Optical Systems and Optical Instruments

Abstract

To provide an optical system which is compact and yet offers good optical performance.SOLUTION: An optical system OL provided herein comprises a first lens group G1 having positive refractive power, an aperture stop S, and a succeeding group GR arranged in order from the object side along an optical axis, the succeeding group GR comprising a first focusing lens group GF1 configured to move along the optical axis when focusing, and a second focusing lens group GF2 located on the image side of the first focusing lens group GF1 and configured to move along the optical axis when focusing. The optical system satisfies the following conditional expression: 0.03<D1 / TL<0.25, where D1 represents an axial distance from a lens surface of the first lens group G1 on the most object side to a lens surface thereof on the most image side, and TL represents a total length of the optical system OL.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system. and optical equipment Regarding. [Background technology]

[0002] Conventionally, compact, single-focus optical systems having a wide angle of view have been proposed (see, for example, Patent Document 1). In such optical systems, the overall length is long compared to the focal length of the optical system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-190742 Summary of the Invention

[0005] No. 1 The optical system according to the present invention comprises, arranged in order from the object side along an optical axis, a first lens group having positive refractive power, a second lens group having positive refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power. It consists of During focusing, the first lens group is fixed relative to the image plane, and the spacing between adjacent lens groups changes. No. 2 The optical system according to the present invention comprises, arranged in order from the object side along an optical axis, a first lens group having positive refractive power, a second lens group having positive refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power. It consists of During focusing, the first lens group is fixed relative to the image plane, and the intervals between adjacent lens groups change, and the following conditional expression is satisfied: 0.03 <D1 / TL<0.25 where D1 is the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the first lens group. TL: total length of the optical system

[0006] ThirdThe optical system according to the present invention comprises, arranged in order from the object side along an optical axis, a first lens group having positive refractive power, a second lens group having positive refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power. It consists of , when focusing, The spacing between adjacent lens groups changes, The second lens group and the third lens group move along the optical axis and satisfy the following conditional expression: 0.03 <D1 / TL<0.25 where D1 is the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the first lens group. TL: total length of the optical system

[0007] An optical device according to the present invention includes the optical system described above. [Brief explanation of the drawings]

[0011] [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 on infinity and when focused on the shortest object 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 the shortest object 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 on infinity and when focused on the shortest object 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 on infinity and when focused on the shortest object distance, respectively. [Figure 9] FIG. 1 is a diagram showing the configuration of a camera including an optical system according to each embodiment. [Figure 10] 4 is a flowchart showing a method for manufacturing the optical system according to the first embodiment. [Figure 11] 10 is a flowchart showing a method for manufacturing an optical system according to a second embodiment. [Figure 12] 10 is a flowchart showing a method for manufacturing an optical system according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present invention will be described below. First, a camera (optical device) equipped with an optical system according to each embodiment will be described with reference to FIG. 9. As shown in FIG. 9, 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.

[0013] Light from the subject is collected by the optical system OL of the photographic 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 liquid crystal screen 5 in response to a user's operation. This camera can also be used as a mirrorless camera or a single-lens reflex camera with a quick-return mirror. 9 is a schematic illustration of an optical system, and the lens configuration of the optical system OL is not limited to this configuration.

[0014] Next, an optical system according to a first embodiment will be described. As shown in FIG. 1, an optical system OL(1) as an example of the optical system OL according to the first embodiment is configured to include, in order from the object side along the optical axis, a first lens group G1 having positive refractive power, an aperture stop S, and a subsequent lens group GR. The subsequent lens group GR is configured to include a first focusing lens group GF1 that moves along the optical axis during focusing, and a second focusing lens group GF2 that is disposed closer to the image than the first focusing lens group GF1 and moves along the optical axis during focusing. It is desirable that, during focusing, the first focusing lens group GF1 and the second focusing lens group GF2 move along the optical axis by different amounts of movement.

[0015] With the above-described configuration, the optical system OL according to the first embodiment satisfies the following conditional expression (1). 0.03 <D1 / TL<0.25 ···(1) where D1 is the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the first lens group G1. TL: Total length of optical system OL

[0016] According to the first embodiment, it is possible to obtain an optical system having a short overall length relative to the focal length of the optical system, and an optical device including this optical system, which has good optical performance despite being small in size. The optical system OL according to the first 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.

[0017] Conditional expression (1) defines an appropriate relationship between the axial distance from the lens surface closest to the object to the lens surface closest to the image in the first lens group G1 and the overall length of the optical system OL. By satisfying conditional expression (1), it is possible to optimize the exit pupil position relative to the image plane (image sensor) while miniaturizing the optical system.

[0018] If the corresponding value of conditional expression (1) falls below the lower limit, the first lens group G1 becomes too thin, making it difficult to correct chromatic aberration and astigmatic difference. Furthermore, the edge and center thicknesses of the lenses constituting the first lens group G1 become too thin, making lens manufacturing difficult. By setting the lower limit of conditional expression (1) to 0.05, or even 0.07, the effects of this embodiment can be further ensured.

[0019] If the corresponding value of conditional expression (1) exceeds the upper limit, it becomes difficult to move the exit pupil position away from the image plane (image sensor). If an attempt is made to move the exit pupil position away from the image plane (image sensor), it becomes difficult to correct field curvature. By setting the upper limit of conditional expression (1) to 0.22, or even 0.20, the effect of this embodiment can be further ensured.

[0020] In the optical system OL according to the first embodiment, the subsequent group GR preferably includes, in order from the object side along the optical axis, a second lens group G2 having positive refractive power and a third lens group G3 having positive refractive power, the second lens group G2 being the first focusing lens group GF1 and the third lens group G3 being the second focusing lens group GF2. Furthermore, the subsequent group GR preferably includes a fourth lens group G4 having negative refractive power arranged next to the third lens group G3 on the image side. This reduces the overall length of the optical system relative to its focal length, resulting in a compact optical system with excellent optical performance.

[0021] Next, an optical system according to a second embodiment will be described. As shown in FIG. 1, an optical system OL(1) as an example of the optical system OL according to the second embodiment includes, arranged in order from the object side along the optical axis, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. When focusing, the distance between adjacent lens groups changes.

[0022] According to the second embodiment, it is possible to obtain an optical system having a short overall length relative to the focal length of the optical system, and an optical device including this optical system that is small yet has good optical performance. The optical system OL according to the second 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. It is desirable that the optical system OL according to the second embodiment has an aperture stop S disposed between the first lens group G1 and the second lens group G2.

[0023] It is desirable that the optical system OL according to the second embodiment satisfy the above-mentioned conditional expression (1). By satisfying conditional expression (1), it is possible to optimize the exit pupil position relative to the image plane (image sensor) while miniaturizing the optical system, as in the case of the first embodiment. Furthermore, by setting the lower limit of conditional expression (1) to 0.05, or even 0.07, the effects of this embodiment can be made more certain. By setting the upper limit of conditional expression (1) to 0.22, or even 0.20, the effects of this embodiment can be made more certain.

