JP2017161846A - Optical system, optical instrument and method for manufacturing optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system (wide angle lens) that is small and bright.SOLUTION: An optical system WL includes a front group G1 having a positive or negative refractive power and a rear group G2 having a positive refractive power, in which upon focusing, an interval between the front group G1 and the rear group G2 varies. The front group G1 includes an object side lens (first negative lens L11), an intermediate lens (a first positive lens L12 and a positive cemented lens consisting of a second negative lens L13 and a second positive lens L14), and an image side lens (second negative lens L15). A positive lens L24 is disposed on a side closest to an image of the rear group G2; an aperture diaphragm S is disposed in the front group G1 or the rear group G2; and the optical system satisfies a conditional expression of 0.90<φL1/φSt<1.95, where φL1 represents an effective diameter of the object side lens of the front group G1, and φSt represents an aperture diameter of the aperture diaphragm S.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical system, an optical apparatus using the optical system, and a method for manufacturing the optical system.

  2. Description of the Related Art Conventionally, an optical system that is small and has a short overall length has been proposed as an optical system that is used in an optical apparatus such as a digital still camera or a digital video camera (see, for example, Patent Document 1). However, if the total length of the optical system is shortened, the position of the exit pupil becomes closer to the image plane, and so-called shading may occur in which the substantial aperture efficiency decreases at the periphery of the image plane.

JP 2013-195558 A

  The optical system according to the present invention has a front group and a rear group arranged in order from the object side, and the distance between the front group and the rear group changes during focusing, and the front group is An object side lens having a negative refractive power, an intermediate lens, and an image side lens having a negative refractive power, which are arranged in order from the object side, and the intermediate lens is either a positive lens or a positive cemented lens The positive lens is arranged on the most image side of the rear group, and the aperture stop is arranged in the front group or the rear group, and the following conditional expression is satisfied.

0.90 <φL1 / φSt <1.95
Where φL1: effective diameter of the object side lens of the front group,
φSt: The aperture diameter of the aperture stop.

  An optical apparatus according to the present invention is configured by mounting the above optical system.

An optical system manufacturing method according to the present invention is a method for manufacturing an optical system having a front group and a rear group, which are arranged in order from the object side, and in focusing, between the front group and the rear group The interval changes, and the front group includes an object side lens having a negative refractive power, an intermediate lens, and an image side lens having a negative refractive power, which are arranged in order from the object side. It consists of one or both of a positive lens and a positive cemented lens, a positive lens is disposed closest to the image side of the rear group, an aperture stop is disposed in the front group or the rear group, and the following conditional expression Each lens is arranged in a lens barrel so as to be satisfied.
0.90 <φL1 / φSt <1.95
Where φL1: effective diameter of the object side lens of the front group,
φSt: The aperture diameter of the aperture stop.

It is a figure which shows the lens structure of the optical system which concerns on 1st Example of this embodiment. FIG. 2A is a diagram illustrating various aberrations when the optical system according to the first example is focused at infinity, and FIG. 2B is a diagram illustrating various aberrations when the optical system according to the first example is focused at a short distance. FIG. It is a figure which shows the lens structure of the optical system which concerns on 2nd Example of this embodiment. FIG. 4A is a diagram showing various aberrations when the optical system according to the second example is focused at infinity, and FIG. 4B is a diagram showing various aberrations when the optical system according to the second example is focused at a short distance. FIG. It is a figure which shows the lens structure of the optical system which concerns on 3rd Example of this embodiment. FIG. 6A is a diagram illustrating various aberrations when the optical system according to the third example is focused at infinity, and FIG. 6B is a diagram illustrating various aberrations when the optical system according to the third example is focused at a short distance. FIG. It is a figure which shows the lens structure of the optical system which concerns on 4th Example of this embodiment. FIG. 8A is a diagram showing various aberrations when the optical system according to the fourth example is focused at infinity, and FIG. 8B is a diagram showing various aberrations when the optical system according to the fourth example is focused at a short distance. FIG. It is a figure which shows the lens structure of the optical system which concerns on 5th Example of this embodiment. FIG. 10A is a diagram showing various aberrations when the optical system according to the fifth example is focused at infinity, and FIG. 10B is a diagram showing various aberrations when the optical system according to the fifth example is focused at a short distance. FIG. It is a figure which shows the lens structure of the optical system which concerns on 6th Example of this embodiment. 12A is a diagram showing various aberrations when the optical system according to the sixth example is focused at infinity, and FIG. 12B is a diagram showing various aberrations when the optical system according to the sixth example is focused at a short distance. FIG. It is a figure which shows the lens structure of the optical system which concerns on the 7th Example of this embodiment. FIG. 14A is a diagram showing various aberrations when the optical system according to the seventh example is focused at infinity, and FIG. 14B is a diagram showing various aberrations when focusing on the short distance of the optical system according to the seventh example. FIG. It is a figure which shows the structure of the camera provided with the optical system which concerns on this embodiment. It is a flowchart which shows the manufacturing method of the optical system which concerns on this embodiment.

  Hereinafter, the optical system and the optical apparatus of the present embodiment will be described with reference to the drawings. As an example of the optical system (wide-angle lens) WL according to this embodiment, the optical system WL (1) shown in FIG. 1 includes a front group G1 and a rear group G2, which are arranged in order from the object side. The The front group G1 includes an object side lens having negative refractive power, an intermediate lens, and an image side lens having negative refractive power, which are arranged in order from the object side. The intermediate lens is composed of one or both of a positive lens and a positive cemented lens. A positive lens is disposed on the most image side of the rear group G2, and an aperture stop S is disposed in the front group G1 or the rear group G2. In such an optical system WL (1), the distance between the front group G1 and the rear group G2 changes during focusing.

  The optical system WL according to the present embodiment may be the optical system WL (2) shown in FIG. 3, the optical system WL (3) shown in FIG. 5, or the optical system WL (4) shown in FIG. 9 may be the optical system WL (5) shown in FIG. 11, the optical system WL (6) shown in FIG. 11, or the optical system WL (7) shown in FIG. In addition, each group of the optical systems WL (2) to WL (7) shown in FIGS. 3, 5, 7, 9, 11, and 13 is the same as the optical system WL (1) shown in FIG. Configured.

  As described above, in the optical system WL according to the present embodiment, the front group G1 includes an object side lens having a negative refractive power, an intermediate lens (a positive lens or a positive cemented lens) having a positive refractive power, This is a reverse triplet type lens structure composed of an image side lens having negative refractive power. With this configuration, effective aberration correction can be performed, and a small and bright optical system can be obtained. Specifically, the object-side lens of the front group G1 contributes to shortening the overall length of the optical system and correcting distortion. The intermediate lens (positive lens or positive cemented lens) in the front group G1 contributes to ensuring the brightness of the optical system. The image side lens in the front group G1 contributes to correction of Petzval sum. Further, since the positive lens is arranged on the most image side of the rear group G2, the Petzval sum can be corrected well, and the position of the exit pupil sufficiently separated from the image plane I can be secured. become.

  Under the above configuration, the optical system WL according to the present embodiment satisfies the following conditional expression (1).

0.90 <φL1 / φSt <1.95 (1)
Where φL1: effective diameter of the object side lens in the front group G1,
φSt: The aperture diameter of the aperture stop S.

