Optical system and optical apparatus

Abstract

An optical system (OL) has, in order from an object side along an optical axis, a first lens group (G1) having positive refractive power, a second lens group (G2) having negative refractive power, a third lens group (G3) having positive refractive power, and a fourth lens group (G4) having negative refractive power. When focusing is performed, the second lens group (G2) and the third lens group (G3) move along the optical axis, the interval between adjacent lens groups changes, and the optical system (OL) satisfies the following conditional expression: 0.20 < DG4 / TL < 0.40 where DG4 is the length on the optical axis of the fourth lens group (G4), and TL is the overall length of the optical system (OL) in an infinite focus state.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical system, an optical apparatus, and a manufacturing method of an optical system. BACKGROUND

[0002] Conventionally, an optical system in which a plurality of lens groups are moved along an optical axis to perform focusing has been disclosed (for example, refer to Patent Literature 1). In such an optical system, it is difficult to suppress aberration variation at the time of focusing.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2018-141888 SUMMARY

[0006] An optical system according to a first aspect of the present application includes, in order from an object side along an optical axis, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power, wherein, at the time of focusing, the second lens group and the third lens group are moved along the optical axis, the interval between adjacent lens groups changes, and the optical system satisfies the following conditional expression:

[0007] 0.20 < DG4 / TL < 0.40

[0008] wherein DG4 is the length on the optical axis of the fourth lens group,

[0009] TL is the total length of the optical system in an infinity focus state.

[0010] An optical system according to a second aspect of the present application includes, in order from an object side along an optical axis, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power, wherein, at the time of focusing, the second lens group and the third lens group are moved along the optical axis, the interval between adjacent lens groups changes, and the optical system satisfies the following conditional expression:

[0011] 3.00 < (LnR2 + LnR1) / (LnR2 - LnR1) < 5.00

[0012] wherein LnR1 is the radius of curvature of an object side lens surface in a negative lens disposed at the most image side of the optical system,

[0013] LnR2 is the radius of curvature of an image side lens surface in a negative lens disposed at the most image side of the optical system.

[0014] An optical system of the present invention includes, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power. When focusing is performed, the second lens group and the third lens group move along the optical axis, and the interval between adjacent lens groups changes. The optical system satisfies the following conditional expression:

[0015] 0.75 < f1 / (-f2) < 1.30

[0016] where f1 is the focal length of the first lens group,

[0017] f2 is the focal length of the second lens group.

[0018] An optical system of the present invention includes, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power. When focusing is performed, the second lens group and the third lens group move along the optical axis, and the interval between adjacent lens groups changes. The first lens group has a negative lens that satisfies the following conditional expression:

[0019] 1.80 < ndM1

[0020] νdM1 < 26.00

[0021] θgFM1 - (0.6415 - 0.00162 x νdM1) < 0.0120

[0022] where ndM1 is the refractive index for d line of the negative lens of the first lens group, and νdM1 is the Abbe number of the negative lens of the first lens group,

[0023] θgFM1 is the relative partial dispersion of the negative lens of the first lens group, and is defined by the following expression when ngM1 is the refractive index for g line of the negative lens of the first lens group, nFM1 is the refractive index for F line of the negative lens of the first lens group, and nCM1 is the refractive index for C line of the negative lens of the first lens group, that is, θgFM1 = (ngM1 - nFM1) / (nFM1 - nCM1).

[0024] An optical apparatus of the present invention includes the above optical system.

[0025] A manufacturing method of an optical system according to a first aspect of the present invention, the optical system including, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, wherein the lenses are arranged in a lens barrel such that, when focusing is performed, the second lens group and the third lens group move along the optical axis, the interval between adjacent lens groups changes, and the optical system satisfies the following conditional expression:

[0026] 0.20 < DG4 / TL < 0.40

[0027] wherein DG4 is the length on the optical axis of the fourth lens group,

[0028] TL is the total length of the optical system in an infinity focus state.

[0029] A manufacturing method of an optical system according to a second aspect of the present invention, the optical system including, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, wherein the lenses are arranged in a lens barrel such that, when focusing is performed, the second lens group and the third lens group move along the optical axis, the interval between adjacent lens groups changes, and the optical system satisfies the following conditional expression:

[0030] 3.00 < (LnR2+LnR1) / (LnR2-LnR1) < 5.00

[0031] wherein LnR1 is the radius of curvature of an object side lens surface in a negative lens arranged at the most image side of the optical system,

[0032] LnR2 is the radius of curvature of an image side lens surface in the negative lens arranged at the most image side of the optical system.

[0033] A manufacturing method of an optical system according to a third aspect of the present invention, the optical system including, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, wherein the lenses are arranged in a lens barrel such that, when focusing is performed, the second lens group and the third lens group move along the optical axis, the interval between adjacent lens groups changes, and the optical system satisfies the following conditional expression:

[0034] 0.75 < f1 / (-f2) < 1.30

[0035] wherein f1 is the focal length of the first lens group,

[0036] f2: The focal length of the second lens group.

[0037] The fourth invention relates to a method for manufacturing an optical system comprising a first lens group having positive optical power, a second lens group having negative optical power, a third lens group having positive optical power, and a fourth lens group having negative optical power, arranged sequentially along the optical axis from the object side. The lenses are configured within the lens barrel such that, during focusing, the second and third lens groups move along the optical axis, and the spacing between adjacent lens groups changes. The first lens group has a negative lens that satisfies the following condition:

[0038] 1.80 <ndM1

[0039] νdM1<26.00

[0040] θgFM1-(0.6415-0.00162×νdM1)<0.0120

[0041] Wherein, ndM1: the refractive index of the negative lens of the first lens group for the d-line, and νdM1: the Abbe number of the negative lens of the first lens group.

[0042] θgFM1: The relative partial dispersion of the negative lens of the first lens group, defined by the following formula when the refractive index of the negative lens of the first lens group to the g line is set as ngM1, the refractive index of the negative lens of the first lens group to the F line is set as nFM1, and the refractive index of the negative lens of the first lens group to the C line is set as nCM1, namely, θgFM1=(ngM1-nFM1) / (nFM1-nCM1). Attached Figure Description

[0043] Figure 1 This is a diagram showing the lens structure of the optical system of the first embodiment.

[0044] Figure 2 (A) Figure 2 (B) are aberration diagrams of the optical system of the first embodiment in the infinity focusing state and the closest focusing distance focusing state.

[0045] Figure 3 This is a diagram showing the lens structure of the optical system of the second embodiment.

[0046] Figure 4 (A) Figure 4 (B) are aberration diagrams of the optical system of the second embodiment in the infinity focusing state and the closest focusing distance focusing state.

[0047] Figure 5This is a diagram showing the lens structure of the optical system of the third embodiment.

[0048] Figure 6 (A) Figure 6 (B) are aberration diagrams of the optical system of the third embodiment at infinity focus and at the closest focus distance.

[0049] Figure 7 This is a diagram showing the lens structure of the optical system of the fourth embodiment.

[0050] Figure 8 (A) Figure 8 (B) are aberration diagrams of the optical system of the fourth embodiment in the infinity focusing state and the closest focusing distance focusing state.

[0051] Figure 9 This is a diagram showing the lens structure of the optical system of the fifth embodiment.

[0052] Figure 10 (A) Figure 10 (B) are aberration diagrams of the optical system of the fifth embodiment in the infinity focusing state and the closest focusing distance focusing state.

[0053] Figure 11 This is a diagram showing the structure of a camera equipped with an optical system according to various embodiments.

[0054] Figure 12 This is a flowchart illustrating the manufacturing method of the optical system according to embodiments 1 to 3.

[0055] Figure 13 This is a flowchart illustrating a method for manufacturing an optical system according to the fourth embodiment. Detailed Implementation

[0056] The preferred embodiments of the present invention will be described below. First, according to... Figure 11 A camera (optical device) having an optical system with each embodiment will be described. For example... Figure 11 As shown, the camera 1 comprises a main body 2 and a photographic lens 3 mounted on the main body 2. The main body 2 includes an image capturing element 4, a main control unit (not shown) for controlling the operation of the digital camera, and an LCD screen 5. The photographic lens 3 includes an optical system OL composed of multiple lens groups and a lens position control mechanism (not shown) for controlling the position of each lens group. The lens position control mechanism consists of a sensor for detecting the position of the lens groups, a motor for moving the lens groups back and forth along the optical axis, and a control circuit for driving the motor.

[0057] Light from the subject is condensed by the optical system OL of the photographing lens 3 to reach the image plane I of the imaging element 4. The light from the subject reaching the image plane I is photoelectrically converted by the imaging element 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 according to the user's operation. In addition, the camera can be a mirrorless camera or a single-lens reflex type camera having a quick return mirror. In addition, Figure 11 The optical system OL shown is a schematic representation of the optical system possessed by the photographing lens 3, and the lens structure of the optical system OL is not limited to this structure.

[0058] Next, the optical system of the first embodiment will be described. As an example of the optical system OL of the first embodiment, the optical system OL (1) shown is configured to have, 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 negative 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 is performed, the second lens group G2 and the third lens group G3 are moved along the optical axis, and the interval between the adjacent lens groups changes. Figure 1

[0059] On the basis of the above structure, the optical system OL of the first embodiment satisfies the following conditional expression (1).