[0024] Next, an optical system according to a third embodiment will be described. As shown in FIG. 1, an optical system OL(1) as an example of the optical system OL according to the third embodiment is configured to include, arranged in order from the object side along the optical axis, 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. During focusing, the second lens group G2 and the third lens group G3 move along the optical axis. Note that, during focusing, it is desirable that the spacing between adjacent lens groups change.

[0025] With the above configuration, the optical system OL according to the third embodiment satisfies the above-mentioned conditional expression (1). According to the third embodiment, the overall length is short relative to the focal length of the optical system, making it possible to obtain an optical system that is compact yet has good optical performance, and an optical apparatus equipped with this optical system. The optical system OL according to the third 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. It is desirable that the optical system OL according to the third embodiment has an aperture stop S disposed between the first lens group G1 and the second lens group G2.

[0026] Furthermore, by satisfying conditional expression (1), it is possible to optimize the exit pupil position relative to the image plane (image sensor) while miniaturizing the optical system, as in the case of the first embodiment. Furthermore, by setting the lower limit of conditional expression (1) to 0.05, or even 0.07, it is possible to further ensure the effects of this embodiment. By setting the upper limit of conditional expression (1) to 0.22, or even 0.20, it is possible to further ensure the effects of this embodiment.

[0027] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (2). 1.20<(-f4) / f<2.00 (2) However, f4: focal length of the fourth lens group G4 f: focal length of optical system OL

[0028] Conditional expression (2) defines an appropriate range for the refractive power of the fourth lens group G4. By satisfying conditional expression (2), lateral chromatic aberration, distortion, and field curvature can be effectively corrected.

[0029] If the corresponding value of conditional expression (2) falls below the lower limit, the refractive power of the fourth lens group G4 becomes too strong, making it difficult to correct chromatic aberration of magnification and distortion. Also, it becomes difficult to move the exit pupil position farther from the image plane (image sensor). If the lower limit of conditional expression (2) is set to 1.40, or even 1. By setting it to .50, the effects of each embodiment can be more reliably achieved.

[0030] If the corresponding value of conditional expression (2) exceeds the upper limit, the refractive power of the fourth lens group G4 becomes too weak, making it difficult to correct field curvature. By setting the upper limit of conditional expression (2) to 1.85, or even 1.80, the effects of each embodiment can be further ensured.

[0031] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (3). 1.10<β4<1.40 (3) However, β4: Lateral magnification of the fourth lens group G4 when focusing at infinity

[0032] Conditional expression (3) defines an appropriate range for the lateral magnification of the fourth lens group G4. By satisfying conditional expression (3), it is possible to obtain good optical performance while miniaturizing the optical system.

[0033] If the corresponding value of conditional expression (3) falls below the lower limit, the optical system becomes large and it becomes difficult to correct the curvature of field. By setting the lower limit of conditional expression (3) to 1.17, the effects of each embodiment can be more reliably achieved.

[0034] If the corresponding value of conditional expression (3) exceeds the upper limit, it becomes difficult to correct curvature of field and distortion. By setting the upper limit of conditional expression (3) to 1.35, the effects of each embodiment can be more reliably achieved.

[0035] In the optical systems OL according to the first to third embodiments, it is desirable that the fourth lens group G4 is made up of one negative lens and satisfies the following conditional expression (4). 28.0<νd41<45.0 (4) where νd41 is the Abbe number of the negative lens in the fourth lens group G4 based on the d-line

[0036] Conditional expression (4) defines an appropriate range for the Abbe number of the negative lens that constitutes the fourth lens group G4. By satisfying conditional expression (4), lateral chromatic aberration can be effectively corrected.

[0037] If the corresponding value of conditional expression (4) falls below the lower limit, lateral chromatic aberration will be overcorrected. By setting the lower limit of conditional expression (4) to 30.0, or even 32.0, the effects of each embodiment can be further ensured.

[0038] If the corresponding value of conditional expression (4) exceeds the upper limit, correction of lateral chromatic aberration becomes insufficient. By setting the upper limit of conditional expression (4) to 43.0, or even 41.0, the effects of each embodiment can be further ensured.

[0039] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (5). 0.50 <f2 / f3<2.00 ···(5) However, f2 is the focal length of the second lens group G2. f3: Focal length of the third lens group G3

[0040] Conditional expression (5) defines an appropriate relationship between the focal length of the second lens group G2 and the focal length of the third lens group G3. By satisfying conditional expression (5), astigmatic difference and curvature of field can be effectively corrected.

[0041] If the corresponding value of conditional expression (5) falls below the lower limit, the refractive power of the third lens group G3 becomes too weak, making it difficult to correct astigmatic difference. By setting the lower limit of conditional expression (5) to 0.60, or even 0.70, the effects of each embodiment can be further ensured.

[0042] If the corresponding value of conditional expression (5) exceeds the upper limit, the refractive power of the third lens group G3 becomes too strong, making it difficult to correct curvature of field. By setting the upper limit of conditional expression (5) to 1.90, or even 1.80, the effects of each embodiment can be further ensured.

[0043] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (6). 0.04 <d23 / TL<0.11 ···(6) where d23 is the distance on the optical axis between the second lens group G2 and the third lens group G3 when focusing at infinity. TL: Total length of optical system OL

[0044] Conditional expression (6) defines an appropriate relationship between the axial distance between the second lens group G2 and the third lens group G3 and the overall length of the optical system OL. By satisfying conditional expression (6), the movement space required for focusing for each lens group is ensured, and good optical performance can be obtained even when focusing at close range.

[0045] If the value corresponding to conditional expression (6) falls below the lower limit, the movement space required for focusing of each lens group will be insufficient, and it will become difficult to correct astigmatism when focusing at close distances. By setting the lower limit of conditional expression (6) to 0.05, the effects of each embodiment can be more reliably achieved.

[0046] If the value corresponding to conditional expression (6) exceeds the upper limit, it becomes difficult to correct coma aberration when focusing at close distances. By setting the upper limit of conditional expression (6) to 0.10, the effects of each embodiment can be more reliably achieved.

[0047] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (7). 0.60 <d23 / d12<1.00 ···(7) where d23 is the distance on the optical axis between the second lens group G2 and the third lens group G3 when focusing at infinity. d12: The distance on the optical axis between the first lens group G1 and the second lens group G2 when focusing at infinity

[0048] Conditional expression (7) defines an appropriate relationship between the axial distance between the second lens group G2 and the third lens group G3 and the axial distance between the first lens group G1 and the second lens group G2. By satisfying conditional expression (7), the movement space required for focusing for each lens group is ensured, and good optical performance can be obtained even when focusing at close range.