  Conditional expression (1) is a conditional expression for defining an appropriate range between the effective diameter of the object-side lens of the front group G1 and the aperture diameter of the aperture stop S. The aperture diameter of the aperture stop S is the diameter of the opening in the state where the aperture stop S is most open (open stop). By satisfying conditional expression (1), the position of the entrance pupil can be displaced toward the object side, so that the angle of view of the optical system WL can be widened without increasing the aperture of the front group G1. .

  If the corresponding value of the conditional expression (1) exceeds the upper limit value, the diameter of the front group G1 becomes large and the lens barrel becomes large, so that it is difficult to correct off-axis aberrations such as distortion. Further, since the aperture diameter of the aperture stop S is too small, a bright optical system cannot be obtained, which is not preferable. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (1) is preferably 1.88, and more preferably 1.75.

  If the corresponding value of conditional expression (1) is less than the lower limit value, the effective diameter of the object-side lens in the front group G1 is too small, and it becomes difficult to widen the angle of view of the optical system WL. In addition, it becomes difficult to ensure a sufficient amount of light. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (1) is preferably 0.92, and more preferably 0.94.

  The optical system WL of the present embodiment preferably satisfies the following conditional expression (2).

1.50 <ndLz + (0.002 × νdLz) <1.86 (2)
Where ndLz: refractive index with respect to d-line of the image-side lens of the front group G1,
νdLz: Abbe number of the image-side lens in the front group G1.

  Conditional expression (2) is a conditional expression for defining an appropriate range of the refractive index and Abbe number for the d-line of the image-side lens of the front group G1. By satisfying conditional expression (2), the Petzval sum can be corrected well even if the optical system WL has a wide angle of view. By disposing the image side lens of the front group G1 at a position away from the aperture stop S, it is possible to satisfactorily correct coma.

  If the corresponding value of conditional expression (2) exceeds the upper limit value, correction of Petzval sum becomes difficult, which is not preferable. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (2) is preferably 1.82, and more preferably 1.78.

  If the corresponding value of conditional expression (2) is less than the lower limit, it is not preferable because correction of Petzval sum becomes difficult. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (2) is preferably 1.58, and more preferably 1.60.

  The optical system WL of the present embodiment preferably satisfies the following conditional expression (3).

0.60 <(− Exp) / TL <1.10 (3)
Where Exp: the distance on the optical axis from the image plane I to the position of the exit pupil in the optical system WL,
TL: Distance on the optical axis from the lens surface closest to the object side to the image plane in the optical system WL in an infinitely focused state, and the air conversion distance from the lens surface closest to the image side to the image plane.

  Conditional expression (3) is a conditional expression for defining an appropriate range between the total length of the optical system WL and the distance from the image plane I to the position of the exit pupil. The distance from the image plane I to the position of the exit pupil is a positive value in the direction from the object side to the image side with the image plane I as a reference. If the corresponding value of conditional expression (3) exceeds the upper limit value, the position of the exit pupil is too far away from the image plane I toward the object side, which makes correction of field curvature difficult and undesirably increasing the size of the entire optical system. . In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (3) may preferably be set to 1.05.

  When the corresponding value of conditional expression (3) is below the lower limit, the position of the exit pupil is close to the image plane I, which is advantageous for downsizing the optical system. However, since the ray angle on the exit side becomes too acute, vignetting occurs on the image plane I side and so-called shading occurs. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (3) is preferably 0.65, and more preferably 0.70.

  In the optical system WL of the present embodiment, it is preferable that the rear group G2 has a positive refractive power and satisfies the following conditional expression (4).

0.36 <f2 / TL <1.00 (4)
Where f2 is the focal length of the rear group G2,
TL: Distance on the optical axis from the lens surface closest to the object side to the image plane in the optical system WL in an infinitely focused state, and the air conversion distance from the lens surface closest to the image side to the image plane.

  Conditional expression (4) is a conditional expression for defining an appropriate range between the focal length of the rear group G2 and the total length of the optical system WL. By satisfying conditional expression (4), high optical performance can be obtained while minimizing the total length of the optical system WL.

  If the corresponding value of the conditional expression (4) exceeds the upper limit value, the total length of the optical system WL is too short, so that it is difficult to correct sagittal coma aberration, curvature of field, and the like. Further, since the power (refractive power) of the rear group G2 is too weak, it is impossible to earn a magnification necessary for focusing. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (4) is preferably 0.95, and more preferably 0.90.

  If the corresponding value of conditional expression (4) is below the lower limit value, the total length of the optical system WL becomes long, and the entire optical system becomes large, which is not preferable. Further, since the power of the rear group G2 is too strong, it is difficult to correct spherical aberration and coma. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (4) is preferably 0.38, and more preferably 0.40.

  The optical system WL of the present embodiment preferably satisfies the following conditional expression (5).

0.38 <f / TL <0.70 (5)
Where f: focal length of the optical system WL in focus at infinity,
TL: Distance on the optical axis from the lens surface closest to the object side to the image plane in the optical system WL in an infinitely focused state, and the air conversion distance from the lens surface closest to the image side to the image plane.

  Conditional expression (5) is a conditional expression for defining an appropriate range between the total length of the optical system WL and the focal length. If the corresponding value of the conditional expression (5) exceeds the upper limit value, the total length of the optical system WL is too short, and various aberrations such as coma aberration are observed in the entire range from the infinitely focused state to the short-range focused state. It becomes difficult to correct well. In addition, it becomes difficult to correct image plane fluctuations due to focusing. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (5) is preferably 0.68, and more preferably 0.67.

  If the corresponding value of the conditional expression (5) is less than the lower limit value, the total length of the optical system WL becomes long, so that the diameter of the front group G1 becomes large and it becomes difficult to correct off-axis aberrations. Further, since the focal length is too short with respect to the entire length of the optical system WL, the focal length of each group becomes short, and it becomes difficult to correct coma and spherical aberration. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (5) is preferably set to 0.40, and more preferably to 0.42.

  The optical system WL of the present embodiment preferably satisfies the following conditional expression (6).

−0.36 <f / f1 <0.60 (6)
Where f: focal length of the optical system WL in focus at infinity,
f1: Focal length of the front group G1.

  Conditional expression (6) is a conditional expression for defining an appropriate range of power (refractive power) of the front group G1. The front group G1 preferably has a relatively weak positive or negative refractive power. If the corresponding value of conditional expression (6) exceeds the upper limit value, the focal length of the front group G1 is too long, which makes it difficult to reduce the size of the optical system. In addition, the load on the rear group G2 becomes relatively large, and it becomes difficult to correct coma and distortion. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (6) is preferably 0.59, and more preferably 0.58.

  If the corresponding value of conditional expression (6) is less than the lower limit value, the focal length of the optical system WL is too long, and it becomes difficult to widen the angle of view of the optical system WL. In addition, since the negative power of the front group G1 is too strong, it is difficult to correct lateral chromatic aberration and coma. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (6) is preferably −3.30, and more preferably −3.10.

  In the optical system WL of the present embodiment, it is preferable that the rear group G2 has a positive refractive power and satisfies the following conditional expression (7).

0.010 <f2 / | f1 | <0.900 (7)
Where f2 is the focal length of the rear group G2,
f1: Focal length of the front group G1.

  Conditional expression (7) is a conditional expression for defining an appropriate power distribution (refractive power distribution) between the front group G1 and the rear group G2. If the corresponding value of conditional expression (7) exceeds the upper limit value, the power of the front group G1 is too strong, and it becomes difficult to suppress aberration fluctuations when focusing on a short distance. Further, since the Abbe number of the lens in the front group G1 tends to be small, it is difficult to correct chromatic aberration. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (7) is preferably 0.87, and more preferably 0.84.