[0060] 0.20 < DG4 / TL < 0.40... (1)

[0061] wherein DG4: the length on the optical axis of the fourth lens group G4

[0062] TL: the total length of the optical system OL in the infinity focus state

[0063] According to the first embodiment, an optical system in which the aberration variation at the time of focusing is small and an optical apparatus provided with the optical system can be obtained. The optical system OL of the first embodiment can also be the optical system OL (2) shown, the optical system OL (3) shown, the optical system OL (4) shown, the optical system OL (5) shown, or the like. Figure 3 Figure 5 Figure 7 Figure 9

[0064]

[0065] ​​​​​​Condition (1) specifies an appropriate relationship between the length of the optical axis of the fourth lens group G4 and the total length of the optical system OL. By satisfying condition (1), the length of the optical axis of the fourth lens group G4 relative to the total length of the optical system OL becomes larger, thus enabling good correction of image plane curvature and coma in the peripheral region throughout the entire magnification range. In addition, in each embodiment, the total length of the optical system OL is the distance along the optical axis from the lens surface closest to the object side of the optical system OL to the image plane I (the distance from the lens surface closest to the image side of the optical system OL to the image plane I is the air conversion distance).

[0066] When the corresponding value of conditional expression (1) deviates from the above range, it becomes difficult to correct for image plane curvature and coma in the peripheral portion of the magnification range. By setting the lower limit of conditional expression (1) to 0.21, 0.23, and further to 0.25, the effects of this embodiment can be obtained more reliably. In addition, by setting the upper limit of conditional expression (1) to 0.38, 0.36, 0.35, and further to 0.33, the effects of this embodiment can be obtained more reliably.

[0067] Next, the optical system of the second embodiment will be described. The optical system of the second embodiment has the same structure as the optical system OL of the first embodiment, and therefore will be described using the same reference numerals as in the first embodiment. For example... Figure 1 As shown, the optical system OL (1), as an example of the optical system OL in the second embodiment, is configured to include a first lens group G1 with positive optical power, a second lens group G2 with negative optical power, a third lens group G3 with positive optical power, and a fourth lens group G4 with negative optical power, arranged sequentially along the optical axis from the object side. During focusing, the second lens group G2 and the third lens group G3 move along the optical axis, and the spacing between adjacent lens groups changes.

[0068] Based on the above structure, the optical system OL of the second embodiment satisfies the following conditional expression (2).

[0069] 3.00<(LnR2+LnR1) / (LnR2-LnR1)<5.00…(2)

[0070] Wherein, LnR1: the radius of curvature of the object-side lens surface in the negative lens located at the image-side of the optical system OL.

[0071] LnR2: The radius of curvature of the image-side lens surface in the negative lens located at the image-side of the optical system OL.

[0072] According to the second embodiment, an optical system with minimal aberration during focusing and an optical device equipped with such an optical system can be obtained. The optical system OL of the second embodiment can also be... Figure 3 The optical system OL(2) shown can also be Figure 5 The optical system OL(3) shown can also be Figure 7 The optical system OL(4) shown can also be Figure 9 The optical system shown

[0073] OL(5).

[0074] Condition (2) specifies an appropriate range for the shape factor of the negative lens located on the image side of the optical system OL. By satisfying condition (2), image plane curvature and coma can be corrected uniformly across the entire magnification range.

[0075] When the corresponding value of condition (2) deviates from the above range, it becomes difficult to uniformly correct for image plane curvature and coma within a portion of the magnification range. By setting the lower limit of condition (2) to 3.05, 3.10, 3.15, 3.20, and further to 3.23, the effects of this embodiment can be obtained more reliably. In addition, by setting the upper limit of condition (2) to 4.90, 4.80, 4.70, 4.60, 4.50, and further to 4.40, the effects of this embodiment can be obtained more reliably.

[0076] Next, the optical system of the third embodiment will be described. The optical system of the third embodiment has the same structure as the optical system OL of the first embodiment, and therefore will be described using the same reference numerals as in the first embodiment. For example... Figure 1 As shown, the optical system OL (1), as an example of the optical system OL in the third embodiment, is configured to include a first lens group G1 with positive optical power, a second lens group G2 with negative optical power, a third lens group G3 with positive optical power, and a fourth lens group G4 with negative optical power, arranged sequentially along the optical axis from the object side. During focusing, the second lens group G2 and the third lens group G3 move along the optical axis, and the spacing between adjacent lens groups changes.

[0077] Based on the above structure, the optical system OL of the third embodiment satisfies the following conditional expression (3).

[0078] 0.75 <f1 / (-f2)<1.30…(3)

[0079] Where f1 is the focal length of the first lens group G1.

[0080] f2: Focal length of the second lens group G2

[0081] According to the third embodiment, an optical system in which the variation in aberration at the time of focusing is small and an optical apparatus provided with the optical system can be obtained. The optical system OL of the third embodiment can also be Figure 3 the optical system OL (2) shown in FIG. 2, can also be Figure 5 the optical system OL (3) shown in FIG. 3, can also be Figure 7 the optical system OL (4) shown in FIG. 4, can also be Figure 9 the optical system shown in FIG. 5

[0082] OL (5).

[0083] Condition formula (3) prescribes the appropriate relationship between the focal length of the first lens group G1 and the focal length of the second lens group G2. By satisfying condition formula (3), the variation in spherical aberration and curvature of field at the time of focusing from an infinite distance object to a close distance object can be suppressed.

[0084] When the corresponding value of condition formula (3) departs from the above range, it is difficult to suppress the variation in spherical aberration and curvature of field at the time of focusing. By setting the lower limit value of condition formula (3) to 0.80, 0.90, 0.95, 1.00, 1.05, and further to 1.10, the effect of the present embodiment can be obtained more reliably. Also, by setting the upper limit value of condition formula (3) to 1.28, 1.25, 1.23, and further to 1.20, the effect of the present embodiment can be obtained more reliably.

[0085] Next, the optical system of the fourth embodiment will be described. The optical system of the fourth embodiment has the same structure as the optical system OL of the first embodiment, and therefore the same symbols as the first embodiment will be attached to describe it. As shown in FIG. 6, the optical system OL (1) as an example of the optical system OL of the fourth embodiment is configured to have, 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 negative refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. At the time of focusing, the second lens group G2 and the third lens group G3 move along the optical axis, and the interval between the adjacent lens groups changes. Figure 1

[0086] On the basis of the above structure, the optical system OL of the fourth embodiment satisfies the following condition formulas (4) to (6).

[0087] 1.80 < ndM1 < 2.20 … (4)

[0088] 26.00 < νdM1 < 28.00 … (5)

[0089] ​θgFM1 < 0.0120... (6)

[0090] ndM1: Abbe number of the negative lens of the first lens group G1

[0091] ndM1: Abbe number of the negative lens of the first lens group G1

[0092] θgFM1: relative partial dispersion of the negative lens of the first lens group G1, defined by the following equation when the refractive index of the negative lens of the first lens group G1 with respect to the g-line is denoted by ngM1, the refractive index of the negative lens of the first lens group G1 with respect to the F-line is denoted by nFM1, and the refractive index of the negative lens of the first lens group G1 with respect to the C-line is denoted by nCM1, that is,

[0093] θgFM1 = (ngM1 - nFM1) / (nFM1 - nCM1)

[0094] According to the fourth embodiment, an optical system in which aberration variation at the time of focusing is small and an optical apparatus provided with the optical system can be obtained. The optical system OL of the fourth embodiment can also be the optical system OL (2) shown in FIG. 2, can also be the optical system OL (3) shown in FIG. 3, can also be the optical system OL (4) shown in FIG. 4, and can also be the optical system OL (5) shown in FIG. 5. Figure 3 The optical system OL (2) shown in FIG. 2, can also be the optical system OL (3) shown in FIG. 3, can also be the optical system OL (4) shown in FIG. 4, and can also be the optical system OL (5) shown in FIG. 5. Figure 5 The optical system OL (2) shown in FIG. 2, can also be the optical system OL (3) shown in FIG. 3, can also be the optical system OL (4) shown in FIG. 4, and can also be the optical system OL (5) shown in FIG. 5. Figure 7 The optical system OL (2) shown in FIG. 2, can also be the optical system OL (3) shown in FIG. 3, can also be the optical system OL (4) shown in FIG. 4, and can also be the optical system OL (5) shown in FIG. 5. Figure 9 The optical system OL (2) shown in FIG. 2, can also be the optical system OL (3) shown in FIG. 3, can also be the optical system OL (4) shown in FIG. 4, and can also be the optical system OL (5) shown in FIG. 5.

[0095] The optical system OL (2) shown in FIG. 2, can also be the optical system OL (3) shown in FIG. 3, can also be the optical system OL (4) shown in FIG. 4, and can also be the optical system OL (5) shown in FIG. 5.

[0096] Condition formula (4) specifies an appropriate range for the refractive index of the negative lens of the first lens group G1 with respect to the d-line. Condition formula (5) specifies an appropriate range for the Abbe number of the negative lens of the first lens group G1. Condition formula (6) specifies an appropriate relationship between the relative partial dispersion and the Abbe number of the negative lens of the first lens group G1. By satisfying condition formulas (4) to (6), axial chromatic aberration and magnification chromatic aberration can be corrected well in the entire region of the magnification range.