[0049] If the value corresponding to conditional expression (7) falls below the lower limit, it becomes difficult to correct astigmatism when focusing at close distances. By setting the lower limit of conditional expression (7) to 0.67, the effects of each embodiment can be more reliably achieved.

[0050] If the value corresponding to conditional expression (7) exceeds the upper limit, it becomes difficult to correct coma when focusing at close distances. By setting the upper limit of conditional expression (7) to 0.92, the effects of each embodiment can be more reliably achieved.

[0051] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (8). 0.10<β2 / β3<0.90 (8) However, β2 is the lateral magnification of the second lens group G2 when focusing at infinity. β3: Lateral magnification of the third lens group G3 when focusing at infinity

[0052] Conditional expression (8) defines an appropriate relationship between the lateral magnification of the second lens group G2 and the lateral magnification of the third lens group G3. By satisfying conditional expression (8), good optical performance can be obtained even when focusing at close distances.

[0053] If the value corresponding to conditional expression (8) falls below the lower limit, it becomes difficult to correct astigmatism when focusing at close distances. By setting the lower limit of conditional expression (8) to 0.18, the effects of each embodiment can be more reliably achieved.

[0054] If the value corresponding to conditional expression (8) exceeds the upper limit, it becomes difficult to correct coma aberration when focusing at close distances. By setting the upper limit of conditional expression (8) to 0.80, the effects of each embodiment can be more reliably achieved.

[0055] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (9). 0.015<{β2+(1 / β2)} -2 <0.170 (9) However, β2 is the lateral magnification of the second lens group G2 when focusing at infinity.

[0056] Conditional expression (9) defines an appropriate range for the lateral magnification of the second lens group G2. By satisfying conditional expression (9), the amount of movement of the second lens group G2 from infinity focusing to close-up focusing can be reduced, making it possible to reduce the size of the lens and obtain good optical performance.

[0057] If the corresponding value of conditional expression (9) falls below the lower limit, it becomes difficult to correct spherical aberration and axial chromatic aberration. By setting the lower limit of conditional expression (9) to 0.020, the effects of each embodiment can be more reliably achieved.

[0058] If the value corresponding to conditional expression (9) exceeds the upper limit, the movement amount of the second lens group when focusing from infinity to close distance becomes large, the lens becomes large, and correction of astigmatism becomes difficult. By setting the upper limit of conditional expression (9) to 0.150, the effects of each embodiment can be more reliably achieved.

[0059] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (10). 0.100<{β3+(1 / β3)} -2 <0.250 (10) However, β3 is the lateral magnification of the third lens group G3 when focusing at infinity.

[0060] Conditional expression (10) defines an appropriate range for the lateral magnification of the third lens group G3. By satisfying conditional expression (10), the amount of movement of the third lens group G3 from infinity focusing to close-up focusing can be reduced, making it possible to reduce the size of the lens and obtain good optical performance.

[0061] If the corresponding value of conditional expression (10) falls below the lower limit, it becomes difficult to correct curvature of field and astigmatism. By setting the lower limit of conditional expression (10) to 0.160, the effects of each embodiment can be more reliably achieved.

[0062] If the value of conditional expression (10) exceeds the upper limit, the amount of movement of the third lens group from the infinity focusing state to the closest distance focusing state becomes large, the lens becomes large, and it becomes difficult to correct astigmatism. By setting the upper limit of conditional expression (10) to 0.230, This makes it possible to ensure the effectiveness of the state.

[0063] In the optical systems OL according to the first to third embodiments, the second lens group G2 preferably comprises, in order from the object side along the optical axis, a first positive lens, a first negative lens, a second negative lens, and a second positive lens. The second lens group G2 preferably comprises, in order from the object side along the optical axis, a positive lens component comprising a first positive lens and a first negative lens, a second negative lens, and a second positive lens. This allows for excellent correction of axial chromatic aberration, spherical aberration, coma, astigmatic aberration, etc., while also appropriately reducing the Petzval sum and excellent correction of field curvature.

[0064] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (11). 0.00 <N21-N22<0.40 ···(11) where N21 is the refractive index of the first positive lens in the second lens group G2 at the d-line N22: refractive index of the first negative lens in the second lens group G2 at the d-line

[0065] Conditional expression (11) defines an appropriate range for the difference in refractive index between the first positive lens and the first negative lens in the second lens group G2. By satisfying conditional expression (11), it is possible to effectively correct curvature of field and spherical aberration.

[0066] If the corresponding value of conditional expression (11) falls below the lower limit, it becomes difficult to correct curvature of field. By setting the lower limit of conditional expression (11) to 0.10, or even 0.15, the effects of each embodiment can be further ensured.

[0067] If the corresponding value of conditional expression (11) exceeds the upper limit, it becomes difficult to correct spherical aberration. By setting the upper limit of conditional expression (11) to 0.35, or even 0.30, the effects of each embodiment can be further ensured.

[0068] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (12). N21>1.90 (12) where N21 is the refractive index of the first positive lens in the second lens group G2 at the d-line

[0069] Conditional expression (12) defines an appropriate range for the refractive index of the first positive lens in the second lens group G2. By satisfying conditional expression (12), it is possible to reduce the Petzval sum without worsening spherical aberration and coma, and to effectively correct field curvature.

[0070] If the corresponding value of conditional expression (12) falls below the lower limit, the Petzval sum increases, making it difficult to correct the curvature of field. By setting the lower limit of conditional expression (12) to 1.95, the effects of each embodiment can be more reliably achieved.

[0071] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (13). 25.0<νd21<35.0 (13) where νd21 is the Abbe number of the first positive lens in the second lens group G2 based on the d-line

[0072] Conditional expression (13) defines an appropriate range for the Abbe number of the first positive lens in the second lens group G2. By satisfying conditional expression (13), longitudinal chromatic aberration can be corrected well.

[0073] If the corresponding value of conditional expression (13) falls below the lower limit, longitudinal chromatic aberration will be undercorrected, making it difficult to achieve good correction. By setting the lower limit of conditional expression (13) to 28.0, the effects of each embodiment can be more reliably achieved.

[0074] If the corresponding value of conditional expression (13) exceeds the upper limit, axial chromatic aberration will be overcorrected, making it difficult to achieve good correction. By setting the upper limit of conditional expression (13) to 31.0, the effects of each embodiment can be more reliably achieved.

[0075] In the optical systems OL according to the first to third embodiments, it is desirable for the third lens group G3 to have one positive lens, which makes it possible to make the optical system compact and to effectively correct field curvature.