  When the corresponding value of conditional expression (7) is below the lower limit value, the power of the rear group G2 is too strong, and it becomes difficult to correct spherical aberration, coma aberration, and the like. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (7) is preferably 0.020, and more preferably 0.035.

  The optical system WL of the present embodiment preferably satisfies the following conditional expression (8).

0.35 <Y / BL <0.80 (8)
Y: radius of the image circle of the optical system WL,
BL: Distance on the optical axis from the most object-side lens surface to the most image-side lens surface in the infinitely focused optical system WL.

  Conditional expression (8) is a conditional expression for defining an appropriate range between the radius of the image circle of the optical system WL (that is, the maximum image height) and the lens thickness. If the corresponding value of conditional expression (8) exceeds the upper limit value, the lens configuration is thin with respect to the format size of the image sensor, but it becomes difficult to correct various aberrations. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (8) is preferably 0.70, and more preferably 0.66.

  If the corresponding value of conditional expression (8) is less than the lower limit value, the maximum image height of the optical system WL becomes small, and vignetting occurs in the peripheral light flux. Further, since it is necessary to arrange a power and a lens to reduce the incident height of off-axis rays, it is difficult to correct curvature of field, distortion, etc. as a result, which is not preferable. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (8) is preferably 0.39, more preferably 0.43.

  The optical apparatus according to the present embodiment includes the optical system WL having the above-described configuration. As a specific example, a camera (optical apparatus) provided with the optical system WL will be described with reference to FIG. The camera 1 is a digital camera provided with the optical system WL according to the above-described embodiment as a photographing lens 2 as shown in FIG. In the camera 1, light from an object (subject) (not shown) is collected by the photographing lens 2 and reaches the image sensor 3. Thereby, the light from the subject is picked up by the image pickup device 3 and recorded as a subject image in a memory (not shown). In this way, the photographer can shoot the subject with the camera 1. The camera 1 may be a mirrorless camera or a single lens reflex camera having a quick return mirror. Further, the camera 1 is not limited to a single-lens reflex type camera in which the lens barrel and the camera body main body are detachable. Even if the lens barrel and the camera body main body are an integrated compact type camera. Good. According to such a configuration, by mounting the optical system WL as a photographing lens, effective aberration correction can be performed, and a small and bright optical device can be obtained.

  Next, the method for manufacturing the above-described optical system WL will be outlined with reference to FIG. First, the front group G1 and the rear group G2 are arranged in order from the object side in the lens barrel (step ST1). At this time, the front group G1 is configured to include an object side lens having a negative refractive power, an intermediate lens, and an image side lens having a negative refractive power, which are arranged in order from the object side. At this time, the intermediate lens is configured to include either one or both of a positive lens and a positive cemented lens. At this time, the positive lens is disposed on the most image side of the rear group G2, and the aperture stop S is disposed in the front group G1 or the rear group G2. And in the case of focusing, it comprises so that the space | interval of front group G1 and back group G2 may change (step ST2). Further, each lens is arranged in the lens barrel so as to satisfy at least the conditional expression (1) (step ST3). According to such a manufacturing method, effective aberration correction can be performed, and a small and bright optical system can be manufactured.

  Hereinafter, an optical system (wide angle lens) WL according to an example of the present embodiment will be described with reference to the drawings. 1, FIG. 3, FIG. 5, FIG. 7, FIG. 9, FIG. 11 and FIG. 13 show the configurations and refractive powers of the optical systems WL {WL (1) to WL (7)} according to the first to seventh embodiments. It is sectional drawing which shows distribution. Each cross-sectional view describes the position of each group (along with “infinity” and “near distance”) when focusing from infinity to a near object.

  1, FIG. 3, FIG. 5, FIG. 7, FIG. 9, FIG. 11 and FIG. 13, each group is represented by a combination of symbol G and a number, and each lens is represented by a combination of symbol L and a number. In this case, in order to prevent complications due to an increase in the types and numbers of codes and numbers, the lens groups and the like are represented using combinations of codes and numbers independently for each embodiment. For this reason, even if the combination of the same code | symbol and number is used between Examples, it does not mean that it is the same structure.

Tables 1 to 7 are shown below. Of these, Table 1 is the first example, Table 2 is the second example, Table 3 is the third example, Table 4 is the fourth example, and Table 5 is the first. 5 Example, Table 6 is a table | surface which shows each item data in 6th Example and Table 7 in 7th Example. In each embodiment, the d-line (
Wavelength λ = 587.6 nm) and g-line (wavelength λ = 435.8 nm) are selected.

  In the [Overall Specifications] table, f indicates the focal length of the entire system in the optical system WL in the infinitely focused state, and FNO indicates the F number. 2ω represents an angle of view (the unit is ° (degree), ω is a half angle of view), and Y represents an image height (maximum image height). Bf represents the air-converted distance (back focus) on the optical axis from the lens surface closest to the image side to the image plane I in the optical system WL in the infinite focus state, and TL in the optical system WL in the infinite focus state. The distance (full length) on the optical axis from the lens surface closest to the object side to the image plane I is shown. In TL, the distance from the lens surface closest to the image side to the image plane I in the optical system WL indicates an air conversion distance. In addition, the values of TL and Bf are shown for the infinite focus state and the short distance (closest distance) focus state in [variable interval data] described later.

  ΦL1 indicates the effective diameter of the object side lens of the front group G1, and φSt indicates the aperture diameter of the aperture stop S. Exp represents the distance on the optical axis from the image plane I to the position of the exit pupil in the optical system WL in the infinitely focused state. The distance from the image plane I to the position of the exit pupil is a positive value in the direction from the object side to the image side with the image plane I as a reference. BL indicates the distance on the optical axis from the most object side lens surface to the most image side lens surface in the infinitely focused optical system WL.

In the table of [lens specifications], the surface number indicates the order of the optical surfaces from the object side along the light traveling direction, and R indicates the radius of curvature of each optical surface (the surface where the center of curvature is located on the image side). D is a positive value), D is a surface interval which is a distance on the optical axis from each optical surface to the next optical surface (or image surface), νd is an Abbe number based on the d-line of the material of the optical member, nd indicates the refractive index of the optical member material with respect to the d-line. The curvature radius “∞” indicates a plane or an aperture, and (aperture S) indicates the aperture aperture S. The description of the refractive index of air nd = 1.0000 is omitted. When the lens surface is an aspherical surface, the surface number is marked with * and the radius of curvature R column indicates the paraxial radius of curvature.

In the [Aspherical Data] table, the shape of the aspherical surface shown in [Lens Specifications] is shown by the following equation (a). X (y) is the distance along the optical axis direction from the tangential plane at the apex of the aspheric surface to the position on the aspheric surface at height y (zag amount), and R is the radius of curvature of the reference sphere (paraxial curvature radius) , Κ is the conic constant, and Ai is the i-th aspherical coefficient. “E-n” indicates “× 10 ⁻ⁿ ”. For example, 1.234E-05 = 1.234 × 10 ⁻⁵ . The secondary aspheric coefficient A2 is 0, and the description thereof is omitted.

X (y) = (y ² / R) / {1+ (1−κ × y ² / R ² ) ^1/2 } + A4 × y ⁴ + A6 × y ⁶ + A8 × y ⁸ + A10 × y ¹⁰ (a )

  In the table of [Group Data], the start surfaces (most object side surfaces) and focal lengths of the front group G1 and the rear group G2 are shown.

