 fF2=58.312 fSa=75.723 fSr=61.522 fe=-26.934 [Lens specifications] Surface number RD nd νd 1 81.239 2.000 1.59349 67.00 2 29.403 11.650 3 97.417 9.313 1.90265 35.77 4 -66.592 1.500 1.51742 52.20 5 37.688 11.679 6 -36.576 3.997 1.73037 32.23 7 57.862 5.275 1.94595 17.98 8 437.731 0.200 9 137.189 14.813 1.84850 43.79 10 -31.982 1.500 1.85451 25.15 11 -58.341 0.200 12 50.708 7.542 1.59319 67.90 13 173.475 0.200 14 50.175 13.955 1.59319 67.90 15 -45.041 1.500 1.64769 33.73 16 49.712 5.575 17∞ (D17) (Aperture S) 18 -42.349 1.500 1.61266 44.46 19 -303.712 0.200 20 30.793 9.330 1.59349 67.00 21 -73.903 0.200 22* -74.759 2.000 1.88202 37.23 23* -78.949 (D23) 24 -117.169 3.976 1.77387 47.25 25* -26.746 0.564 26* -30.019 3.648 1.58887 61.13 27 -41.705 (D27) 28 -65.973 6.366 1.94595 17.98 29 -27.107 1.500 1.77047 29.74 30 90.644 Bf [Aspherical data] Page 22 κ=1.0000,A4=1.73688E-05,A6=9.00046E-08,A8=-3.66508E-10,A10=3.45942E-13 Page 23 κ=1.0000,A4=2.84915E-05,A6=9.29029E-08,A8=-3.03655E-10,A10=1.96904E-13 Page 25 κ=1.0000,A4=5.79685E-05,A6=-1.66905E-07,A8=4.04878E-10,A10=-3.50430E-13 Page 26 κ=1.0000,A4=6.83994E-05,A6=-2.43826E-07,A8=5.82093E-10,A10=-5.75702E-13 [Variable Interval Data] Infinity focus Close focus f=34.300 β=-0.03333 D0 ∞ 988.825 D17 13.387 12.265 D23 8.429 8.961 D27 2.000 2.591 Bf 11.455 11.455 [Lens group data] Group starting plane focal length G1 1 75.723 G2 18 69.782 G3 24 58.312 G4 28 -60.553

[0119] Fig. 12(A) is a diagram showing various aberrations when the optical system according to Example 6 is focused at infinity. Fig. 12(B) is a diagram showing various aberrations when the optical system according to Example 6 is focused at close range. From these aberration diagrams, it can be seen that the optical system according to Example 6 has excellent imaging performance, with various aberrations being well corrected not only when focused at infinity but also when focused at close range.

[0120] (Seventh Example) Example 7 will be described with reference to FIGS. 13 and 14 and Table 7. FIG. 13 shows the lens configuration of an optical system according to Example 7. The optical system OL(7) according to Example 7 is composed of, arranged along the optical axis from the object 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 positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I.

[0121] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, the second lens group G2 and the third lens group G3 constitute the middle group GM, and the fourth lens group G4 constitutes the rear group GR. Furthermore, the second lens group G2 corresponds to the first focusing lens group GF1, and the third lens group G3 corresponds to the second focusing lens group GF2.

[0122] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L11 with a convex surface facing the object side, a cemented positive lens formed by cementing together a negative meniscus lens L12 with a convex surface facing the object side and a positive meniscus lens L13 with a convex surface facing the object side, a cemented negative lens formed by cementing together a biconvex positive lens L14 and a biconcave negative lens L15, a biconcave negative lens L16, a biconvex positive lens L17, a biconvex positive lens L18, and a cemented negative lens formed by cementing together a biconcave negative lens L19 and a biconvex positive lens L110.

[0123] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L21 with its concave surface facing the object side, and a biconvex positive lens L22.

[0124] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L31 and a biconvex positive lens L32. The negative lens L31 has an aspherical lens surface facing the image plane. The positive lens L32 has aspherical lens surfaces on both sides.

[0125] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a biconvex positive lens L41 and a biconcave negative lens L42. An image surface I is located on the image side of the fourth lens group G4.

[0126] Table 7 below lists the values ​​of the specifications of the optical system according to the seventh example.