[0097] When the corresponding value of condition formula (4) deviates from the above range, it is difficult to correct axial chromatic aberration and magnification chromatic aberration in a part of the magnification range. By setting the lower limit value of condition formula (4) to 1.82, 1.83, and further to 1.84, the effects of the present embodiment can be obtained more reliably.

[0098] When the corresponding value of conditional expression (5) departs from the above range, it is difficult to correct the axial chromatic aberration and the magnification chromatic aberration in a part of the magnification range. By setting the upper limit value of conditional expression (5) to 25.90, 25.85, 25.70, 25.50, and further to 25.35, the effect of the present embodiment can be more reliably obtained.

[0099] When the corresponding value of conditional expression (6) departs from the above range, it is difficult to correct the axial chromatic aberration and the magnification chromatic aberration in a part of the magnification range. By setting the upper limit value of conditional expression (6) to 0.0115, 0.0110, 0.0105, 0.0100, and further to 0.0098, the effect of the present embodiment can be more reliably obtained. In addition, the lower limit of conditional expression (6) can be made larger than 0.0000.

[0100] The optical system OL of the second to fourth embodiments preferably satisfies the above conditional expression (1). By satisfying conditional expression (1), as with the first embodiment, the image surface curvature and the coma in the peripheral portion can be corrected well in the entire region of the magnification range. By setting the lower limit value of conditional expression (1) to 0.21, 0.23, and further to 0.25, the effect of each embodiment can be more reliably obtained. In addition, by setting the upper limit value of conditional expression (1) to 0.38, 0.36, 0.35, and further to 0.33, the effect of each embodiment can be more reliably obtained.

[0101] The optical system OL of the third and fourth embodiments preferably satisfies the above conditional expression (2). By satisfying conditional expression (2), as with the second embodiment, the image surface curvature and the coma can be corrected uniformly in the image surface in the entire region of the magnification range. By setting the lower limit value of conditional expression (2) to 3.05, 3.10, 3.15, 3.20, and further to 3.23, the effect of each embodiment can be more reliably obtained. In addition, by setting the upper limit value of conditional expression (2) to 4.90, 4.80, 4.70, 4.60, 4.50, and further to 4.40, the effect of each embodiment can be more reliably obtained.

[0102] The optical system OL of the fourth embodiment preferably satisfies the above conditional expression (3). By satisfying the conditional expression (3), as with the third embodiment, it is difficult to suppress the variation in spherical aberration and curvature of field at the time of focusing from an infinite distance object to a close distance object. By setting the lower limit value of the conditional expression (3) to 0.80, 0.90, 0.95, 1.00, 1.05, and further to 1.10, the effect of the present embodiment can be obtained more reliably. Further, by setting the upper limit value of the conditional expression (3) to 1.28, 1.25, 1.23, and further to 1.20, the effect of the present embodiment can be obtained more reliably.

[0103] The optical system OL of the first to fourth embodiments preferably satisfies the following conditional expression (7).

[0104] 0.75 < f1 / f3 < 1.20... (7)

[0105] wherein f1: focal length of the first lens group G1

[0106] f3: focal length of the third lens group G3

[0107] The conditional expression (7) specifies an appropriate relationship between the focal length of the first lens group G1 and the focal length of the third lens group G3. By satisfying the conditional expression (7), it is possible to suppress the variation in spherical aberration and curvature of field at the time of focusing from an infinite distance object to a close distance object.

[0108] When the corresponding value of the conditional expression (7) departs from the above range, it is difficult to suppress the variation in spherical aberration and curvature of field at the time of focusing. By setting the lower limit value of the conditional expression (7) to 0.80, 0.85, 0.90, 0.95, and further to 1.00, the effect of each embodiment can be obtained more reliably. Further, by setting the upper limit value of the conditional expression (7) to 1.18, 1.15, 1.13, and further to 1.10, the effect of each embodiment can be obtained more reliably.

[0109] The optical system OL of the first to fourth embodiments preferably satisfies the following conditional expression (8).

[0110] 0.45 < (-β)... (8)

[0111] wherein β: lateral magnification of the optical system OL

[0112] The conditional expression (8) defines an appropriate range for the lateral magnification of the entire system of the optical system OL. By satisfying the conditional expression (8), it is possible to perform photography at the closest focusing distance, and thus is preferable. By setting the lower limit value of the conditional expression (8) to 0.52, 0.55, 0.60, 0.70, 0.75, and further to 0.80, it is possible to more reliably obtain the effects of the embodiments.

[0113] The optical system OL of the first to fourth embodiments preferably satisfies the following conditional expression (9).

[0114] 35.0 < β2 / β3 < 350.0... (9)

[0115] where β2: lateral magnification of the second lens group G2 in the infinity focus state

[0116] β3: lateral magnification of the third lens group G3 in the infinity focus state

[0117] The conditional expression (9) defines an appropriate relationship between the lateral magnification of the second lens group G2 in the infinity focus state and the lateral magnification of the third lens group G3 in the infinity focus state. By satisfying the conditional expression (9), it is possible to suppress the variation in the curvature of field and the spherical aberration at the time of focusing.

[0118] When the corresponding value of the conditional expression (9) departs from the above range, it is difficult to suppress the variation in the curvature of field and the spherical aberration at the time of focusing. By setting the lower limit value of the conditional expression (9) to 35.50, 36.00, 36.50, 37.00, and further to 37.30, it is possible to more reliably obtain the effects of the embodiments. In addition, by setting the upper limit value of the conditional expression (9) to 300.00, 250.00, 200.00, 150.00, 100.00, 85.00, and further to 75.00, it is possible to more reliably obtain the effects of the embodiments.

[0119] The optical system OL of the first to fourth embodiments can also satisfy the following conditional expression (10).

[0120] 0.005 < β3 / β2 < 0.035... (10)

[0121] where β2: lateral magnification of the second lens group G2 in the infinity focus state

[0122] β3: lateral magnification of the third lens group G3 in the infinity focus state

[0123] Condition formula (10) prescribes an appropriate relationship between the lateral magnification of the second lens group G2 and the lateral magnification of the third lens group G3 in the infinity focus state. By satisfying condition formula (10), it is possible to suppress the variation in the curvature of field and the spherical aberration at the time of focusing.

[0124] When the corresponding value of condition formula (10) departs from the above range, it is difficult to suppress the variation in the curvature of field and the spherical aberration at the time of focusing. By setting the lower limit value of condition formula (10) to 0.008, 0.010, and further to 0.012, it is possible to more reliably obtain the effects of the embodiments. Also, by setting the upper limit value of condition formula (10) to 0.033, 0.030, and further to 0.029, it is possible to more reliably obtain the effects of the embodiments.

[0125] The optical system OL of the first to fourth embodiments preferably satisfies the following condition formula (11).

[0126] {β2 + (1 / β2)} -2 <0.10... (11)

[0127] where β2: lateral magnification of the second lens group G2 in the infinity focus state

[0128] Condition formula (11) prescribes an appropriate range for the lateral magnification of the second lens group G2 in the infinity focus state. By satisfying condition formula (11), it is possible to well correct each aberration such as the spherical aberration or the curvature of field in the infinity focus state.

[0129] When the corresponding value of condition formula (11) departs from the above range, it is difficult to correct each aberration such as the spherical aberration or the curvature of field in the infinity focus state. By setting the upper limit value of condition formula (11) to 0.08, 0.06, and further to 0.05, it is possible to more reliably obtain the effects of the embodiments.

[0130] The optical system OL of the first to fourth embodiments preferably satisfies the following condition formula (12).

[0131] {β3 + (1 / β3)} -2 <0.10... (12)

[0132] where β3: lateral magnification of the third lens group G3 in the infinity focus state

[0133] Condition formula (12) prescribes an appropriate range for the lateral magnification of the third lens group G3 in the infinity focus state. By satisfying condition formula (12), it is possible to well correct each aberration such as the spherical aberration or the curvature of field in the infinity focus state.

[0134] When the corresponding value of conditional expression (12) departs from the above range, it is difficult to correct each aberration such as spherical aberration or image surface curvature in an infinite focus state. By setting the upper limit value of conditional expression (12) to 0.08, 0.06, and further to 0.05, the effect of each embodiment can be more reliably obtained.

[0135] The optical system OL of the first to fourth embodiments preferably satisfies the following conditional expression (13).

[0136] 0.05 < Bf / TL < 0.35... (13)

[0137] where Bf: back focal distance of the optical system OL in an infinite focus state

[0138] TL: total length of the optical system OL in an infinite focus state

[0139] Conditional expression (13) specifies an appropriate relationship between the back focal distance of the optical system OL and the total length of the optical system OL. In each embodiment, the back focal distance of the optical system OL is the distance (air conversion distance) on the optical axis from the most image side lens surface of the optical system OL to the image surface I. By satisfying conditional expression (13), it is possible to well suppress the generation of each aberration, and an optical system with a short back focal distance can be obtained. By setting the lower limit value of conditional expression (13) to 0.06, 0.07, and further to 0.08, the effect of each embodiment can be more reliably obtained. Further, by setting the upper limit value of conditional expression (13) to 0.33, 0.30, 0.25, 0.20, 0.18, and further to 0.15, the effect of each embodiment can be more reliably obtained.