  The table of [variable distance data] shows the surface distance Di to the next surface in the surface number i in which the surface distance is “variable” in the table indicating [lens specifications]. For example, in the first embodiment, surface intervals D10 and D17 at surface numbers 10 and 17 are shown. These values are shown for the infinite focus state and the short distance (closest distance) focus state, respectively.

  The table corresponding to the conditional expressions (1) to (8) shows values corresponding to the conditional expressions (1) to (8).

  Hereinafter, in all the specification values, “mm” is generally used for the focal length f, curvature radius R, surface distance D, and other lengths, etc. unless otherwise specified, but the optical system is proportionally enlarged. Alternatively, the same optical performance can be obtained even by proportional reduction, and the present invention is not limited to this.

  The explanation of the table so far is common to all the embodiments, and the duplicate explanation below will be omitted.

(First embodiment)
A first embodiment will be described with reference to FIGS. FIG. 1 is a diagram illustrating a lens configuration of an optical system according to a first example of the present embodiment. The optical system WL (1) according to the first example includes a front group G1 having a positive refractive power and a rear group G2 having a positive refractive power, which are arranged in order from the object side. The sign (+) or (−) attached to the symbol of each group indicates the refractive power of each group, and this is the same in all the following examples.

  The front group G1 includes, in order from the object side, a biconcave first negative lens L11, a biconvex first positive lens L12, an aperture stop S, and a biconcave second negative lens. The lens includes a cemented lens including L13 and a biconvex second positive lens L14, and a meniscus third negative lens L15 having a convex surface facing the image side. The third negative lens L15 has an aspheric lens surface on the image side. In the first example, the first negative lens L11 corresponds to the object side lens of the present embodiment, and the third negative lens L15 corresponds to the image side lens of the present embodiment. Further, the first positive lens L12 and the positive cemented lens including the second negative lens L13 and the second positive lens L14 correspond to the intermediate lens of the present embodiment.

  The rear group G2 includes, in order from the object side, a cemented lens including a biconvex first positive lens L21 and a biconcave first negative lens L22, and a biconcave second negative lens L23. And a biconvex second positive lens L24. The second positive lens L24 has an aspheric lens surface on the image side.

  An image plane I is disposed on the image side of the rear group G2. A low pass for cutting a spatial frequency higher than the limit resolution of an image pickup device (for example, CCD, CMOS, etc.) disposed on the image plane I in the vicinity of the image plane I between the rear group G2 and the image plane I. A filter FL is arranged. In the optical system WL (1) according to the first example, when focusing from infinity to a short distance object, the front group G1 and the rear group G2 move toward the object side along the optical axis with different movement amounts. The interval between the group G1 and the rear group G2 is configured to change (become larger).

  Table 1 below lists values of specifications of the optical system according to the first example.

(Table 1)
[Overall specifications]
f = 24.97
FNO = 1.85
2ω = 62.1
Y = 14.25
Bf = 14.318
TL = 44.678
φL1 = 14.80
φSt = 14.30
Exp = -39.973
BL = 30.360
[Lens specifications]
Surface number R D νd nd
1 -23.5865 1.0000 41.51 1.575010
2 32.5087 0.9332
3 20.7551 3.5088 40.66 1.883000
4 -45.6852 1.0000
5 ∞ 2.0111 (Aperture S)
6 -30.3720 0.8000 32.18 1.672700
7 15.9804 3.7857 40.66 1.883000
8 -34.7764 1.0000
9 -23.1553 0.8000 31.16 1.688930
10 * -100.1049 D10 (variable)
11 34.2710 5.2717 40.66 1.883000
12 -13.3880 0.8000 32.18 1.672700
13 31.6442 3.9709
14 -16.5099 0.8000 33.72 1.647690
15 104.7860 0.1000
16 62.8584 4.2211 40.10 1.851348
17 * -21.0915 D17 (variable)
18 ∞ 2.0000 63.88 1.516800
19 ∞ 0.1000
[Aspherical data]
10th surface κ = 1.0000
A4 = 7.09969E-05, A6 = 5.82420E-08, A8 = 3.73981E-09, A10 = -1.74407E-11
Surface 17 κ = 1.0000
A4 = 3.72602E-05, A6 = -2.34539E-08, A8 = 1.32257E-09, A10 = -6.49301E-12
[Group data]
Group Start surface Focal length
G1 1 57.97
G2 11 34.64
[Variable interval data]
Infinite focus state Short range focus state
f = 24.97 β = −0.1
D0 ∞ 263.17
D10 0.358 1.090
D17 12.899 15.281
Bf (air) 14.318 16.700
TL (air) 44.678 47.792
[Conditional expression values]
Conditional expression (1) φL1 / φSt = 1.035
Conditional expression (2) ndLz + (0.002 × νdLz) = 1.751
Conditional expression (3) (−Exp) /TL=0.895
Conditional expression (4) f2 / TL = 0.775
Conditional expression (5) f / TL = 0.559
Conditional expression (6) f / f1 = 0.431
Conditional expression (7) f2 / | f1 | = 0.598
Conditional expression (8) Y / BL = 0.469

FIG. 2A is a diagram illustrating various aberrations of the optical system according to the first example when focusing on infinity. In each aberration diagram of FIG. 2A, FNO represents an F number, and A represents a half angle of view. The spherical aberration diagram shows the F-number value corresponding to the maximum aperture, the astigmatism diagram and the distortion diagram show the maximum half field angle, and the lateral aberration diagram shows the half field angle value. FIG. 2B is a diagram of various aberrations when the optical system according to Example 1 is in focus at a short distance (closest distance). In each aberration diagram of FIG. 2B, NA represents the numerical aperture, and H0 represents the object height. The spherical aberration diagram shows the numerical aperture value corresponding to the maximum aperture, the astigmatism diagram and the distortion diagram show the maximum object height, and the lateral aberration diagram shows the value of each object height. 2A and 2B, d indicates the d-line (wavelength λ = 587.6 nm), and g indicates the g-line (wavelength λ = 435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the aberration diagrams of the following examples, the same reference numerals as those in this example are used, and redundant description is omitted.

  From the respective aberration diagrams, it can be seen that the optical system according to the first example has excellent imaging performance by satisfactorily correcting various aberrations.

(Second embodiment)
2nd Example is described using FIGS. 3-4 and Table 2. FIG. FIG. 3 is a diagram illustrating a lens configuration of an optical system according to the second example of the present embodiment. The optical system WL (2) according to the second example includes a front group G1 having a positive refractive power and a rear group G2 having a positive refractive power arranged in order from the object side.

  The front group G1 includes a meniscus first negative lens L11 having a convex surface facing the object side, a biconvex positive lens L12, and a biconcave second negative lens L13 arranged in order from the object side. And a cemented lens. In the second example, the first negative lens L11 corresponds to the object side lens of the present embodiment, and the second negative lens L13 corresponds to the image side lens of the present embodiment. The positive lens L12 corresponds to the intermediate lens of the present embodiment.

  The rear group G2 includes an aperture stop S, a cemented lens including a biconvex first positive lens L21 and a biconcave first negative lens L22, and a biconcave second, which are arranged in order from the object side. The negative lens L23 and a biconvex second positive lens L24, and a biconvex third positive lens L25. The first positive lens L21 has an aspheric lens surface on the object side. The second negative lens L23 has an aspheric lens surface on the object side. The second positive lens L24 has an aspheric lens surface on the image side.