[0127] (Table 7) [Overall specifications] f=34.300 FNO=1.230 ω=32.684 Y=21.600 TL=157.455 Bf=11.455 fA=70.486 fR=-192.806 fF1=74.747 fF2=247.083 fSa=70.486 fSr=72.472 fe=-39.734 [Lens specifications] Surface number RD nd νd 1 66.961 2.000 1.81600 46.59 2 32.457 11.809 3 128.665 1.800 1.59319 67.90 4 40.741 9.802 2.00069 25.46 5 215.641 0.200 6 110.947 7.041 1.81600 46.59 7 -112.594 1.500 1.51680 64.14 8 28.007 12.084 9 -40.962 8.018 1.73037 32.23 10 857.978 0.200 11 70.201 9.539 1.81600 46.59 12 -61.720 0.200 13 54.810 7.279 1.59349 67.00 14 -212.179 2.494 15 -66.201 1.500 1.73037 32.23 16 27.501 13.807 1.59319 67.90 17 -57.491 2.000 18∞ (D18) (Aperture S) 19 -41.015 1.300 1.56732 42.58 20 -310.485 0.200 21 38.747 7.973 1.77250 49.62 22 -146.553 (D22) 23 -42.724 1.500 1.62004 36.40 24* 60.145 0.200 25* 58.069 3.682 1.85108 40.12 26* -62.761 (D26) 27 154.307 8.500 1.94595 17.98 28 -76.392 1.740 29 -47.089 3.595 1.75520 27.57 30 85.433 Bf [Aspherical data] The 24th surface κ = 1.0000, A4 = -1.09574E-04, A6 = 3.34832E-07, A8 = -5.81576E-10, A10 = 4.32381E-13 The 25th surface κ = 1.0000, A4 = -7.33927E-05, A6 = 3.59893E-07, A8 = -6.97315E-10, A10 = 4.91900E-13 The 26th surface κ = 1.0000, A4 = 1.43166E-05, A6 = 1.17989E-07, A8 = -2.22684E-10, A10 = 1.31507E-13 [Variable interval data] Infinity focus state, Close focus state f = 34.300 β = -0.03333 D0 ∞ 987.480 D18 16.159 14.666 D22 7.879 7.859 D26 2.000 3.512 Bf 11.455 11.455 [Lens group data] Group, Starting surface, Focal length G1 1 70.486 G2 19 74.747 G3 23 247.083 G4 27 -192.806

[0128] Fig. 14(A) is a diagram showing various aberrations when the optical system according to Example 7 is focused at infinity. Fig. 14(B) is a diagram showing various aberrations when the optical system according to Example 7 is focused at close range. From these aberration diagrams, it can be seen that the optical system according to Example 7 has excellent imaging performance, with various aberrations being well corrected not only when focused at infinity but also when focused at close range.

[0129] (Eighth Example) Example 8 will be described with reference to FIGS. 15 and 16 and Table 8. FIG. 15 shows the lens configuration of an optical system according to Example 8. The optical system OL (8) according to Example 8 is composed of, arranged along the optical axis from the object 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 positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I.

[0130] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, the second lens group G2 and the third lens group G3 constitute the middle group GM, and the fourth lens group G4 constitutes the rear group GR. Furthermore, the second lens group G2 corresponds to the first focusing lens group GF1, and the third lens group G3 corresponds to the second focusing lens group GF2.

[0131] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L11 with a convex surface facing the object side, a negative meniscus lens L12 with a convex surface facing the object side, a cemented positive lens formed by cementing together a positive meniscus lens L13 with a convex surface facing the object side and a negative meniscus lens L14 with a convex surface facing the object side, a cemented negative lens formed by cementing together a biconcave negative lens L15 and a biconvex positive lens L16, a biconvex positive lens L17, a biconvex positive lens L18, and a cemented negative lens formed by cementing together a biconcave negative lens L19 and a biconvex positive lens L110. The negative meniscus lens L12 has an aspheric lens surface facing the image plane.

[0132] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L21 and a biconvex positive lens L22.

[0133] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L31 with its convex surface facing the object side and a biconvex positive lens L32. The positive meniscus lens L31 has an aspherical lens surface facing the image side. The positive lens L32 has an aspherical lens surface facing the image side.