[0140] The optical system OL of the first to fourth embodiments preferably satisfies the following conditional expression (14).

[0141] 0.10 < Bf / f < 0.50... (14)

[0142] where Bf: back focal distance of the optical system OL in an infinite focus state

[0143] f: focal distance of the optical system OL

[0144] The conditional expression (14) specifies an appropriate relationship of the back focal length of the optical system OL to the focal length of the optical system OL. By satisfying the conditional expression (14), it is possible to well suppress generation of each aberration, and it is possible to obtain an optical system with a short back focal length. By setting the lower limit value of the conditional expression (14) to 0.12, 0.14, further to 0.15, it is possible to more reliably obtain the effects of each embodiment. In addition, by setting the upper limit value of the conditional expression (20) to 0.45, 0.40, 0.35, 0.30, 0.25, further to 0.20, it is possible to more reliably obtain the effects of each embodiment.

[0145] It is preferable that the optical system OL of the first to fourth embodiments has an aperture (aperture stop) S, and satisfies the following conditional expression (15).

[0146] 0.50 < L1S / SLn < 1.00... (15)

[0147] wherein L1S: a distance on the optical axis from the most object side lens surface of the optical system OL to the aperture S in the infinity focus state

[0148] SLn: a distance on the optical axis from the aperture S to the most image side lens surface of the optical system OL in the infinity focus state

[0149] The conditional expression (15) specifies an appropriate relationship of the distance on the optical axis from the most object side lens surface of the optical system OL to the aperture S to the distance on the optical axis from the aperture S to the most image side lens surface of the optical system OL. By satisfying the conditional expression (15), it is possible to obtain an optical system in which generation of each aberration in the peripheral portion is well suppressed. By setting the lower limit value of the conditional expression (15) to 0.52, 0.55, 0.58, further to 0.60, it is possible to more reliably obtain the effects of each embodiment. In addition, by setting the upper limit value of the conditional expression (15) to 0.95, 0.90, 0.88, 0.85, 0.83, further to 0.80, it is possible to more reliably obtain the effects of each embodiment. In addition, the aperture (aperture stop) S is preferably disposed between the second lens group G2 and the third lens group G3.

[0150] The optical system OL of the first to fourth embodiments preferably satisfies the following conditional expression (16).

[0151] 0.70 < Mf2 / Mf3 < 1.10... (16)

[0152] wherein Mf2: an absolute value of the moving amount of the second lens group G2 when focusing from an infinity object to a closest focus distance object

[0153] Mf3: absolute value of moving amount of the third lens group G3 when focusing from an object at infinity to an object at the closest focusing distance

[0154] Condition expression (16) defines an appropriate relationship between the moving amount of the second lens group G2 and the moving amount of the third lens group G3 when focusing. In addition, the closest focusing distance corresponds to the shortest photographing distance. By satisfying condition expression (16), it is possible to suppress variations in spherical aberration and curvature of field when focusing from an object at infinity to an object at a close distance.

[0155] When the corresponding value of condition expression (16) departs from the above range, it is difficult to suppress variations in spherical aberration and curvature of field when focusing. By setting the lower limit value of condition expression (16) to 0.73, 0.75, 0.78, 0.80, and further to 0.82, it is possible to more reliably obtain the effects of the embodiments. In addition, by setting the upper limit value of condition expression (16) to 0.99, 0.98, and further to 0.97, it is possible to more reliably obtain the effects of the embodiments.

[0156] In the optical system OL of the first to fourth embodiments, it is preferable that the third lens group G3 have a negative lens satisfying the following condition expressions (17) to (19).

[0157] 1.80 < ndM3 < 2.00 … (17)

[0158] 26.00 < νdM3 < 30.00 … (18)

[0159] θgFM3 < 0.0120 … (19)

[0160] where ndM3: refractive index with respect to d-line of the negative lens of the third lens group G3

[0161] νdM3: Abbe number of the negative lens of the third lens group G3

[0162] θgFM3: relative partial dispersion of the negative lens of the third lens group G3, defined by the following expression when the refractive index with respect to g-line of the negative lens of the third lens group G3 is ngM3, the refractive index with respect to F-line of the negative lens of the third lens group G3 is nFM3, and the refractive index with respect to C-line of the negative lens of the third lens group G3 is nCM3, that is,

[0163] θgFM3 = (ngM3 - nFM3) / (nFM3 - nCM3)

[0164] The conditional expression (17) specifies an appropriate range for the refractive index with respect to the d-line of the negative lens of the third lens group G3. The conditional expression (18) specifies an appropriate range for the Abbe number of the negative lens of the third lens group G3. The conditional expression (19) specifies an appropriate relationship between the relative partial dispersion and the Abbe number of the negative lens of the third lens group G3. By satisfying the conditional expressions (17) to (19), it is possible to suppress the variation in the axial chromatic aberration when focusing from an infinite distance object to a close distance object.

[0165] When the corresponding value of the conditional expression (17) departs from the above range, it is difficult to suppress the variation in the axial chromatic aberration when focusing. By setting the lower limit value of the conditional expression (17) to 1.82, 1.83, and further to 1.84, it is possible to more reliably obtain the effects of the respective embodiments.

[0166] When the corresponding value of the conditional expression (18) departs from the above range, it is difficult to suppress the variation in the axial chromatic aberration when focusing. By setting the upper limit value of the conditional expression (18) to 25.90, 25.85, 25.70, 25.50, and further to 25.35, it is possible to more reliably obtain the effects of the respective embodiments.

[0167] When the corresponding value of the conditional expression (19) departs from the above range, it is difficult to suppress the variation in the axial chromatic aberration when focusing. By setting the upper limit value of the conditional expression (19) to 0.0115, 0.0110, 0.0105, 0.0100, and further to 0.0098, it is possible to more reliably obtain the effects of the respective embodiments. In addition, it is also possible to make the lower limit of the conditional expression (19) larger than 0.0000.

[0168] The optical system OL of the first to fourth embodiments preferably satisfies the following conditional expression (20).

[0169] (L1R2+L1R1) / (L1R2-L1R1) < 0.10... (20)

[0170] where L1R1: radius of curvature of an object side lens surface of a positive lens disposed at the most object side of the optical system OL

[0171] L1R2: radius of curvature of an image side lens surface of a positive lens disposed at the most object side of the optical system OL

[0172] The conditional expression (20) specifies an appropriate range for the shape factor of the positive lens disposed at the most object side of the optical system OL. By satisfying the conditional expression (20), it is possible to well correct the spherical aberration in the infinite focus state.

[0173] When the corresponding value of conditional expression (20) departs from the above range, it is difficult to correct the spherical aberration in the state of focusing at infinity. By setting the upper limit value of conditional expression (20) to 0.00, -0.01, -0.03, -0.08, -0.10, -0.30, -0.50, and further to -0.60, the effect of each embodiment can be more reliably obtained. In addition, the lower limit value of conditional expression (20) can be set to -2.00, -1.80, -1.50, -1.45, and further to -1.40.

[0174] In the optical system OL of the first to fourth embodiments, it is preferable that the lens disposed at the most image side of the fourth lens group G4 has a negative refractive power. Thereby, the image surface curvature and coma in the peripheral portion can be well corrected in the entire region of the magnification range.

[0175] In the optical system OL of the first to fourth embodiments, it is preferable that, when focusing from an object at infinity to an object at close range, the second lens group G2 moves toward the image side along the optical axis, and the third lens group G3 moves toward the object side along the optical axis. In the optical system OL of the first to fourth embodiments, it is preferable that, when focusing, the position of the first lens group G1 relative to the image plane I is fixed. In the optical system OL of the first to fourth embodiments, it is preferable that, when focusing, the position of the fourth lens group G4 relative to the image plane I is fixed. Thereby, the variation in aberration when focusing can be suppressed.

[0176] In addition, in the optical system OL of the first to fourth embodiments, it is preferable that at least one lens surface of the negative lens disposed at the most image side of the optical system OL is an aspherical surface. Thereby, the image surface curvature can be uniformly corrected in the image plane.

[0177] Next, the manufacturing method of the optical system OL of the first embodiment will be described with reference to Figure 12 First, the first lens group G1 having a positive refractive power, the second lens group G2 having a negative refractive power, the third lens group G3 having a positive refractive power, and the fourth lens group G4 having a negative refractive power are sequentially disposed from the object side along the optical axis (step ST1). Next, the manufacturing method is configured such that, when focusing, the second lens group G2 and the third lens group G3 move along the optical axis, and the interval between the adjacent lens groups changes (step ST2). Further, the lenses are disposed in the lens barrel so as to at least satisfy the above conditional expression (1) (step ST3). According to this manufacturing method, an optical system having less variation in aberration when focusing can be manufactured.

[0178] Next, the manufacturing method of the optical system OL of the second embodiment will be outlined. The manufacturing method of the optical system OL of the second embodiment is the same as the manufacturing method described in the first embodiment, and thus the same reference will be made to the first embodiment Figure 12 will be described. First, the first lens group Gl having a positive refractive power, the second lens group G2 having a negative refractive power, the third lens group G3 having a positive refractive power, and the fourth lens group G4 having a negative refractive power are sequentially arranged along the optical axis from the object side (step ST1). Next, the manufacturing method is configured such that, at the time of focusing, the second lens group G2 and the third lens group G3 move along the optical axis, and the intervals between the adjacent lens groups change (step ST2). Also, the lenses are arranged in the lens barrel so as to at least satisfy the above conditional expression (2) (step ST3). According to this manufacturing method, an optical system having less variation in aberration at the time of focusing can be manufactured.