  An image plane I is disposed on the image side of the rear group G2. A low pass for cutting a spatial frequency higher than the limit resolution of an image pickup device (for example, CCD, CMOS, etc.) disposed on the image plane I in the vicinity of the image plane I between the rear group G2 and the image plane I. A filter FL is arranged. In the optical system WL (2) according to the second example, the front group G1 and the rear group G2 move toward the object side along the optical axis with different amounts of movement when focusing from infinity to a short distance object. The interval between the group G1 and the rear group G2 is configured to change (become larger).

  Table 2 below lists values of specifications of the optical system according to the second example.

(Table 2)
[Overall specifications]
f = 31.56
FNO = 2.20
2ω = 47.4
Y = 14.00
Bf = 22.645
TL = 47.455
φL1 = 14.35
φSt = 13.23
Exp = -40.370
BL = 24.810
[Lens specifications]
Surface number R D νd nd
1 59.8248 0.8040 70.32 1.487490
2 14.4329 0.3274
3 16.3422 4.8625 49.26 1.743200
4 -36.6404 0.7989 41.51 1.575010
5 27.5371 D5 (variable)
6 ∞ 0.2959
7 * 16.6614 2.5633 40.10 1.851348
8 -39.9032 0.8000 30.13 1.698950
9 16.3607 5.0395
10 * -12.0711 0.8000 31.16 1.688930
11 30.6678 2.2782 40.10 1.851348
12 * -24.1100 1.0000
13 96.5352 3.2292 40.66 1.883000
14 -41.0451 D14 (variable)
15 ∞ 2.0000 64.17 1.516800
16 ∞ 0.1000
[Aspherical data]
Surface 7 κ = 1.0000
A4 = -2.21170E-05, A6 = -1.02561E-07, A8 = -3.74746E-09, A10 = 1.54704E-11
10th surface κ = 1.0000
A4 = 4.14903E-04, A6 = 1.73676E-06, A8 = -6.05789E-08, A10 = 7.26224E-10
12th surface κ = 1.0000
A4 = 2.36538E-04, A6 = 3.42662E-07, A8 = -1.74584E-08, A10 = 1.51803E-10
[Group data]
Group Start surface Focal length
G1 1 200.03
G2 6 32.96
[Variable interval data]
Infinite focus state Short range focus state
f = 31.56 β = −0.1
D0 ∞ 336.06
D5 2.011 5.900
D14 21.226 24.343
Bf (air) 22.645 25.762
TL (air) 47.455 54.460
[Conditional expression values]
Conditional expression (1) φL1 / φSt = 1.085
Conditional expression (2) ndLz + (0.002 × νdLz) = 1.658
Conditional expression (3) (−Exp) /TL=0.851
Conditional expression (4) f2 / TL = 0.695
Conditional expression (5) f / TL = 0.665
Conditional expression (6) f / f1 = 0.158
Conditional expression (7) f2 / | f1 | = 0.165
Conditional expression (8) Y / BL = 0.564

  FIG. 4A is a diagram illustrating various aberrations of the optical system according to Example 2 when focused on infinity. FIG. 4B is a diagram illustrating various aberrations when the optical system according to Example 2 is in focus at a short distance (closest distance). From the respective aberration diagrams, it can be seen that the optical system according to the second example has excellent imaging performance by properly correcting various aberrations.

(Third embodiment)
A third embodiment will be described with reference to FIGS. FIG. 5 is a diagram showing a lens configuration of an optical system according to the third example of the present embodiment. The optical system WL (3) according to the third example includes a front group G1 having negative refractive power and a rear group G2 having positive refractive power, which are arranged in order from the object side.

  The front group G1 includes a meniscus first negative lens L11 having a convex surface facing the object side, a biconvex positive lens L12, and a biconcave second negative lens L13 arranged in order from the object side. And a cemented lens. The first negative lens L11 has an aspheric lens surface on the image side. In the third example, the first negative lens L11 corresponds to the object side lens of the present embodiment, and the second negative lens L13 corresponds to the image side lens of the present embodiment. The positive lens L12 corresponds to the intermediate lens of the present embodiment.

  The rear group G2 includes a meniscus first positive lens L21 having a convex surface facing the object side, an aperture stop S, and a meniscus second positive lens having a convex surface facing the image side, which are arranged in order from the object side. The lens includes a cemented lens including L22 and a biconcave negative lens L23, a biconvex third positive lens L24, and a biconvex fourth positive lens L25.

  An image plane I is disposed on the image side of the rear group G2. A low pass for cutting a spatial frequency higher than the limit resolution of an image pickup device (for example, CCD, CMOS, etc.) disposed on the image plane I in the vicinity of the image plane I between the rear group G2 and the image plane I. A filter FL is arranged. In the optical system WL (3) according to the third example, the front group G1 is fixed and the rear group G2 moves toward the object side along the optical axis when focusing from infinity to a close object. The interval between the front group G1 and the rear group G2 changes (becomes smaller).

  Table 3 below lists values of specifications of the optical system according to the third example.

(Table 3)
[Overall specifications]
f = 24.39
FNO = 1.88
2ω = 65.8
Y = 14.75
Bf = 23.457
TL = 54.380
φL1 = 18.00
φSt = 13.60
Exp = -39.982
BL = 30.923
[Lens specifications]
Surface number R D νd nd
1 36.4497 0.8205 46.96 1.540720
2 * 12.6655 4.4502
3 16.2009 3.3476 40.66 1.883000
4 -169.8361 0.8036 52.20 1.517420
5 13.3262 D5 (variable)
6 31.7481 1.6864 40.66 1.883000
7 887.1077 1.0201
8 ∞ 1.7251 (Aperture S)
9 -23.1046 5.1591 47.86 1.757000
10 -9.0050 0.8936 28.38 1.728250
11 44.1254 0.6575
12 522.8176 2.2171 40.66 1.883000
13 -22.7113 2.3118
14 343.2013 1.9337 40.66 1.883000
15 -47.0785 D15 (variable)
16 ∞ 2.0000 63.88 1.516800
17 ∞ 0.1000
[Aspherical data]
Second side κ = 1.0000
A4 = 1.10390E-05, A6 = -7.99130E-08, A8 = 1.98740E-09, A10 = -1.77630E-11
[Group data]
Group Start surface Focal length
G1 1 -210.40
G2 6 24.16
[Variable interval data]
Infinite focus state Short range focus state
f = 24.39 β = −0.1
D0 ∞ 252.46
D5 3.897 1.394
D15 22.038 24.541
Bf (air) 23.457 25.960
TL (air) 54.380 54.380
[Conditional expression values]
Conditional expression (1) φL1 / φSt = 1.324
Conditional expression (2) ndLz + (0.002 × νdLz) = 1.622
Conditional expression (3) (−Exp) /TL=0.735
Conditional expression (4) f2 / TL = 0.444
Conditional expression (5) f / TL = 0.449
Conditional expression (6) f / f1 = -0.116
Conditional expression (7) f2 / | f1 | = 0.115
Conditional expression (8) Y / BL = 0.477

  FIG. 6A is a diagram of various aberrations of the optical system according to the third example when focusing on infinity. FIG. 6B is a diagram of various aberrations when the optical system according to Example 3 is in focus at a short distance (closest distance). From the respective aberration diagrams, it can be seen that the optical system according to the third example has excellent imaging performance by properly correcting various aberrations.