[0076] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (14). -1.20<(R31+R32) / (R32-R31)<0.00 ···(14) where R31: paraxial radius of curvature of the object-side lens surface of the positive lens in the third lens group G3 R32: Paraxial radius of curvature of the image-side lens surface of the positive lens in the third lens group G3

[0077] Conditional expression (14) defines an appropriate range for the shape factor of the positive lens that constitutes the third lens group G3. By satisfying conditional expression (14), spherical aberration and astigmatism can be effectively corrected.

[0078] If the corresponding value of conditional expression (14) falls below the lower limit, it becomes difficult to correct spherical aberration. By setting the lower limit of conditional expression (14) to −1.05, the effects of each embodiment can be more reliably achieved.

[0079] If the corresponding value of conditional expression (14) exceeds the upper limit, it becomes difficult to correct astigmatism. By setting the upper limit of conditional expression (14) to −0.10, the effects of each embodiment can be more reliably achieved.

[0080] It is desirable that the optical systems OL according to the first to third embodiments satisfy the following conditional expression (15). 0.00 <f / f1<0.70 ···(15) where f is the focal length of the optical system OL f1: focal length of the first lens group G1

[0081] Condition (15) defines an appropriate range for the refractive power of the first lens group G1. By satisfying condition (15), spherical aberration, curvature of field, and astigmatic difference can be effectively corrected.

[0082] If the corresponding value of conditional expression (15) falls below the lower limit, it becomes difficult to correct spherical aberration. By setting the lower limit of conditional expression (15) to 0.10, or even 0.13, the effects of each embodiment can be further ensured.

[0083] If the corresponding value of conditional expression (15) exceeds the upper limit, it becomes difficult to correct curvature of field and astigmatic difference. By setting the upper limit of conditional expression (15) to 0.50, or even 0.35, the effects of each embodiment can be further ensured.

[0084] In the optical systems OL according to the first to third embodiments, it is desirable that the first lens group G1 is made up of at least two lenses. This makes it possible to effectively correct axial chromatic aberration, spherical aberration, and coma. can be corrected to

[0085] In the optical systems OL according to the first to third embodiments, it is desirable that the first lens group G1 has a negative lens positioned closest to the object, which allows for good correction of astigmatism.

[0086] Next, a manufacturing method of the optical system OL according to the first embodiment will be outlined with reference to FIG. 10. First, a first lens group G1 having positive refractive power, an aperture stop S, and a subsequent lens group GR are arranged, in order from the object side along the optical axis (Step ST1). Next, a first focusing lens group GF1 that moves along the optical axis during focusing, and a second focusing lens group located on the image side of the first focusing lens group GF1 and that moves along the optical axis during focusing, are arranged in the subsequent lens group GR (Step ST2). Then, the lenses are arranged in the lens barrel so as to satisfy at least the above-mentioned conditional expression (1) (Step ST3). This manufacturing method shortens the overall length relative to the focal length of the optical system, making it possible to manufacture an optical system that is compact yet has good optical performance.

[0087] Next, a manufacturing method of the optical system OL according to the second embodiment will be outlined with reference to FIG. 11. First, 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 are arranged in order from the object side along the optical axis (step ST11). Then, the lenses are arranged in the lens barrel so that the spacing between adjacent lens groups changes during focusing (step ST12). This manufacturing method shortens the overall length relative to the focal length of the optical system, making it possible to manufacture an optical system that is compact yet has good optical performance.

[0088] Next, a manufacturing method of the optical system OL according to the third embodiment will be outlined with reference to FIG. 12. First, 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 are arranged, in order from the object side along the optical axis (step ST21). Next, the second lens group G2 and the third lens group G3 are configured to move along the optical axis during focusing (step ST22). Then, the lenses are arranged in the lens barrel so as to satisfy at least the above-mentioned conditional expression (1) (step ST23). This manufacturing method shortens the overall length relative to the focal length of the optical system, making it possible to manufacture an optical system that is compact yet has good optical performance. [Example]

[0089] Optical systems OL according to examples of each embodiment will be described below with reference to the drawings. Figures 1, 3, 5, and 7 are cross-sectional views showing the configuration and refractive power distribution of optical systems OL {OL(1) to OL(4)} according to examples 1 to 4. In the cross-sectional views of the optical systems OL(1) to OL(4) according to examples 1 to 4, arrows indicate the direction of movement of each lens group along the optical axis when focusing from infinity to a close-distance object.

[0090] 1, 3, 5, and 7, 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 group, 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.

[0091] Tables 1 to 4 are shown below, where Table 1 shows the data of each element in the first embodiment, Table 2 in the second embodiment, Table 3 in the third embodiment, and Table 4 in the fourth embodiment. The d-line (wavelength λ=587.6 nm) and g-line (wavelength λ=435.8 nm) were selected as the targets for calculating the properties.

[0092] 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 (maximum angle of incidence, in degrees), and Y is the image height. TL is the distance from the frontmost lens surface to the last lens surface on the optical axis plus BF, and BF is the distance from the last lens surface on the optical axis to the image plane I (back focus). Also, BFa is the air-equivalent back focus length. Also in the [Overall Specifications] table, β2 is the lateral magnification of the second lens group when focused at infinity. β3 is the lateral magnification of the third lens group when focused at infinity. β4 is the lateral magnification of the fourth lens group when focused at infinity.

[0093] In the [Lens Specifications] table, the surface number indicates the order of the optical surfaces from the object side along the direction of light travel, R is the radius of curvature of each optical surface (a surface whose center of curvature is located on the image side is 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 surface), nd is the refractive index of the material of the optical element with respect to the d-line, and νd is the Abbe number based on the d-line of the material of the optical element. The "∞" in the radius of curvature indicates a plane 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, In such cases, an * is added to the surface number, and the paraxial radius of curvature is shown in the radius of curvature R column.

[0094] In the [Aspherical Data] table, the shape of the aspherical surface shown in [Lens Specifications] is shown by the following formula (A). Here, y is the height in the direction perpendicular to the optical axis, X(y) is the distance (amount of sag) along the optical axis from the tangent plane of the apex of the aspherical surface at height y to the aspherical surface, 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" is the ratio of "×10 -n For example, 1.234E-05 = 1.234 x 10 -5 The second-order aspherical coefficient A2 is 0, and is therefore omitted.

[0095] X(y)=(y 2 / R) / {1+(1-κ×y2 / R 2 ) 1 / 2}+A4×y 4 +A6×y 6 +A8×y 8 +A10×y 10 +A12×y 12 +A14×y 14 (A)

[0096] The [Variable Distance Data] table shows the surface spacing for surface number i, where the surface spacing in the [Lens Specifications] table is (Di). In the [Variable Distance Data] table, f indicates the focal length of the entire lens system, and β indicates the shooting magnification. D0 indicates the distance from the object to the lens surface in the optical system that is closest to the object. Note that infinity indicates when focusing on an object at infinity, and close distance indicates when focusing on a close object (object with the shortest shooting distance).