[0179] Next, the manufacturing method of the optical system OL of the third embodiment will be outlined. The manufacturing method of the optical system OL of the third embodiment is the same as the manufacturing method described in the first embodiment, and thus the same reference will be made to the first embodiment Figure 12 will be described. First, the first lens group Gl having a positive refractive power, the second lens group G2 having a negative refractive power, the third lens group G3 having a positive refractive power, and the fourth lens group G4 having a negative refractive power are sequentially arranged along the optical axis from the object side (step ST1). Next, the manufacturing method is configured such that, at the time of focusing, the second lens group G2 and the third lens group G3 move along the optical axis, and the intervals between the adjacent lens groups change (step ST2). Also, the lenses are arranged in the lens barrel so as to at least satisfy the above conditional expression (3) (step ST3). According to this manufacturing method, an optical system having less variation in aberration at the time of focusing can be manufactured.

[0180] Next, the manufacturing method of the optical system OL of the fourth embodiment will be outlined with reference to Figure 13 , the first lens group Gl having a positive refractive power, the second lens group G2 having a negative refractive power, the third lens group G3 having a positive refractive power, and the fourth lens group G4 having a negative refractive power are sequentially arranged along the optical axis from the object side (step ST11). Next, the manufacturing method is configured such that, at the time of focusing, the second lens group G2 and the third lens group G3 move along the optical axis, and the intervals between the adjacent lens groups change (step ST12). Also, the lenses are arranged in the lens barrel so as to at least the first lens group Gl has a negative lens satisfying the above conditional expressions (4) to (6) (step ST13). According to this manufacturing method, an optical system having less variation in aberration at the time of focusing can be manufactured.

[0181] Example

[0182] Hereinafter, the optical system OL of each embodiment will be described with reference to the drawings. Figure 1 Figure 3 Figure 5 Figure 7 Figure 9 are sectional views showing the structures and power distributions of the optical systems OL {OL(1) to OL(5)} of the first to fifth embodiments. In the sectional views of the optical systems OL(1) to OL(5) of the first to fifth embodiments, the moving directions of each lens group along the optical axis at the time of focusing from an infinite distance to a close object (finite distance object) are shown with arrows together with the word "focus".

[0183] In these Figure 1 Figure 3 Figure 5 Figure 7 Figure 9 In these tables, each lens group is represented by a combination of a symbol G and a number, and each lens is represented by a combination of a symbol L and a number. At this time, in order to prevent the types and the number of digits of the symbols and the numbers from becoming complicated, the combination of the symbol and the number is used to represent the lens group and the like independently for each embodiment. Therefore, even if the same combination of the symbol and the number is used between the embodiments, it does not mean the same structure.

[0184] Tables 1 to 5 are shown below. Table 1 is a table showing each parameter data in the first embodiment, Table 2 is a table showing each parameter data in the second embodiment, Table 3 is a table showing each parameter data in the third embodiment, Table 4 is a table showing each parameter data in the fourth embodiment, and Table 5 is a table showing each parameter data in the fifth embodiment. In each embodiment, as the calculation targets of the aberration characteristics, the d line (wavelength λ = 587.6 nm), the g line (wavelength λ = 435.8 nm), the C line (wavelength λ = 656.3 nm), and the F line (wavelength λ = 486.1 nm) are selected.

[0185] In the table of [overall parameters], f represents the focal length of the entire optical system, 2ω represents the field angle (unit: ° (degree), and ω is the half field angle), and Ymax represents the maximum image height. TL represents a distance obtained by adding Bf to the distance on the optical axis from the frontmost surface of the lens to the final surface of the lens in the infinite focus state, and Bf represents the air conversion distance (back focal length) from the final surface of the lens to the image plane in the infinite focus state. In addition, in the table of [overall parameters], β2 represents the lateral magnification of the second lens group in the infinite focus state. β3 represents the lateral magnification of the third lens group in the infinite focus state. Mf2 represents the absolute value of the movement amount of the second lens group at the time of focusing from an infinite distance object to a closest focus distance object. Mf3 represents the absolute value of the movement amount of the third lens group at the time of focusing from an infinite distance object to a closest focus distance object.​​​​​​​​

[0186] In the table of [lens parameters], the surface number indicates the order of the optical surface from the object side along the direction of the ray traveling, R indicates the radius of curvature of each optical surface (a value positive for a surface with the center of curvature on the image side), D indicates the distance on the optical axis from each optical surface to the next optical surface (or the image surface), that is, the surface interval, nd indicates the refractive index for the d-line of the material of the optical member, vd indicates the Abbe number of the material of the optical member with the d-line as the reference, and θgF indicates the relative partial dispersion of the material of the optical member. "∞" for the radius of curvature indicates a plane or an opening, and (aperture S) indicates the aperture stop S. The refractive index nd = 1.00000 of air is omitted. When the optical surface is an aspherical surface, an asterisk is attached to the surface number, and the paraxial radius of curvature R is shown in the column of the radius of curvature.

[0187] The refractive index for the g-line (wavelength λ = 435.8 nm) of the material of the optical member is made ng, the refractive index for the F-line (wavelength λ = 486.1 nm) of the material of the optical member is made nF, and the refractive index for the C-line (wavelength λ = 656.3 nm) of the material of the optical member is made nC. At this time, the relative partial dispersion θgF of the material of the optical member is defined by the following formula (A).

[0188] θgF = (ng - nF) / (nF - nC)... (A)

[0189] In the table of [aspherical surface data], the aspherical surface indicated in [lens parameters] is shown by the following formula (B). X(y) indicates the distance (amount of sag) in the direction of 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 indicates the radius of curvature of the reference sphere (paraxial radius of curvature), K indicates the conic constant, and Ai indicates the i-th aspherical coefficient. "E-n" indicates "x 10 -n ". For example, 1.234E-05 = 1.234 x 10 -5 . In addition, the second aspherical coefficient A2 is 0, and the description thereof is omitted.

[0190] X(y) = (y 2 / R) / {1 + (1 - κ x y 2 / R 2 ) 1 / 2} + A4 x y 4 + A6 x y 6 + A8 x y 8 + A10 x y 10 + A12 x y 12 ... (B)

[0191] In the table of [Variable interval data], the surface interval at the surface number i where the surface interval becomes (Di) in the table of [Lens parameter] is shown. In addition, DO indicates the distance from the object to the most object side optical surface in the optical system. In the table of [Variable interval data], f indicates the focal length of the entire system of the optical system, β indicates the photographing magnification (lateral magnification) of the optical system, and FN0 indicates the F value of the optical system.

[0192] In the table of [Lens group data], the initial surface (the most object side surface) and the focal length of each lens group are shown.

[0193] Hereinafter, among all the parameter values, "mm" is generally used for the disclosed focal length f, the radius of curvature R, the surface interval D, other lengths, and the like, in the case where it is not particularly described, but the same optical performance can be obtained even if the optical system is scaled up or scaled down, and thus it is not limited thereto.

[0194] The explanation of the tables up to this point is the same in all the embodiments, and the repeated explanation is omitted hereinafter.

[0195] (First Embodiment)

[0196] Use Figures 1-2 The first embodiment is explained using Table 1. Figure 1 is a diagram showing the lens structure of the optical system of the first embodiment. The optical system OL(1) of the first embodiment is composed of the first lens group G1 having a positive refractive power, the second lens group G2 having a negative refractive power, the third lens group G3 having a positive refractive power, and the fourth lens group G4 having a negative refractive power, which are arranged in order from the object side along the optical axis. When focusing from an infinite distance object to a close distance object, the second lens group G2 moves toward the image side along the optical axis, the third lens group G3 moves toward the object side along the optical axis, and the interval between the adjacent lens groups changes. In addition, when focusing, the positions of the first lens group G1 and the fourth lens group G4 relative to the image plane I are fixed. The aperture stop S is disposed between the second lens group G2 and the third lens group G3. When focusing, the position of the aperture stop S relative to the image plane I is fixed. The symbol (+) or (-) attached to the symbol of each lens group indicates the refractive power of each lens group, which is the same in all the embodiments hereinafter.

[0197] The first lens group G1 is composed of a biconvex positive lens L11, a negative meniscus lens L12 having a convex surface toward the object side, a positive meniscus lens L13 having a convex surface toward the object side, and a positive meniscus lens L14 having a convex surface toward the object side, which are arranged in order from the object side along the optical axis. In the present embodiment, the negative meniscus lens L12 of the first lens group G1 corresponds to a negative lens satisfying the conditional expressions (4) to (6).

[0198] The second lens group G2 is composed of a biconcave negative lens L21 arranged in order from the object side along the optical axis, and a joint lens composed of a negative meniscus lens L22 having a convex surface toward the object side and a positive meniscus lens L23 having a convex surface toward the object side.

[0199] The third lens group G3 is composed of a biconvex positive lens L31 arranged in order from the object side along the optical axis, and a joint lens composed of a negative meniscus lens L32 having a convex surface toward the object side and a biconvex positive lens L33. In the present embodiment, the negative meniscus lens L32 of the third lens group G3 corresponds to a negative lens satisfying the conditional expressions (17) to (19).