(Fourth embodiment)
A fourth embodiment will be described with reference to FIGS. 7 to 8 and Table 4. FIG. FIG. 7 is a diagram showing a lens configuration of an optical system according to the fourth example of the present embodiment. The optical system WL (4) according to the fourth example includes a front group G1 having negative refractive power and a rear group G2 having positive refractive power, which are arranged in order from the object side.

  The front group G1 includes a meniscus first negative lens L11 having a convex surface facing the object side, a biconvex positive lens L12, and a biconcave second negative lens L13 arranged in order from the object side. And a cemented lens. The first negative lens L11 has an aspheric lens surface on the image side. In the fourth example, the first negative lens L11 corresponds to the object side lens of the present embodiment, and the second negative lens L13 corresponds to the image side lens of the present embodiment. The positive lens L12 corresponds to the intermediate lens of the present embodiment.

  The rear group G2 includes a meniscus first positive lens L21 having a convex surface facing the object side, an aperture stop S, and a meniscus second positive lens having a convex surface facing the image side, which are arranged in order from the object side. The lens includes a cemented lens including L22 and a biconcave negative lens L23, a meniscus third positive lens L24 having a convex surface facing the image side, and a biconvex fourth positive lens L25.

  An image plane I is disposed on the image side of the rear group G2. A low pass for cutting a spatial frequency higher than the limit resolution of an image pickup device (for example, CCD, CMOS, etc.) disposed on the image plane I in the vicinity of the image plane I between the rear group G2 and the image plane I. A filter FL is arranged. In the optical system WL (4) according to the fourth example, the front group G1 is fixed and the rear group G2 moves to the object side along the optical axis when focusing from infinity to a close object. The interval between the front group G1 and the rear group G2 changes (becomes smaller).

  Table 4 below provides values of specifications of the optical system according to the fourth example.

(Table 4)
[Overall specifications]
f = 24.01
FNO = 1.71
2ω = 67.4
Y = 14.75
Bf = 22.577
TL = 54.340
φL1 = 20.00
φSt = 13.80
Exp = -40.008
BL = 31.763
[Lens specifications]
Surface number R D νd nd
1 39.9359 1.0000 61.25 1.589130
2 * 14.3824 4.7333
3 15.7804 5.0881 40.66 1.883000
4 -44.4075 0.8082 38.03 1.603420
5 13.3628 D5 (variable)
6 22.1593 1.8601 40.66 1.883000
7 66.7019 0.3806
8 ∞ 2.9573 (Aperture S)
9 -17.2370 2.9736 55.35 1.677900
10 -9.1895 0.8017 27.57 1.755200
11 60.0458 0.9320
12 -123.7762 2.6605 40.66 1.883000
13 -19.0508 0.2421
14 72.9743 3.1748 42.73 1.834810
15 -39.1454 D15 (variable)
16 ∞ 2.0000 63.88 1.516800
17 ∞ 0.1000
[Aspherical data]
Second side κ = 1.0000
A4 = 1.21050E-05, A6 = 2.10680E-08, A8 = 1.53200E-10, A10 = 2.64730E-12
[Group data]
Group Start surface Focal length
G1 1 -499.56
G2 6 23.43
[Variable interval data]
Infinite focus state Short range focus state
f = 24.01 β = −0.1
D0 ∞ 244.78
D5 4.151 1.733
D15 21.158 23.576
Bf (air) 22.577 24.995
TL (air) 54.340 54.340
[Conditional expression values]
Conditional expression (1) φL1 / φSt = 1.449
Conditional expression (2) ndLz + (0.002 × νdLz) = 1.679
Conditional expression (3) (−Exp) /TL=0.636
Conditional expression (4) f2 / TL = 0.431
Conditional expression (5) f / TL = 0.442
Conditional expression (6) f / f1 = -0.048
Conditional expression (7) f2 / | f1 | = 0.047
Conditional expression (8) Y / BL = 0.464

  FIG. 8A is a diagram of various aberrations of the optical system according to Example 4 when focused on infinity. FIG. 8B is a diagram of various aberrations when the optical system according to Example 4 is in focus at a short distance (closest distance). From the respective aberration diagrams, it can be seen that the optical system according to the fourth example has excellent imaging performance by satisfactorily correcting various aberrations.

(5th Example)
A fifth embodiment will be described with reference to FIGS. 9 to 10 and Table 5. FIG. FIG. 9 is a diagram illustrating a lens configuration of an optical system according to Example 5 of the present embodiment. The optical system WL (5) according to the fifth example includes a front group G1 having negative refractive power and a rear group G2 having positive refractive power, which are arranged in order from the object side.

  The front group G1 includes a meniscus first negative lens L11 having a convex surface facing the object side, a biconvex positive lens L12, and a biconcave second negative lens L13 arranged in order from the object side. And a cemented lens. The first negative lens L11 has an aspheric lens surface on the image side. In the fifth example, the first negative lens L11 corresponds to the object side lens of the present embodiment, and the second negative lens L13 corresponds to the image side lens of the present embodiment. The positive lens L12 corresponds to the intermediate lens of the present embodiment.

The rear group G2 includes a meniscus first positive lens L21 having a convex surface facing the object side, an aperture stop S, and a meniscus second positive lens having a convex surface facing the image side, which are arranged in order from the object side. L
22 and a biconcave negative lens L23, a meniscus third positive lens L24 having a convex surface facing the image side, and a biconvex fourth positive lens L25.

  An image plane I is disposed on the image side of the rear group G2. A low pass for cutting a spatial frequency higher than the limit resolution of an image pickup device (for example, CCD, CMOS, etc.) disposed on the image plane I in the vicinity of the image plane I between the rear group G2 and the image plane I. A filter FL is arranged. In the optical system WL (5) according to the fifth example, the front group G1 is fixed and the rear group G2 moves to the object side along the optical axis when focusing from infinity to a close object. The interval between the front group G1 and the rear group G2 changes (becomes smaller).

  Table 5 below lists values of specifications of the optical system according to the fifth example.

(Table 5)
[Overall specifications]
f = 23.47
FNO = 2.25
2ω = 66.9
Y = 14.75
Bf = 23.557
TL = 49.428
φL1 = 18.00
φSt = 11.41
Exp = -40.109
BL = 25.871
[Lens specifications]
Surface number R D νd nd
1 107.9731 0.8205 46.97 1.540720
2 * 10.9981 2.4243
3 13.9894 2.5274 46.59 1.816000
4 -79.8057 0.8000 52.20 1.517420
5 15.0985 D5 (variable)
6 26.2360 1.3840 40.66 1.883000
7 197.2957 1.3232
8 ∞ 4.9853 (Aperture S)
9 -24.8310 2.5295 60.19 1.640000
10 -7.7839 0.8000 31.16 1.688930
11 58.9890 0.6647
12 -74.9679 1.6834 40.66 1.883000
13 -19.5144 0.1292
14 509.9112 1.7993 40.66 1.883000
15 -31.4185 D15 (variable)
16 ∞ 2.0000 63.88 1.516800
17 ∞ 0.1000
[Aspherical data]
Second side κ = 1.0000
A4 = -1.23248E-07, A6 = -3.78341E-09, A8 = -2.50622E-09, A10 = -4.53602E-12
[Group data]
Group Start surface Focal length
G1 1 -83.16
G2 6 22.47
[Variable interval data]
Infinite focus state Short range focus state
f = 23.47 β = -0.1
D0 ∞ 249.95
D5 4.000 1.355
D15 22.139 24.784
Bf (air) 23.557 26.202
TL (air) 49.428 49.428
[Conditional expression values]
Conditional expression (1) φL1 / φSt = 1.578
Conditional expression (2) ndLz + (0.002 × νdLz) = 1.622
Conditional expression (3) (−Exp) /TL=0.911
Conditional expression (4) f2 / TL = 0.455
Conditional expression (5) f / TL = 0.475
Conditional expression (6) f / f1 = −0.282
Conditional expression (7) f2 / | f1 | = 0.270
Conditional expression (8) Y / BL = 0.570

  FIG. 10A is a diagram of various aberrations of the optical system according to Example 5 when focusing on infinity. FIG. 10B is a diagram illustrating various aberrations when the optical system according to Example 5 is in focus at a short distance (closest distance). From each aberration diagram, it can be seen that the optical system according to the fifth example has excellent imaging performance by satisfactorily correcting various aberrations.