[0097] The [Lens Group Data] table shows the starting surface (the surface closest to the object) and focal length of each lens group.

[0098] 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.

[0099] The explanation of the tables up to this point is common to all the embodiments, and duplicate explanations will be omitted below.

[0100] (First Example) The first example will be described with reference to FIGS. 1 and 2 and Table 1. FIG. 1 shows the lens configuration of the optical system according to the first example when focused at infinity. The optical system OL(1) according to the first example comprises, arranged in order from the object side along the optical axis, a first lens group G1 having positive refractive power, an aperture stop S, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power. The lens is composed of a third lens group G3 and a fourth lens group G4 with negative refractive power. When focusing from an object at infinity to a close-up object (the object at the shortest shooting distance), the second lens group G2 and the third lens group G3 move toward the object by different amounts along the optical axis, changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1, aperture stop S, and 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 that lens group, and this is the same in all of the following embodiments.

[0101] In this embodiment, the second lens group G2, the third lens group G3, and the fourth lens group G4 constitute a rear group GR having a positive refractive power as a whole. The second lens group G2 corresponds to the first focusing lens group GF1 in the rear group GR. The third lens group G3 corresponds to the second focusing lens group GF2 in the rear group GR.

[0102] The first lens group G1 is composed of, in order from the object side, a cemented lens having positive refractive power, in which a negative lens L11 and a positive lens L12 are cemented together. That is, the first lens group G1 is composed of a single lens component. The lens surface of the positive lens L12 facing the image side is aspherical.

[0103] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a cemented lens having positive refractive power, formed by cementing a first positive lens L21 and a first negative lens L22, a second negative lens L23, and a second positive lens L24. The second positive lens L24 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 second positive lens L24 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.

[0104] The third lens group G3 is composed of one positive lens element 31. The image-side lens element 31 has an aspherical lens surface.

[0105] The fourth lens group G4 is composed of one negative lens 41. An image plane I is disposed on the image side of the fourth lens group G4. A removable and interchangeable optical filter FL is disposed between the fourth lens group G4 and the image plane I. Examples of the optical filter FL that can be used include an NC filter (neutral color filter), a color filter, a polarizing filter, an ND filter (neutral density filter), an IR cut filter (infrared cut filter), and a UV cut filter (ultraviolet cut filter). The same applies to the optical filters FL described in the second to fourth embodiments described below. An image sensor (not shown) composed of a CCD, CMOS, or the like is disposed on the image plane I.

[0106] Table 1 below lists the values ​​of the specifications of the optical system according to the first example.

[0107] (Table 1) [Overall specifications] f=28.819 FNO=2.867 ω=37.317 Y=21.700 TL=50,000 Bf=0.860 Bfa=11.955 β2=0.441 β3=0.571 β4=1.266 [Lens specifications] Surface number RD nd νd Object plane ∞ 1 -60.48802 0.700 1.59270 35.27 2 11.61464 3.100 1.85135 40.13 3* 561.56916 1.000 4∞ (D4) (Aperture S) 5 35.50000 2.500 2.00100 29.12 6 -14.64116 0.700 1.72825 28.38 7 30.24772 3.950 8 -9.76003 0.900 1.84666 23.80 9 -30.93498 0.200 10 ∞ 6.300 1.77250 49.62 11 -17.91507 0.100 1.56093 36.64 12* -17.00000 (D12) 13 414.76419 5.100 1.80139 45.46 14* -27.47335 (D14) 15 -34.00000 1.100 1.67270 32.19 16 500.00000 10.040 17 ∞ 1.600 1.51680 63.88 18 ∞ BF Image plane∞ [Aspherical surface] Page 3 κ=1.00000E+00,A4=1.25556E-05,A6=1.12657E-07,A8=0.00000E+00 A10=-5.00000E-12,A12=0.00000E+00,A14=0.00000E+00 Page 12 κ=1.00000E+00,A4=2.16700E-05,A6=-5.98193E-08,A8=8.79250E-10 A10=-1.62238E-12,A12=4.08020E-15,A14=0.00000E+00 Page 14 κ=1.00000E+00,A4=1.90302E-05,A6=5.11786E-08,A8=-1.22839E-10 A10=1.54556E-13,A12=-5.38110E-17,A14=0.00000E+00 [Can change the interval データ] Unlimited long and short distances f=28.819 β=-0.196 D0 ∞ 140.000 D4 3.850 2.550 D12 4.300 1.296 D14 3.700 8.004 [Lens group data] Group starting plane focal length G1 1 90.286 G2 5 57.993 G3 13 32.318 G4 15 -47.285

[0108] FIG. 2(A) is a diagram showing various aberrations when the optical system according to Example 1 is focused at infinity. FIG. 2(B) is a diagram showing various aberrations when the optical system according to Example 1 is focused at the shortest shooting distance. In each aberration diagram when focused at infinity, FNO indicates the F-number, and Y indicates the image height. In each aberration diagram, NA indicates the numerical aperture, and Y indicates the image height. Spherical aberration diagrams indicate the F-number or numerical aperture value corresponding to the maximum aperture, astigmatism diagrams and distortion diagrams indicate the maximum image height, and coma diagrams indicate 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 astigmatism diagrams, the solid line indicates the sagittal image plane, and the dashed line indicates the meridional image plane. The same symbols as in this embodiment are used in the aberration diagrams of each embodiment shown below, and redundant explanations will be omitted.

[0109] 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 over the entire range from focusing at infinity to focusing at the shortest shooting distance.

[0110] (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 of the second example when focused at infinity. The optical system OL(2) of the second example is composed of, arranged along the optical axis from the object side, a first lens group G1 having positive refractive power, an aperture stop S, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close-up object (the object at the shortest shooting distance), the second lens group G2 and the third lens group G3 move toward the object side by different amounts along the optical axis, changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1, the aperture stop S, and the fourth lens group G4 are fixed relative to the image plane I.

[0111] In this embodiment, the second lens group G2, the third lens group G3, and the fourth lens group G4 constitute a rear group GR having a positive refractive power as a whole. The second lens group G2 corresponds to the first focusing lens group GF1 in the rear group GR. The third lens group G3 corresponds to the second focusing lens group GF2 in the rear group GR.

[0112] The first lens group G1 is composed of a negative lens L11 and a positive lens L12, arranged in this order from the object side along the optical axis.

[0113] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a cemented lens having positive refractive power, formed by cementing a first positive lens L21 and a first negative lens L22, a second negative lens L23, and a second positive lens L24. The second positive lens L24 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 second positive lens L24 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.

[0114] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a negative lens 31 and a positive lens 32. The negative lens 31 has aspherical lens surfaces on both sides.