[0200] The fourth lens group G4 is composed of a negative meniscus lens L41 having a convex surface toward the object side, a joint lens composed of a negative meniscus lens L42 having a convex surface toward the object side and a positive meniscus lens L43 having a convex surface toward the object side, a joint lens composed of a negative meniscus lens L44 having a convex surface toward the object side and a positive meniscus lens L45 having a convex surface toward the object side, and a negative meniscus lens L46 having a concave surface toward the object side. The object side lens surface of the negative meniscus lens L46 is an aspherical surface. An image surface I is disposed on the image side of the fourth lens group G4.

[0201] In Table 1 below, values of parameters of the optical system of the first embodiment are shown.

[0202] (Table 1)

[0203] [Overall Parameters]

[0204]

[0205]

[0206] [Overall Parameters]

[0207]

[0208]

[0209] [Overall Parameters]

[0210] 27th Surface

[0211] K = 1.000, A4 = 9.61768E-06, A6 = 1.56877E-08

[0212] A8 = -4.92862E-11, A10 = -1.29299E-13, A12 = -7.46540E-17

[0213] [Variable Separation Data]

[0214]

[0215] [Data of lens group]

[0216]

[0217] Figure 2 (A) of FIG. 1 is a graph showing each aberration of the optical system of the first embodiment in an infinite focus state. Figure 2 (B) of FIG. 1 is a graph showing each aberration of the optical system of the first embodiment in a closest focus distance focus state (photographic magnification β = -1.0). In each aberration graph in the infinite focus state, FNO indicates the F value, and Y indicates the image height. In each aberration graph in the closest focus distance focus state, NA indicates the numerical aperture, and Y indicates the image height. In addition, in the spherical aberration graph, the value of the F value or the numerical aperture corresponding to the maximum aperture is shown, in the astigmatism graph and the distortion graph, the maximum value of the image height is shown, respectively, and in the coma graph, the value of each image height is shown. d indicates the d line (wavelength λ = 587.6 nm), g indicates the g line (wavelength λ = 435.8 nm), C indicates the C line (wavelength λ = 656.3 nm), and F indicates the F line (wavelength λ = 486.1 nm). In the astigmatism graph, the solid line indicates the sagittal image surface, and the broken line indicates the tangential image surface. In addition, in the aberration graphs of each of the embodiments shown below, the same symbols as in the present embodiment are used, and the repeated explanation is omitted.

[0218] As is apparent from each aberration graph, the optical system of the first embodiment has excellent imaging performance because each aberration is well corrected in the entire region from the infinite focus state to the closest focus distance focus state.

[0219] (Second Embodiment)

[0220] The second embodiment will be described using Table 2. Figures 3-4 Figure 3 is a graph showing the lens structure of the optical system of the second embodiment. The optical system OL(2) of the second embodiment is composed of the first lens group G1 having a positive refractive power, the second lens group G2 having a negative refractive power, the third lens group G3 having a positive refractive power, and the fourth lens group G4 having a negative refractive power, which are arranged in order from the object side along the optical axis. When focusing from an infinite object to a close object, the second lens group G2 moves toward the image side along the optical axis, the third lens group G3 moves toward the object side along the optical axis, and the interval between the adjacent lens groups changes. In addition, when focusing, the positions of the first lens group G1 and the fourth lens group G4 relative to the image plane I are fixed. The aperture stop S is disposed between the second lens group G2 and the third lens group G3. When focusing, the position of the aperture stop S relative to the image plane I is fixed.

[0221] ​In the second embodiment, the second lens group G2, the third lens group G3, and the fourth lens group G4 are configured in the same way as in the first embodiment, and therefore are given the same reference numerals as in the first embodiment, and detailed descriptions of these lenses are omitted. The first lens group G1 is composed of a positive meniscus lens L11 with its concave surface facing the object side, arranged sequentially along the optical axis from the object side; a combined lens formed by joining a negative meniscus lens L12 with its convex surface facing the object side and a positive meniscus lens L13 with its convex surface facing the object side; and a positive meniscus lens L14 with its convex surface facing the object side. In this embodiment, the negative meniscus lens L12 of the first lens group G1 is equivalent to a negative lens that satisfies conditions (4) to (6). In addition, the negative meniscus lens L32 of the third lens group G3 is equivalent to a negative lens that satisfies conditions (17) to (19).

[0222] Table 2 below shows the values ​​of the parameters of the optical system of the second embodiment.

[0223] (Table 2)

[0224] [Overall Parameters]

[0225]

[0226] [Lens Parameters]

[0227]

[0228]

[0229] [Aspherical Data]

[0230] Page 27, κ = 1.000, A4 = 1.19399E-05, A6 = 2.04728E-08

[0231] A8 = -7.55581E-11, A10 = 2.43965E-13, A12 = -1.86360E-16 [Variable interval data]

[0232]

[0233]

[0234] [Lens Group Data]

[0235]

[0236] Figure 4 (A) is a diagram of aberrations in the infinity focusing state of the optical system of the second embodiment. Figure 4The B) is each aberration diagram in the closest focusing distance focusing state (photographic magnification β = -1.0) of the optical system of the 2nd embodiment. From each aberration diagram, it is understood that the optical system of the 2nd embodiment corrects each aberration well in the entire region from the infinity focusing state to the closest focusing distance focusing state, and has excellent imaging performance.

[0237] (3rd Embodiment)

[0238] The 3rd embodiment will be described using FIG. 15 and Table 3. Figures 5-6 The 3rd embodiment will be described using FIG. 15 and Table 3. Figure 5 is a view showing the lens structure of the optical system of the 3rd embodiment. The optical system OL(3) of the 3rd embodiment is composed of the 1st lens group G1 having a positive refractive power, the 2nd lens group G2 having a negative refractive power, the 3rd lens group G3 having a positive refractive power, and the 4th lens group G4 having a negative refractive power, which are arranged in order from the object side along the optical axis. When focusing from an infinite distance object to a close distance object, the 2nd lens group G2 moves toward the image side along the optical axis, the 3rd lens group G3 moves toward the object side along the optical axis, and the interval between the adjacent lens groups changes. In addition, the 1st lens group G1 and the 4th lens group G4 are fixed in position relative to the image plane I when focusing. The aperture stop S is disposed between the 2nd lens group G2 and the 3rd lens group G3. The aperture stop S is fixed in position relative to the image plane I when focusing.

[0239] In the 3rd embodiment, the 2nd lens group G2, the 3rd lens group G3, and the 4th lens group G4 are configured similarly to the 1st embodiment, and therefore the same symbols as in the case of the 1st embodiment are attached, and detailed description of these lenses will be omitted. The 1st lens group G1 is composed of a biconvex positive lens L11, a cemented lens in which a negative meniscus lens L12 having a convex surface toward the object side and a positive meniscus lens L13 having a convex surface toward the object side are cemented, and a positive meniscus lens L14 having a convex surface toward the object side, which are arranged in order from the object side along the optical axis. The object side lens surface of the positive meniscus lens L14 is an aspherical surface. In the present embodiment, the negative meniscus lens L12 of the 1st lens group G1 corresponds to a negative lens satisfying the conditional expressions (4) to (6). In addition, the negative meniscus lens L32 of the 3rd lens group G3 corresponds to a negative lens satisfying the conditional expressions (17) to (19).

[0240] In Table 3 below, the values of the parameters of the optical system of the 3rd embodiment are shown.

[0241] (Table 3)

[0242] [Overall Parameters]

[0243]

[0244] [Lens Parameters]

[0245]

[0246]

[0247] [Aspherical surface data]

[0248] Surface No. 6 k = 1.000, A4 = -7.80076E-08, A6 = 7.83037E-11

[0249] A8 = -1.44363E-13, A10 = 0.00000E+00, A12 = 0.00000E+00 Surface No. 27 k = 1.000, A4 = 1.27301E-05, A6 = 1.49611E-08

[0250] A8 = 9.59928E-12, A10 = -4.03456E-15, A12 = 3.26570E-16

[0251] [Variable interval data]

[0252]

[0253] [Lens group data]

[0254]

[0255] Figure 6 (A) is a graph of each aberration of the optical system of the 3rd embodiment in an infinite focus state. Figure 6 (B) is a graph of each aberration of the optical system of the 3rd embodiment in a closest focus distance focus state (photographic magnification β = -1.0). As is apparent from the graphs of each aberration, the optical system of the 3rd embodiment corrects each aberration well in the entire region from the infinite focus state to the closest focus distance focus state, and has excellent imaging performance.

[0256] (4th Embodiment)

[0257] Using Figures 7-8 The 4th embodiment is explained with reference to Table 4. Figure 7Fig. 4 is a view showing a lens structure of the optical system of the 4th embodiment. The optical system OL(4) of the 4th embodiment is composed of a 1st lens group G1 having a positive refractive power, a 2nd lens group G2 having a negative refractive power, a 3rd lens group G3 having a positive refractive power, and a 4th lens group G4 having a negative refractive power, which are arranged in this order from the object side along the optical axis. When focusing from an infinite distance object to a close distance object, the 2nd lens group G2 is moved toward the image side along the optical axis, the 3rd lens group G3 is moved toward the object side along the optical axis, and the interval between the adjacent lens groups is changed. In addition, the 1st lens group G1 and the 4th lens group G4 are fixed in position relative to the image plane I when focusing. The aperture stop S is disposed between the 2nd lens group G2 and the 3rd lens group G3. The aperture stop S is fixed in position relative to the image plane I when focusing.