[0134] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L41 with its concave surface facing the object side and a negative meniscus lens L42 with its concave surface facing the object side. An image surface I is located on the image side of the fourth lens group G4.

[0135] Table 8 below lists the values ​​of the specifications of the optical system according to the eighth example.

[0136] (Table 8) [Overall specifications] f=35.000 FNO=1.230 ω=31.746 Y=21.600 TL=145.455 Bf=10.955 fA=55.625 fR=-115.422 fF1=489.379 fF2=77.454 fSa=55.625 fSr=106.986 fe=-55.441 [Lens specifications] Surface number RD nd νd 1 67.860 2.000 1.48749 70.31 2 28.552 8.759 3 56.466 1.800 1.58887 61.13 4* 37.716 3.790 5 51.569 7.504 2.00100 29.12 6 12706.656 1.500 1.49782 82.57 7 39.896 11.204 8 -34.883 1.500 1.85451 25.15 9 63.438 8.797 1.56732 42.58 10 -166.403 0.200 11 208.847 8.476 2.00069 25.46 12 -55.223 0.200 13 42.842 9.992 1.59349 67.00 14 -402.195 2.085 15 -164.696 1.500 1.69895 30.13 16 27.200 14.211 1.59319 67.90 17 -118.275 2.983 18∞ (D18) (Aperture S) 19 -41.627 1.300 1.68376 37.64 20 117.749 0.200 21 37.122 8.000 1.59349 67.00 22 -76.861 (D22) 23 32.715 5.200 1.85108 40.12 24* 46.365 4.147 25 212.737 2.500 1.77387 47.25 26* -1000.777 (D26) 27 -811.142 3.025 1.94595 17.98 28 -93.510 2.770 29 -37.711 1.500 1.73037 32.23 30 -558.335 Bf [Aspherical data] Side 4 κ=1.0000,A4=-1.76373E-06,A6=-1.17943E-09,A8=-1.59414E-12,A10=-1.08316E-15 Page 24 κ=1.0000,A4=-3.14395E-06,A6=-1.49476E-08,A8=-1.54681E-11,A10=1.13351E-13 Page 26 κ=1.0000,A4=1.94012E-05,A6=2.29617E-08,A8=1.02524E-10,A10=-2.34228E-13 [Variable Interval Data] Infinity focus Close focus f=35.000 β=-0.03333 D0 ∞ 1010.855 D18 12.903 11.498 D22 2.081 1.999 D26 4.374 5.861 Bf 10.955 10.955 [Lens group data] Group starting plane focal length G1 1 55.625 G2 19 489.379 G3 23 77.454 G4 27 -115.422

[0137] Fig. 16(A) is a diagram showing various aberrations when the optical system according to Example 8 is focused at infinity. Fig. 16(B) is a diagram showing various aberrations when the optical system according to Example 8 is focused at a close distance. From these aberration diagrams, it can be seen that the optical system according to Example 8 has excellent imaging performance, with various aberrations being well corrected not only when focused at infinity but also when focused at a close distance.

[0138] Next, the table of [Values ​​Corresponding to Conditional Expressions] is shown below: This table shows the values ​​corresponding to each of the conditional expressions (1) to (11) for all the examples (Examples 1 to 8). Condition (1) 0.01 <fF2 / fF1<10.00 Condition (2) 0.50 <Y / Bf<5.00 Condition (3) 0.05 <fSr / fSa<4.00 Condition (4) 0.05 <fF2 / fA<8.00 Conditional expression (5) 0.10<(-fR) / fF2<8.00 Condition (6) 0.02 <fA / fF1<4.00 Condition (7) 0.10 <fF1 / (-fR)<8.00 Condition (8) 0.10 <fA / (-fR)<4.00 Condition (9) 1.00 <f / Bf<8.00 Condition (10) 0.50 <TL / f<7.00 Condition (11) 0.10 <fe / fR<0.90