[0115] The fourth lens group G4 is composed of one negative lens 41. An image plane I is disposed on the image side of the fourth lens group G4. A removable and replaceable optical filter FL is disposed between the fourth lens group G4 and the image plane I. An image sensor (not shown) composed of a CCD, CMOS, or the like is also disposed on the image plane I.

[0116] Table 2 below lists the values ​​of the specifications of the optical system according to the second example.

[0117] (Table 2) [Overall specifications] f=28.824 FNO=2.909 ω=38.029 Y=21.700 TL=54.610 Bf=0.860 Bfa=13.138 β2=0.163 β3=0.721 β4=1.310 [Lens specifications] Surface number RD nd νd Object plane ∞ 1 -67.65263 0.800 1.53172 48.78 2 18.07229 1.030 3 19.61204 2.300 1.80400 46.60 4∞1.000 5∞ (D5) (S aperture) 6 39.03942 3.000 2.00100 29.12 7 -14.01800 0.700 1.80518 25.45 8 44.52125 3.457 9 -11.08066 0.900 1.80809 22.74 10 -29.93301 0.150 11 ∞ 6.550 1.80400 46.60 12 -17.50329 0.140 1.56093 36.64 13* -16.27553 (D13) 14* -26.85154 2.000 1.53113 55.73 15* -28.96313 0.200 16 ∞ 4.500 1.80400 46.60 17 -36.85132 (D17) 18 -34.46648 1.200 1.64769 33.73 19 173.14403 11.223 20 ∞ 1.600 1.51680 63.88 21 ∞ BF Image plane∞ [Aspherical surface] Page 13 κ=1.00000E+00,A4=2.85655E-05,A6=-1.38279E-08,A8=5.79289E-10 A10=9.06875E-13,A12=-2.25760E-15,A14=1.33070E-17 Page 14 κ=1.00000E+00,A4=2.41081E-05,A6=9.24872E-08,A8=-6.64821E-10 A10=1.30136E-12,A12=8.89760E-16,A14=0.00000E+00 Page 15 κ=1.00000E+00,A4=3.97489E-05,A6=2.41498E-07,A8=-1.14609E-09 A10=2.49848E-12,A12=-2.3864E-15,A14=0.00000E+00 [Can change the interval データ] Infinite long and short distance f=28.824 β=-0.203 D0 ∞ 135.390 D5 4.850 3.169 D13 4.450 1.339 D17 3.700 8.492 [Lens group data] Group starting plane focal length G1 1 187.243 G2 6 34.689 G3 14 46.577 G4 18 -44.279

[0118] Fig. 4(A) is a diagram showing various aberrations of the optical system according to Example 2 when focused at infinity. Fig. 4(B) is a diagram showing various aberrations of the optical system according to Example 2 when focused at the minimum shooting distance. From these aberration diagrams, it can be seen that the optical system according to Example 2 has excellent imaging performance, with various aberrations being well corrected across the entire range from focusing at infinity to focusing at the minimum shooting distance.

[0119] (Third Example) Example 3 will be described with reference to FIGS. 5-6 and Table 3. FIG. 5 shows the lens configuration of the optical system of Example 3 when focused at infinity. The optical system OL(3) of Example 3 is composed of, arranged along the optical axis from the object side, a first lens group G1 having positive refractive power, an aperture stop S, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close-up object (the object at the shortest shooting distance), the second lens group G2 and the third lens group G3 move toward the object side by different amounts along the optical axis, changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1, aperture stop S, and fourth lens group G4 are fixed relative to the image plane I.

[0120] In this embodiment, the second lens group G2, the third lens group G3, and the fourth lens group G4 constitute a rear group GR having a positive refractive power as a whole. The second lens group G2 corresponds to the first focusing lens group GF1 in the rear group GR. The third lens group G3 corresponds to the second focusing lens group GF2 in the rear group GR.

[0121] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a first negative lens L11, a second negative lens L12, and a cemented lens having positive refractive power formed by cementing a positive lens L13 and a third negative lens L14. Both lens surfaces of the second negative lens L12 are aspherical.

[0122] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a cemented lens having positive refractive power formed by cementing a first positive lens L21 and a first negative lens L22, a second negative lens L23, and a second positive lens L24. The lens surface of the second positive lens L24 facing the image side is aspherical.

[0123] The third lens group G3 is composed of one positive lens element 31. The image-side lens element 31 has an aspherical lens surface.

[0124] The fourth lens group G4 is composed of one negative lens 41. An image plane I is disposed on the image side of the fourth lens group G4. A removable and replaceable optical filter FL is disposed between the fourth lens group G4 and the image plane I. An image sensor (not shown) composed of a CCD, CMOS, or the like is also disposed on the image plane I.

[0125] Table 3 below lists the values ​​of the specifications of the optical system according to the third example.

[0126] (Table 3) [Overall specifications] f=28.805 FNO=2.067 ω=37.270 Y=21.700 TL=59,500 Bf=0.800 Bfa=11.855 β2=0.427 β3=0.565 β4=1.245 [Lens specifications] Surface number RD nd νd Object plane ∞ 1 40.41078 1.000 1.48749 70.31 2 16.22403 3.600 3* -70.24185 1.300 1.82115 24.06 4* 148.16663 0.200 5 20.51937 4.000 1.88300 40.66 6 -32.92528 1.100 1.59270 35.27 7 65.09547 2.000 8∞ (D8) (S aperture) 9 44.75110 3.300 2.00100 29.12 10 -20.22294 0.800 1.75520 27.57 11 61.74745 4.400 12 -12.31509 0.900 1.84666 23.80 13 -49.27479 0.200 14 -1190.54970 6.300 1.76802 49.23 15* -19.49783 (D15) 16 76.50071 4.700 1.77377 47.18 17* -42.68869 (D17) 18 -34.74758 1.200 1.64769 33.73 19 714.84773 10.000 20 ∞ 1.600 1.51680 63.88 21∞BF Image plane ∞ [Aspherical data] 3rd page κ=1.00000E+00,A4=-3.81302E-05,A6=1.79518E-07,A8=0.00000E+00 A10=0.00000E+00,A12=0.00000E+00,A14=0.00000E+00 Side 4 κ=1.00000E+00,A4=-2.32360E-05,A6=2.17814E-07,A8=2.83578E-10 A10=0.00000E+00,A12=0.00000E+00,A14=0.00000E+00 Page 15 κ=1.00000E+00,A4=-3.48371E-06,A6=1.39242E-08,A8=1.83753E-10 A10=2.97697E-13,A12=0.00000E+00,A14=0.00000E+00 Page 17 κ=1.00000E+00,A4=2.81807E-05,A6=-1.57952E-08,A8=4.54301E-11 A10=-1.20045E-13,A12=0.00000E+00,A14=0.00000E+00 [Variable Interval Data] Infinity Near distance f=28.805 β=-0.124 D0 ∞ 220.500 D8 4.000 3.015 D15 3.500 1.629 D17 4.600 7.456 [Lens group data] Group starting plane focal length G1 1 95.848 G2 9 63.426 G3 16 36.030 G4 18 -51.129

[0127] Fig. 6(A) is a diagram showing various aberrations of the optical system according to Example 3 when focused at infinity. Fig. 6(B) is a diagram showing various aberrations of the optical system according to Example 3 when focused at the minimum shooting distance. From the diagrams of various aberrations, it can be seen that the optical system according to Example 3 has excellent imaging performance, with various aberrations being well corrected across the entire range from focusing at infinity to focusing at the minimum shooting distance.