[0258] In the 4th embodiment, the 2nd lens group G2 and the 3rd lens group G3 are constructed similarly to the 1st embodiment, so the same symbols as in the case of the 1st embodiment are attached, and detailed description of these lenses will be omitted. The 1st lens group G1 is composed of a biconvex positive lens L11, a negative meniscus lens L12 having a convex surface toward the object side, a cemented lens composed of a biconvex positive lens L13 and a positive meniscus lens L14 having a convex surface toward the object side, which are arranged in this order from the object side along the optical axis. The object side lens surface of the positive meniscus lens L14 is aspherical. In this embodiment, the negative meniscus lens L12 of the 1st lens group G1 corresponds to a negative lens satisfying the conditional expressions (4) to (6). In addition, the negative meniscus lens L32 of the 3rd lens group G3 corresponds to a negative lens satisfying the conditional expressions (17) to (19).

[0259] The 4th lens group G4 is composed of a biconcave negative lens L41, a negative meniscus lens L42 having a convex surface toward the object side, a cemented lens composed of the negative meniscus lens L42 and a positive meniscus lens L43 having a convex surface toward the object side, a cemented lens composed of a negative meniscus lens L44 having a convex surface toward the object side and a biconvex positive lens L45, and a negative meniscus lens L46 having a concave surface toward the object side, which are arranged in this order from the object side along the optical axis. The object side lens surface of the negative meniscus lens L46 is aspherical. The image plane I is disposed on the image side of the 4th lens group G4.

[0260] In Table 4 below, the values of the parameters of the optical system of the 4th embodiment are shown.

[0261] (Table 4)

[0262] [Overall parameters]

[0263]

[0264]

[0265] [Overall parameters]

[0266]

[0267]

[0268] [Aspherical surface data]

[0269] Surface No. 6 κ = 1.000, A4 = -1.39939E-07, A6 = -9.81797E-11

[0270] A8 = -3.74424E-13, A10 = 1.22198E-15, A12 = -1.93260E-18 Surface No. 27 κ = 1.000, A4 = 1.58902E-05, A6 = 1.67973E-08

[0271] A8 = 2.63185E-11, A10 = -9.61351E-14, A12 = 5.69420E-16 [Variable interval data]

[0272]

[0273] [Aspherical surface data]

[0274]

[0275] Figure 8 (A) is a graph of each aberration of the optical system of the 4th embodiment in an infinite focus state. Figure 8 (B) is a graph of each aberration of the optical system of the 4th embodiment in a closest focus distance focus state (photographic magnification β = -1.0). As is apparent from the graphs of each aberration, the optical system of the 4th embodiment corrects each aberration well in the entire region from the infinite focus state to the closest focus distance focus state, and has excellent imaging performance.

[0276] (5th Embodiment)

[0277] Using Figures 9-10 The 5th embodiment is explained using Table 5. Figure 9Fig. 5 is a diagram showing a lens structure of an optical system according to the fifth embodiment. The optical system OL(5) of the fifth embodiment is composed of a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power, which are arranged in this order from the object side along the optical axis. When focusing from an infinite distance object to a close distance object, the second lens group G2 is moved toward the image side along the optical axis, the third lens group G3 is moved toward the object side along the optical axis, and the interval between the adjacent lens groups changes. In addition, the first lens group G1 and the fourth lens group G4 are fixed in position relative to the image plane I when focusing. The aperture stop S is disposed between the second lens group G2 and the third lens group G3. The aperture stop S is fixed in position relative to the image plane I when focusing.

[0278] In the fifth embodiment, the second lens group G2 and the third lens group G3 are configured as in the first embodiment, and therefore the same reference numerals are attached to the same components as in the case of the first embodiment, and detailed description of these lenses will be omitted. The first lens group G1 is composed of a biconvex positive lens L11, a negative meniscus lens L12 having a convex surface toward the object side, a cemented lens composed of a biconvex positive lens L13 and a positive meniscus lens L14 having a convex surface toward the object side, which are arranged in this order from the object side along the optical axis. In the present embodiment, the negative meniscus lens L12 of the first lens group G1 corresponds to a negative lens satisfying the conditional expressions (4) to (6). In addition, the negative meniscus lens L32 of the third lens group G3 corresponds to a negative lens satisfying the conditional expressions (17) to (19).

[0279] The fourth lens group G4 is composed of a negative meniscus lens L41 having a convex surface toward the object side, a cemented lens composed of a negative meniscus lens L42 having a convex surface toward the object side and a positive meniscus lens L43 having a convex surface toward the object side, a positive meniscus lens L44 having a convex surface toward the object side, a cemented lens composed of a negative meniscus lens L45 having a convex surface toward the object side and a biconvex positive lens L46, and a negative meniscus lens L47 having a concave surface toward the object side, which are arranged in this order from the object side along the optical axis. The object side lens surface of the negative meniscus lens L47 is aspherical. The image plane I is disposed on the image side of the fourth lens group G4.

[0280] In Table 5 below, the values of the parameters of the optical system of the fifth embodiment are shown.

[0281] (Table 5)

[0282] [Overall Parameters]

[0283]

[0284] [Overall Parameters]

[0285]

[0286]

[0287] [Aspherical surface data]

[0288] κ = 1.000, A4 = 1.95940E-05, A6 = -1.65107E-08

[0289] A8 = 2.48794E-10, A10 = -8.47293E-13, A12 = 1.57410E-15 [Variable interval data]

[0290]

[0291]

[0292] [Group data]

[0293]

[0294] Figure 10 (A) of FIG. 5 is a graph of each aberration in an infinite focus state of the optical system of the 5th embodiment. Figure 10 (B) of FIG. 5 is a graph of each aberration in a closest focus distance focus state (photographic magnification β = -1.0) of the optical system of the 5th embodiment. As is apparent from the graph of each aberration, the optical system of the 5th embodiment corrects each aberration well in the entire region from the infinite focus state to the closest focus distance focus state, and has excellent imaging performance.

[0295] Next, a table of [Conditional Expression Correspondence Values] is shown below. In this table, values corresponding to each conditional expression (1) to (20) are shown for all embodiments (1st to 5th embodiments).

[0296] Conditional Expression (1) 0.20 < DG4 / TL < 0.40

[0297] Conditional Expression (2) 3.00 < (LnR2 + LnR1) / (LnR2 - LnR1) < 5.00

[0298] Conditional Expression (3) 0.75 < f1 / (-f2) < 1.30

[0299] Conditional Expression (4) 1.80 < ndM1

[0300] Conditional Expression (5) νdM1 < 26.00

[0301] Conditional Expression (6) θgFM1 - (0.6415 - 0.00162 x νdM1) < 0.0120

[0302] Conditional expression (7) 0.75 < f1 / f3 < 1.20

[0303] Conditional expression (8) 0.45 < (-β)

[0304] Conditional expression (9) 35.0 < β2 / β3 < 350.0

[0305] Conditional expression (10) 0.005 < β3 / β2 < 0.035

[0306] Conditional expression (11) {β2 + (1 / β2)} -2 <0.10

[0307] Conditional expression (12) {β3 + (1 / β3)} -2 <0.10

[0308] Conditional expression (13) 0.05 < Bf / TL < 0.35

[0309] Conditional expression (14) 0.10 < Bf / f < 0.50

[0310] Conditional expression (15) 0.50 < L1S / SLn < 1.00

[0311] Conditional expression (16) 0.70 < Mf2 / Mf3 < 1.10

[0312] Conditional expression (17) 1.80 < ndM3

[0313] Conditional expression (18) νdM3 < 26.00

[0314] Conditional expression (19) θgFM3 - (0.6415 - 0.00162 x νdM3) < 0.0120 Conditional expression (20) (L1R2 + L1R1) / (L1R2 - L1R1) < 0.10

[0315] [Conditional expression correspondence value] (1st to 3rd embodiments)

[0316]

[0317]

[0318] [Conditional expression correspondence value] (4th to 5th embodiments)

[0319]

[0320] According to the above-described embodiments, an optical system having less aberration variation at the time of focusing can be realized.

[0321] The above-described embodiments show a specific example of the present application, and the present application is not limited to these.

[0322] The following can be appropriately adopted within a range that does not impair the optical performance of the optical system of the present embodiment.

[0323] Although a 4-group structure is shown as an example of the optical system of the present embodiment, the present application is not limited thereto, and an optical system of another group structure (for example, 5 groups, etc.) can also be constituted. Specifically, a structure in which a lens or a lens group is added to the most object side or the most image surface side of the optical system of the present embodiment can also be adopted. In addition, the lens group indicates a portion having at least one lens that is separated by an air gap that changes when focusing is performed.

[0324] It can also be a lens group that moves with a component in a direction perpendicular to the optical axis or rotates and moves (wobbles) in a direction in the plane containing the optical axis, thereby correcting image blur generated by hand shake.