(Sixth embodiment)
A sixth embodiment will be described with reference to FIGS. 11 to 12 and Table 6. FIG. FIG. 11 is a diagram showing a lens configuration of an optical system according to the sixth example of the present embodiment. The optical system WL (6) according to the sixth example includes a front group G1 having a positive refractive power and a rear group G2 having a positive refractive power, which are arranged in order from the object side.

  The front group G1 includes a biconcave first negative lens L11, a biconvex positive lens L12, and a meniscus second negative lens L13 having a convex surface facing the image side, which are arranged in order from the object side. And a cemented lens. In the sixth example, the first negative lens L11 corresponds to the object side lens of the present embodiment, and the second negative lens L13 corresponds to the image side lens of the present embodiment. The positive lens L12 corresponds to the intermediate lens of the present embodiment.

  The rear group G2 includes an aperture stop S, a cemented lens including a biconvex first positive lens L21 and a biconcave first negative lens L22, and a biconcave second, which are arranged in order from the object side. The negative lens L23 and a biconvex second positive lens L24, and a biconvex third positive lens L25. The first positive lens L21 has an aspheric lens surface on the object side. The second negative lens L23 has an aspheric lens surface on the object side. The second positive lens L24 has an aspheric lens surface on the image side.

  An image plane I is disposed on the image side of the rear group G2. A low pass for cutting a spatial frequency higher than the limit resolution of an image pickup device (for example, CCD, CMOS, etc.) disposed on the image plane I in the vicinity of the image plane I between the rear group G2 and the image plane I. A filter FL is arranged. In the optical system WL (6) according to the sixth example, the front group G1 and the rear group G2 move toward the object side along the optical axis with different amounts of movement when focusing from infinity to a short distance object. The interval between the group G1 and the rear group G2 is configured to change (become small).

  Table 6 below provides values of specifications of the optical system according to the sixth example.

(Table 6)
[Overall specifications]
f = 24.10
FNO = 1.85
2ω = 65.1
Y = 14.75
Bf = 14.943
TL = 39.463
φL1 = 14.00
φSt = 13.00
Exp = -39.971
BL = 24.520
[Lens specifications]
Surface number R D νd nd
1 -28.4741 0.8923 41.51 1.575010
2 39.1920 0.4983
3 16.9984 3.0364 40.66 1.883000
4 -42.5726 0.7889 31.16 1.688930
5 -1010.0926 D5 (variable)
6 ∞ 3.2962 (Aperture S)
7 * 24.3876 3.6900 40.10 1.851350
8 -10.9999 0.8108 30.13 1.698950
9 16.8961 3.5031
10 * -7.7846 0.7999 31.16 1.688930
11 98.8713 2.7021 40.10 1.851350
12 * -14.9932 0.1008
13 154.0868 3.0786 40.66 1.883000
14 -27.6738 D14 (variable)
15 ∞ 2.0000 63.88 1.516800
16 ∞ 0.1000
[Aspherical data]
Surface 7 κ = 1.0000
A4 = -1.13520E-04, A6 = -6.74260E-07, A8 = -2.01520E-08, A10 = 9.39710E-11
10th surface κ = 1.0000
A4 = 5.79240E-04, A6 = 3.88230E-06, A8 = -2.06270E-08, A10 = 1.30200E-09
12th surface κ = 1.0000
A4 = 2.30750E-04, A6 = -1.71840E-08, A8 = -5.02940E-09, A10 = 4.73930E-12
[Group data]
Group Start surface Focal length
G1 1 42.30
G2 6 34.37
[Variable interval data]
Infinite focus state Short range focus state
f = 24.10 β = −0.1
D0 ∞ 250.63
D5 1.322 1.200
D14 13.525 15.970
Bf (air) 14.943 17.388
TL (air) 39.463 41.785
[Conditional expression values]
Conditional expression (1) φL1 / φSt = 1.077
Conditional expression (2) ndLz + (0.002 × νdLz) = 1.751
Conditional expression (3) (−Exp) /TL=1.014
Conditional expression (4) f2 / TL = 0.871
Conditional expression (5) f / TL = 0.611
Conditional expression (6) f / f1 = 0.570
Conditional expression (7) f2 / | f1 | = 0.803
Conditional expression (8) Y / BL = 0.602

  FIG. 12A is a diagram of various aberrations of the optical system according to Example 6 when focused on infinity. FIG. 12B is a diagram illustrating various aberrations when the optical system according to Example 6 is in focus at a short distance (closest distance). From each aberration diagram, it can be seen that the optical system according to Example 6 has excellent imaging performance by correcting various aberrations satisfactorily.

(Seventh embodiment)
A seventh embodiment will be described with reference to FIGS. 13 to 14 and Table 7. FIG. FIG. 13 is a diagram showing a lens configuration of an optical system according to the seventh example of the present embodiment. The optical system WL (7) according to the seventh example includes a front group G1 having a positive refractive power and a rear group G2 having a positive refractive power, which are arranged in order from the object side.

  The front group G1 includes, in order from the object side, a biconcave first negative lens L11, a biconvex first positive lens L12, an aperture stop S, and a biconcave second negative lens. The lens includes a cemented lens including L13 and a biconvex second positive lens L14, and a biconcave third negative lens L15. The first negative lens L11 has an aspheric lens surface on the object side. The third negative lens L15 has an aspheric lens surface on the object side. In the seventh example, the first negative lens L11 corresponds to the object side lens of the present embodiment, and the third negative lens L15 corresponds to the image side lens of the present embodiment. Further, the first positive lens L12 and the positive cemented lens including the second negative lens L13 and the second positive lens L14 correspond to the intermediate lens of the present embodiment.

  The rear group G2 includes a cemented lens including a biconvex first positive lens L21 and a biconcave first negative lens L22, a biconcave second negative lens L23, The lens includes a cemented lens including a biconvex second positive lens L24 and a meniscus third positive lens L25 having a convex surface facing the image side. The third positive lens L25 has an aspheric lens surface on the image side.

  An image plane I is disposed on the image side of the rear group G2. A low pass for cutting a spatial frequency higher than the limit resolution of an image pickup device (for example, CCD, CMOS, etc.) disposed on the image plane I in the vicinity of the image plane I between the rear group G2 and the image plane I. A filter FL is arranged. In the optical system WL (7) according to the seventh example, the front group G1 and the rear group G2 move toward the object side along the optical axis with different movement amounts when focusing from infinity to a short distance object. The interval between the group G1 and the rear group G2 is configured to change (become small).

  Table 7 below provides values of specifications of the optical system according to the seventh example.