[0128] (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 of Example 4 when focused at infinity. The optical system OL(4) of Example 4 is composed of, arranged along the optical axis from the object side, a first lens group G1 having positive refractive power, an aperture stop S, a second lens group G2 having positive refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing from an object at infinity to a close-up object (the object at the shortest shooting distance), the second lens group G2 and the third lens group G3 move toward the object side by different amounts along the optical axis, changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1, aperture stop S, and fourth lens group G4 are fixed relative to the image plane I.

[0129] In this embodiment, the second lens group G2, the third lens group G3, and the fourth lens group G4 constitute a rear group GR having a positive refractive power as a whole. The second lens group G2 corresponds to the first focusing lens group GF1 in the rear group GR. The third lens group G3 corresponds to the second focusing lens group GF2 in the rear group GR.

[0130] The first lens group G1 is composed of a negative lens L11 and a positive lens L12, arranged in order from the object side along the optical axis. The positive lens L12 is a hybrid lens composed of a glass lens body with a resin layer provided on the image side surface. The image side surface of the resin layer is aspherical, and the positive lens L12 is a hybrid aspherical lens. In the [Lens Specifications] described below, surface number 3 indicates the object side surface of the lens body, surface number 4 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 5 indicates the image side surface of the resin layer.

[0131] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a cemented lens having positive refractive power formed by cementing a first positive lens L21 and a first negative lens L22, a second negative lens L23, and a second positive lens L24. The lens surface of the second positive lens L24 facing the image side is aspherical.

[0132] The third lens group G3 is composed of one positive lens element 31. The image-side lens element 31 has an aspherical lens surface.

[0133] The fourth lens group G4 is composed of one negative lens 41. An image plane I is disposed on the image side of the fourth lens group G4. A removable and replaceable optical filter FL is disposed between the fourth lens group G4 and the image plane I. An image sensor (not shown) composed of a CCD, CMOS, or the like is also disposed on the image plane I.

[0134] Table 4 below lists the values ​​of the specifications of the optical system according to the fourth example.

[0135] (Table 4) [Overall specifications] f=28.802 FNO=2.861 ω=37.036 Y=21.700 TL=50.042 Bf=0.860 Bfa=11.697 β2=0.406 β3=0.679 β4=1.248 [Lens specifications] Surface number RD nd νd Object plane ∞ 1 -33.60557 0.900 1.59270 35.27 2 24.37821 0.300 3 21.36640 2.400 1.84850 43.79 4 -64.21743 0.100 1.56093 36.64 5* -64.21743 1.000 6∞ (D6) (Aperture S) 7 48.57194 2.700 2.00100 29.12 8 -16.54854 0.700 1.71736 29.57 9 50.38696 3.800 10 -11.12244 1.000 1.80809 22.74 11 -43.70934 0.200 12 -628.97652 7.000 1.75501 51.15 13* -16.56020 (D13) 14 326.40430 3.900 1.76802 49.23 15* -38.59856 (D15) 16 -23.79495 1.000 1.58144 40.98 17 -129.23419 9.782 18 ∞ 1.600 1.51680 63.88 19 ∞ BF Image plane∞ [Aspherical surface] Page 5 κ=5.65120E+00,A4=1.32957E-05,A6=3.71890E-08,A8=0.00000E+00 A10=0.00000E+00,A12=0.00000E+00,A14=0.00000E+00 Page 13 κ=-5.67700E-01,A4=-1.05001E-05,A6=-8.81582E-08,A8=4.96402E-10 A10=-7.84585E-13,A12=0.00000E+00,A14=0.00000E+00 Page 15 κ=1.00000E+00,A4=1.63200E-05,A6=5.26856E-08,A8=-1.38087E-10 A10=2.83555E-13,A12=0.00000E+00,A14=0.00000E+00 [Can change the interval データ] Unlimited long and short distances f=28.802 β=-0.199 D0 ∞ 139.958 D6 4.100 2.428 D13 4.300 0.956 D15 4.400 9.416 [Lens group data] Group starting plane focal length G1 1 83.642 G2 7 47.380 G3 14 45.152 G4 16 -50.335

[0136] Fig. 8(A) is a diagram showing various aberrations of the optical system according to Example 4 when focused at infinity. Fig. 8(B) is a diagram showing various aberrations of the optical system according to Example 4 when focused at the minimum shooting distance. From the diagrams of various aberrations, it can be seen that the optical system according to Example 4 has excellent imaging performance, with various aberrations being well corrected across the entire range from focusing at infinity to focusing at the minimum shooting distance.

[0137] 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 (15) for all the examples (Examples 1 to 4). Condition (1) 0.03 <D1 / TL<0.25 Condition (2) 1.20<(-f4) / f<2.00 Conditional expression (3) 1.10<β4<1.40 Conditional expression (4) 28.0<νd41<45.0 Condition (5) 0.50 <f2 / f3<2.00 Condition (6) 0.04 <d23 / TL<0.11 Condition (7) 0.60 <d23 / d12<1.00 Conditional expression (8) 0.10<β2 / β3<0.90 Conditional expression (9) 0.015<{β2+(1 / β2)} -2 <0.170 Conditional expression (10) 0.100<{β3+(1 / β3)} -2 <0.250 Conditional expression (11) 0.00 <N21-N22<0.40 Conditional expression (12) N21>1.90 Conditional expression (13) 25.0<νd21<35.0 Conditional expression (14) -1.20<(R31+R32) / (R32-R31)<0.00 Conditional expression (15) 0.00 <f / f1<0.70

[0138] [Conditional expression corresponding value] Conditional Expression 1st Example 2nd Example 3rd Example 4th Example (1) 0.076 0.076 0.188 0.074 (2) 1.641 1.536 1.775 1.748 (3) 1.266 1.310 1.245 1.248 (4) 32.190 33.730 33.730 40.980 (5) 1.794 0.745 1.760 1.049 (6) 0.086 0.081 0.059 0.086 (7) 0.887 0.761 0.700 0.843 (8) 0.772 0.226 0.756 0.598 (9) 0.136 0.025 0.130 0.122 (10) 0.186 0.225 0.183 0.216 (11) 0.273 0.196 0.246 0.284 (12) 2.001 2.001 2.001 2.001 (13) 29.120 29.120 29.120 29.120 (14) -0.876 -1.000 -0.284 -0.789 (15) 0.319 0.154 0.301 0.344

[0139] According to each of the above-described embodiments, the overall length of the optical system is short relative to the focal length, and an optical system that is compact yet has good optical performance can be realized.