[0139] [Conditional Expression Corresponding Values] (First to Fourth Examples) Conditional Expression 1st Example 2nd Example 3rd Example 4th Example (1) 0.285 0.301 0.506 0.156 (2) 1.682 1.768 1.681 1.894 (3) 0.268 0.314 0.221 1.447 (4) 0.277 0.296 0.288 1.280 (5) 1.649 1.519 2.045 2.020 (6) 1.029 1.018 1.758 0.122 (7) 2.126 2.184 0.966 3.168 (8) 2.188 2.224 1.699 0.387 (9) 2.976 4.004 2.976 2.994 (10) 2.321 1.903 2.235 4.241 (11) 0.696 6.125 0.536 0.337 [Conditional Expression Corresponding Values] (Fifth to Eighth Examples) Conditional Expression 5th Example 6th Example 7th Example 8th Example (1) 0.111 0.836 3.306 0.158 (2) 1.894 1.894 1.894 1.981 (3) 1.231 0.812 1.028 1.923 (4) 1.074 0.770 3.505 1.392 (5) 2.370 1.038 0.780 1.490 (6) 0.104 1.085 0.943 0.114 (7) 3.790 1.152 0.388 4.240 (8) 0.393 1.251 0.366 0.482 (9) 2.994 2.994 2.994 3.195 (10) 4.241 4.532 4.591 4.156 (11) 0.339 0.445 0.206 0.480

[0140] According to each of the above embodiments, it is possible to realize an optical system that is small in size, yet bright and has good optical performance.

[0141] The above-described examples are merely illustrative examples of the present invention, and the present invention is not limited to these.

[0142] The following contents can be appropriately adopted within the scope that does not impair the optical performance of the optical system of this embodiment.

[0143] Although a four-group configuration has been shown as an example of the optical system of this embodiment, the present application is not limited to this, and optical systems with other group configurations (for example, five groups, six groups, seven groups, etc.) can also be configured. Specifically, a lens or lens group may be added to the optical system of this embodiment closest to the object or closest to the image plane. A lens or lens group may be added between the first focusing lens group and the second focusing lens group in the intermediate group of the optical system of this embodiment. Note that a lens group refers to a portion having at least one lens separated by an air gap that changes during focusing.

[0144] The lens group or partial lens group may be moved so as to have a component in a direction perpendicular to the optical axis, or may be rotated (oscillated) in a plane including the optical axis, to serve as an image stabilization lens group that corrects image blur caused by camera shake.

[0145] The lens surface may be spherical, flat, or aspherical. Spherical or flat lens surfaces are preferred because they facilitate lens processing and assembly adjustment, and prevent degradation of optical performance due to errors in processing and assembly adjustment. Furthermore, they are preferred because they minimize degradation of imaging performance even when the image plane is misaligned.

[0146] If the lens surface is aspherical, the aspherical surface may be any of the following: a ground aspherical surface, a glass-molded aspherical surface in which glass is molded into an aspherical shape, or a hybrid aspherical surface in which a resin is formed into an aspherical shape on the surface of glass. The lens surface may also be a diffractive surface, or the lens may be a gradient index lens (GRIN lens) or a plastic lens.

[0147] The aperture diaphragm is preferably located between the first lens group constituting the front group and the second lens group constituting the intermediate group, but the lens frame may serve that role instead of providing a member as an aperture diaphragm.Also, the first focusing lens group may be located opposite the image plane side of the aperture diaphragm.

[0148] Each lens surface may be coated with an anti-reflection coating that has high transmittance over a wide wavelength range in order to reduce flare and ghosting and achieve high-contrast optical performance. [Explanation of symbols]

[0149] G1 First lens group G2 Second lens group G3 3rd lens group G4 4th lens group I Image plane S Aperture stop

Claims

[Claim 1] It consists of a front group, an intermediate group, and a rear group, arranged in that order from the object side along the optical axis, the intermediate group comprises, arranged in order from the object side along the optical axis, a first focusing lens group having positive refractive power and a second focusing lens group having positive refractive power; During focusing, the first focusing lens group and the second focusing lens group move along the optical axis on different trajectories, and the front group and the rear group are fixed with respect to an image plane; the rear group has a negative lens arranged closest to the image plane, An optical system that satisfies the following condition: 0.01<fF2 / fF1<10.00 0.50<Y / Bf<5.00 where fF1 is the focal length of the first focusing lens group fF2: focal length of the second focusing lens group Y: image height of the optical system Bf: back focus of the optical system

Images