[0325] The lens surface can be formed by a spherical surface or a plane, or can be formed by an aspherical surface. In the case where the lens surface is a spherical surface or a plane, lens processing and assembly adjustment become easy, and deterioration of the optical performance caused by errors in the processing and assembly adjustment is prevented, and thus is preferable. In addition, deterioration of the performance is also less in the case where the image surface is shifted, and thus is preferable.

[0326] In the case where the lens surface is an aspherical surface, the aspherical surface can be any one of an aspherical surface based on lapping processing, a glass mold casting aspherical surface in which glass is formed into an aspherical shape by a mold, or a complex aspherical surface in which resin is formed into an aspherical shape on the surface of glass. In addition, the lens surface can be a diffractive surface, and the lens can be a refractive index distribution type lens (GRIN lens) or a plastic lens.

[0327] Although the aperture stop is preferably arranged between the 2nd lens group and the 3rd lens group, a member serving as the aperture stop can not be provided, and the function thereof can be replaced by the frame of the lens.

[0328] On each lens surface, an antireflection film having high transmittance in a wide wavelength region can also be applied in order to reduce glare and ghosting and achieve optical performance with high contrast.

[0329] Explanation of Reference Numerals

[0330] G1 1st lens group G2 2nd lens group

[0331] G3 3rd lens group G4 4th lens group

[0332] I image surface S aperture stop

Claims

1. An optical system, wherein the optical system is composed of a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, which are arranged in this order from an object side along an optical axis, when focusing from an infinite distance object to a close distance object, the second lens group moves toward an image side along the optical axis, the third lens group moves toward an object side along the optical axis, the interval between the adjacent lens groups changes, and the first lens group and the fourth lens group are fixed in position relative to an image plane when focusing, the optical system satisfies the following conditional expression: 0.20 < DG4 / TL < 0.40 35.0<β2 / β3<350.0 wherein DG4 is a length on the optical axis of the fourth lens group, TL is a total length of the optical system in an infinite focus state, β2 is a transverse magnification of the second lens group in the infinite focus state, β3 is a transverse magnification of the third lens group in the infinite focus state.

2. An optical system, wherein the optical system is composed of a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, which are arranged in this order from an object side along an optical axis, when focusing from an infinite distance object to a close distance object, the second lens group moves toward an image side along the optical axis, the third lens group moves toward an object side along the optical axis, the interval between the adjacent lens groups changes, and the first lens group and the fourth lens group are fixed in position relative to an image plane when focusing, the optical system satisfies the following conditional expression: 3.00 < (LnR2 + LnRl) / (LnR2 - LnRl) < 5.00 35.0<β2 / β3<350.0 wherein LnRl is a radius of curvature of an object side lens surface in a negative lens disposed at the most image side of the optical system, LnR2 is a radius of curvature of an image side lens surface in the negative lens disposed at the most image side of the optical system, β2 is a transverse magnification of the second lens group in the infinite focus state, β3 is a transverse magnification of the third lens group in the infinite focus state.

3. An optical system, wherein the optical system is composed of a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, which are arranged in this order from an object side along an optical axis, when focusing from an infinite distance object to a close distance object, the second lens group moves toward an image side along the optical axis, the third lens group moves toward an object side along the optical axis, the interval between the adjacent lens groups changes, and the first lens group and the fourth lens group are fixed in position relative to an image plane when focusing, the optical system satisfies the following conditional expression: 0.75 < f1 / (-f2) < 1.30 35.0<β2 / β3<350.0 wherein f1 is a focal length of the first lens group, f2 is a focal length of the second lens group, β2 is a transverse magnification of the second lens group in the infinite focus state, β3 is a transverse magnification of the third lens group in the infinite focus state.

4. An optical system, wherein the optical system is composed of a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, which are arranged in this order from an object side along an optical axis, when focusing from an infinite distance object to a close distance object, the second lens group moves toward an image side along the optical axis, the third lens group moves toward an object side along the optical axis, the interval between the adjacent lens groups changes, and the first lens group and the fourth lens group are fixed in position relative to an image plane when focusing, the optical system satisfies the following conditional expression: 35.0<β2 / β3<350.0 where β2: lateral magnification of the second lens group in an infinite distance focus state, β3: lateral magnification of the third lens group in an infinite distance focus state, the first lens group has a negative lens satisfying the following conditional expression: 1.80 < ndMl νdMl < 26.00 θgFMl - (0.6415 - 0.00162 x νdMl) < 0.0120 where ndMl: refractive index of d-line of the negative lens of the first lens group, νdMl: Abbe number of the negative lens of the first lens group, θgFMl: relative partial dispersion of the negative lens of the first lens group, which is defined by the following expression when the refractive index of g-line of the negative lens of the first lens group is assumed to be ngMl, the refractive index of F-line of the negative lens of the first lens group is assumed to be nFMl, and the refractive index of C-line of the negative lens of the first lens group is assumed to be nCMl, that is, θgFMl = (ngMl - nFMl) / (nFMl - nCMl).

5. The optical system according to any one of claims 2 to 4, wherein the optical system satisfies the following conditional expression: 0.20 < DG4 / TL < 0.40 where DG4: length on the optical axis of the fourth lens group, TL: total length of the optical system in an infinite distance focus state.

6. The optical system according to claim 3 or 4, wherein the optical system satisfies the following conditional expression: 3.00 < (LnR2 + LnRl) / (LnR2 - LnRl) < 5.00 where LnRl: curvature radius of an object side lens surface in a negative lens disposed at the most image side of the optical system, LnR2: curvature radius of an image side lens surface in a negative lens disposed at the most image side of the optical system.

7. The optical system according to claim 4, wherein the optical system satisfies the following conditional expression: 0.75 < f1 / (-f2) < 1.30 where f1: focal length of the first lens group, f2: focal length of the second lens group.

8. The optical system according to any one of claims 1 to 4, wherein the optical system satisfies the following conditional expression: 0.75 < f1 / f3 < 1.20 where f1: focal length of the first lens group, f3: focal length of the third lens group.

9. The optical system according to any one of claims 1 to 4, wherein the optical system satisfies the following conditional expression: 0.45<(-β) where β: lateral magnification of the optical system.

10. The optical system according to any one of claims 1 to 4, wherein the optical system satisfies the following conditional expression: 0.005<β3 / β2<0.035 β2: lateral magnification of the second lens group in an infinite focus state, 11. The optical system according to any one of claims 1 to 4, wherein The optical system satisfies the following conditional expression: {β2+(1 / β2)} -2 <0.10 β2: lateral magnification of the second lens group in an infinite focus state.

12. The optical system according to any one of claims 1 to 4, wherein The optical system satisfies the following conditional expression: {β3+(1 / β3)} -2 <0.10 β3: lateral magnification of the third lens group in an infinite focus state.

13. The optical system according to any one of claims 1 to 4, wherein The optical system satisfies the following conditional expression: 0.05 < Bf / TL < 0.35 Bf: back focus of the optical system in an infinite focus state, TL: total length of the optical system in an infinite focus state.

14. The optical system according to any one of claims 1 to 4, wherein The optical system satisfies the following conditional expression: 0.10 < Bf / f < 0.50 Bf: back focus of the optical system in an infinite focus state, f: focal length of the optical system.

15. The optical system according to any one of claims 1 to 4, wherein The optical system has an aperture, The optical system satisfies the following conditional expression: 0.50 < L1S / SLn < 1.00 L1S: distance on an optical axis from a lens surface on the most object side of the optical system to the aperture in an infinite focus state, SLn: distance on an optical axis from the aperture to a lens surface on the most image side of the optical system in an infinite focus state.

16. The optical system according to any one of claims 1 to 4, wherein The optical system satisfies the following conditional expression: 0.70 < Mf2 / Mf3 < 1.10 Mf2: absolute value of moving amount of the second lens group when focusing from an infinite object to a closest focus distance object, Mf3: absolute value of moving amount of the third lens group when focusing from an infinite object to a closest focus distance object.

17. The optical system according to any one of claims 1 to 4, wherein The third lens group has a negative lens satisfying the following conditional expression: 1.80 < ndM3 νdM3 < 26.00 θgFM3 - (0.6415 - 0.00162 x νdM3) < 0.0120 ndM3: refractive index of the negative lens of the third lens group with respect to d-line, νdM3: Abbe number of the negative lens of the third lens group, θgFM3: relative partial dispersion of the negative lens of the third lens group, which is defined by the following expression when a refractive index of the negative lens of the third lens group with respect to g-line is ngM3, a refractive index of the negative lens of the third lens group with respect to F-line is nFM3, and a refractive index of the negative lens of the third lens group with respect to C-line is nCM3, that is, θgFM3 = (ngM3 - nFM3) / (nFM3 - nCM3).

18. The optical system according to any one of claims 1 to 4, wherein The optical system satisfies the following conditional expression: (L1R2+L1R1) / (L1R2-L1R1) < 0.10 L1R1: radius of curvature of an object side lens surface in a positive lens disposed at the most object side of the optical system, L1R2: radius of curvature of an image side lens surface in a positive lens disposed at the most object side of the optical system.

19. The optical system according to any one of claims 1 to 4, wherein the lens disposed at the most image side of the fourth lens group has a negative refractive power.

20. An optical apparatus configured to be provided with the optical system according to any one of claims 1 to 19.

Images