[0140] The above-described examples are merely illustrative examples of the present invention, and the present invention is not limited to these.

[0141] The following contents can be appropriately adopted within the scope that does not impair the optical performance of the optical system of this embodiment.

[0142] 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 variable magnification optical systems with other group configurations (for example, five groups) 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. Note that a lens group refers to a portion having at least one lens separated by an air gap that changes during focusing.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] It is preferable that the aperture stop be disposed between the first lens group and the second lens group, but it is also possible to use the lens frame to fulfill that role instead of providing a member serving as an aperture stop.

[0147] 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]

[0148] G1 First lens group G2 Second lens group G3 3rd lens group G4 4th lens group I Image plane S Aperture stop

Claims

1. the lens comprises, arranged in order from the object side along the optical axis, a first lens group having positive refractive power, an aperture stop, a second lens group having positive refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power; An optical system in which, during focusing, the first lens group is fixed relative to the image plane, and the spacing between adjacent lens groups changes.

2. A lens system comprising, arranged in order from the object side along the optical axis, a first lens group having positive refractive power, a second lens group having positive refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power; An optical system in which, during focusing, the first lens group is fixed relative to the image plane, and the intervals between adjacent lens groups change, and the following condition is satisfied: 1.20<(-f4) / f<2.00 where f4 is the focal length of the fourth lens group f: focal length of the optical system

3. A lens system comprising, arranged in order from the object side along the optical axis, a first lens group having positive refractive power, a second lens group having positive refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power; An optical system in which, during focusing, the first lens group is fixed relative to the image plane, and the intervals between adjacent lens groups change, and the following condition is satisfied: 0.50<f2 / f3<2.00 where f2 is the focal length of the second lens group f3: focal length of the third lens group

4. An optical system described in any one of claims 1 to 3, which satisfies the following conditional expression. 0.03<D1 / TL<0.25 where D1 is the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the first lens group. TL: total length of the optical system

5. A lens system comprising, arranged in order from the object side along the optical axis, a first lens group having positive refractive power, a second lens group having positive refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power; During focusing, the interval between adjacent lens groups changes, and the second lens group and the third lens group move along the optical axis, An optical system that satisfies the following condition: 0.03<D1 / TL<0.25 1.20<(-f4) / f<2.00 where D1 is the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the first lens group. TL: total length of the optical system f4: focal length of the fourth lens group f: focal length of the optical system

6. A lens system comprising, arranged in order from the object side along the optical axis, a first lens group having positive refractive power, a second lens group having positive refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power; During focusing, the interval between adjacent lens groups changes, and the second lens group and the third lens group move along the optical axis, An optical system that satisfies the following condition: 0.03<D1 / TL<0.25 0.50<f2 / f3<2.00 where D1 is the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image in the first lens group. TL: total length of the optical system f2: focal length of the second lens group f3: focal length of the third lens group

7. 7. The optical system according to claim 5, wherein the first lens group is fixed relative to an image plane during focusing.

8. 8. The optical system according to claim 2, further comprising an aperture stop disposed between the first lens group and the second lens group.

9. 9. The optical system according to claim 1, wherein the following condition is satisfied: １．１０＜β４＜１．４０ where β4 is the lateral magnification of the fourth lens group when focused at infinity.

10. the fourth lens group is made up of one negative lens, 10. The optical system according to claim 1, wherein the following condition is satisfied: 28.0<νd41<45.0 where νd41 is the Abbe number of the negative lens in the fourth lens group with reference to the d-line

11. The optical system according to any one of claims 1 to 10, which satisfies the following conditional expression: 0.04<d23 / TL<0.11 where d23 is the distance on the optical axis between the second lens group and the third lens group when focused at infinity. TL: total length of the optical system

12. 12. The optical system according to claim 1, wherein the following condition is satisfied: 0.60<d23 / d12<1.00 where d23 is the distance on the optical axis between the second lens group and the third lens group when focused at infinity. d12: the distance on the optical axis between the first lens group and the second lens group when focused at infinity

13. The optical system according to any one of claims 1 to 12, which satisfies the following conditional expression: ０．１０＜β２／β３＜０．９０ where β2 is the lateral magnification of the second lens group when focused at infinity. β3: lateral magnification of the third lens group when focused at infinity

14. The optical system according to any one of claims 1 to 13, which satisfies the following conditional expression: ０．０１５＜｛β２＋（１／β２）｝ -2 ＜０．１７０ where β2 is the lateral magnification of the second lens group when focused at infinity.

15. The optical system according to any one of claims 1 to 14, which satisfies the following conditional expression: ０．１００＜｛β３＋（１／β３）｝ -2 ＜０．２５０ where β3 is the lateral magnification of the third lens group when focused at infinity.

16. The optical system according to any one of claims 1 to 15, wherein the second lens group consists of a first positive lens, a first negative lens, a second negative lens, and a second positive lens, arranged in order from the object side along the optical axis.

17. 17. The optical system according to claim 16, wherein the following condition is satisfied: 0.00<N21-N22<0.40 where N21 is the refractive index of the first positive lens in the second lens group with respect to the d-line. N22: refractive index of the first negative lens in the second lens group with respect to the d line

18. 18. The optical system according to claim 16, wherein the following condition is satisfied: N21>1.90 where N21 is the refractive index of the first positive lens in the second lens group with respect to the d-line.

19. The optical system according to any one of claims 16 to 18, which satisfies the following conditional expression: 25.0<νd21<35.0 where νd21 is the Abbe number of the first positive lens in the second lens group with respect to the d-line

20. 20. The optical system according to claim 1, wherein the third lens group includes one positive lens.

21. 21. The optical system according to claim 20, wherein the following condition is satisfied: -1.20<(R31+R32) / (R32-R31)<0.00 where R31 is the paraxial radius of curvature of the object-side lens surface of the positive lens in the third lens group. R32: paraxial radius of curvature of the image-side lens surface of the positive lens in the third lens group

22. 22. The optical system according to claim 1, wherein the following condition is satisfied: 0.00<f / f1<0.70 where f is the focal length of the optical system. f1: focal length of the first lens group

23. An optical instrument comprising the optical system according to any one of claims 1 to 22.

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