(Table 7)
[Overall specifications]
f = 35.79
FNO = 1.86
2ω = 62.0
Y = 21.60
Bf = 19.756
TL = 56.084
φL1 = 19.20
φSt = 20.00
Exp = -40.000
BL = 36.328
[Lens specifications]
Surface number R D νd nd
1 * -40.1205 1.250 31.2 1.68893
2 54.9934 0.125
3 25.9110 3.722 40.7 1.88300
4 -132.1071 1.250
5 ∞ 1.956 (Aperture S)
6 -66.3010 1.000 41.0 1.58144
7 20.2021 4.306 40.7 1.88300
8 -77.5553 0.439
9 * -62.6081 1.250 31.2 1.68893
10 114.3743 D10 (variable)
11 30.5815 4.417 40.7 1.88300
12 -34.7670 1.251 36.4 1.62004
13 35.1617 5.121
14 -16.5664 1.000 30.1 1.69895
15 47.2983 5.005 40.7 1.88300
16 -35.9354 0.500
17 -53.1146 1.867 49.5 1.77250
18 * -29.4890 D18 (variable)
19 ∞ 2.500 63.9 1.51680
20 ∞ 0.100
[Aspherical data]
First side κ = 1.0000
A4 = 2.17830E-07, A6 = 2.28154E-08, A8 = -1.79806E-10, A10 = 8.74643E-13
9th surface κ = 1.0000
A4 = -2.16812E-05, A6 = 4.81264E-09, A8 = 1.34488E-10, A10 = 2.15929E-13
18th surface κ = 1.0000
A4 = 2.16108E-05, A6 = 3.37861E-08, A8 = 1.21515E-10, A10 = -3.44430E-13
[Group data]
Group Start surface Focal length
G1 1 79.95
G2 11 50.83
[Variable interval data]
Infinite focus state Short range focus state
f = 35.79 β = −0.2162
D0 ∞ 186.16
D10 1.868 0.902
D18 18.008 25.874
Bf (air) 19.756 27.622
TL (air) 56.084 62.984
[Conditional expression values]
Conditional expression (1) φL1 / φSt = 0.960
Conditional expression (2) ndLz + (0.002 × νdLz) = 1.751
Conditional expression (3) (−Exp) /TL=0.878
Conditional expression (4) f2 / TL = 0.893
Conditional expression (5) f / TL = 0.629
Conditional expression (6) f / f1 = 0.448
Conditional expression (7) f2 / | f1 | = 0.636
Conditional expression (8) Y / BL = 0.595

  FIG. 14A is a diagram of various aberrations of the optical system according to Example 7 when focused on infinity. FIG. 14B is a diagram illustrating various aberrations when the optical system according to Example 7 is in focus at a short distance (closest distance). From the respective aberration diagrams, it can be seen that the optical system according to the seventh example has excellent imaging performance by properly correcting various aberrations.

  According to each of the embodiments described above, an optical system that is small and has good optical performance can be realized.

  Here, each said Example has shown one specific example of this invention, and this invention is not limited to these.

  Note that the following contents can be adopted as appropriate as long as the optical performance of the optical system of the present embodiment is not impaired.

  As a numerical example of the optical system of the present embodiment, a two-group configuration including a front group and a rear group has been shown, but the present application is not limited to this, and an optical system having other group configurations (for example, three groups). Can also be configured. Specifically, a configuration in which a lens or a lens group is added to the most object side or the most image plane side of the optical system of the present embodiment may be used.

  In the optical system of the present embodiment, the lens group or the partial lens group is moved so as to have a component in a direction perpendicular to the optical axis, or is rotated and moved (oscillated) in the in-plane direction including the optical axis. An anti-vibration lens group that corrects image blur caused by blur may be used.

  The lens surface may be formed as a spherical surface, a flat surface, or an aspheric surface. When the lens surface is a spherical surface or a flat surface, lens processing and assembly adjustment are facilitated, and optical performance deterioration due to errors in processing and assembly adjustment can be prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance.

  When the lens surface is an aspheric surface, the aspheric surface is an aspheric surface by grinding, a glass mold aspheric surface made of glass with an aspheric shape, or a composite aspheric surface made of resin with an aspheric shape on the glass surface. Either is fine. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

The aperture stop may be replaced by a lens frame without providing a member as an aperture stop.

  Each lens surface may be provided with an antireflection film having a high transmittance in a wide wavelength region in order to reduce flare and ghost and achieve high contrast optical performance. Thereby, flare and ghost can be reduced, and high optical performance with high contrast can be achieved.

G1 Front group G2 Rear group I Image surface S Aperture stop

Claims (10)

A front group and a rear group, arranged in order from the object side,
During focusing, the distance between the front group and the rear group changes,
The front group is composed of an object side lens having a negative refractive power, an intermediate lens, and an image side lens having a negative refractive power, arranged in order from the object side.
The intermediate lens is composed of one or both of a positive lens and a positive cemented lens,
A positive lens is disposed on the most image side of the rear group,
An aperture stop is disposed in the front group or the rear group,
An optical system satisfying the following conditional expression:
0.90 <φL1 / φSt <1.95
Where φL1: effective diameter of the object side lens of the front group,
φSt: The aperture diameter of the aperture stop. The optical system according to claim 1, wherein the following conditional expression is satisfied.
1.50 <ndLz + (0.002 × νdLz) <1.86
Where ndLz: refractive index with respect to d-line of the image side lens of the front group,
νdLz: Abbe number of the image side lens in the front group. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.60 <(− Exp) / TL <1.10
Where Exp: the distance on the optical axis from the image plane in the optical system to the position of the exit pupil,
TL: Distance on the optical axis from the lens surface closest to the object side to the image plane in the optical system in the infinitely focused state, and the air-converted distance from the lens surface closest to the image side to the image plane. The rear group has a positive refractive power;
The optical system according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
0.36 <f2 / TL <1.00
Where f2: focal length of the rear group,
TL: Distance on the optical axis from the lens surface closest to the object side to the image plane in the optical system in the infinitely focused state, and the air-converted distance from the lens surface closest to the image side to the image plane. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.38 <f / TL <0.70
Where f: focal length of the optical system in the infinitely focused state,
TL: Distance on the optical axis from the lens surface closest to the object side to the image plane in the optical system in the infinitely focused state, and the air-converted distance from the lens surface closest to the image side to the image plane. The optical system according to claim 1, wherein the following conditional expression is satisfied.
−0.36 <f / f1 <0.60
Where f: focal length of the optical system in the infinitely focused state,
f1: Focal length of the front group. The rear group has a positive refractive power;
The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.010 <f2 / | f1 | <0.900
Where f2: focal length of the rear group,
f1: Focal length of the front group. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.35 <Y / BL <0.80
Where Y: radius of the image circle of the optical system,
BL: Distance on the optical axis from the most object side lens surface to the most image side lens surface in the optical system in an infinitely focused state.   An optical apparatus configured by mounting the optical system according to claim 1. A method of manufacturing an optical system having a front group and a rear group, arranged in order from the object side,
During focusing, the distance between the front group and the rear group changes,
The front group is composed of an object side lens having a negative refractive power, an intermediate lens, and an image side lens having a negative refractive power, arranged in order from the object side.
The intermediate lens is composed of one or both of a positive lens and a positive cemented lens,
A positive lens is disposed on the most image side of the rear group,
An aperture stop is disposed in the front group or the rear group,
To satisfy the following conditional expression,
A method of manufacturing an optical system, wherein each lens is arranged in a lens barrel.
0.90 <φL1 / φSt <1.95
Where φL1: effective diameter of the object side lens of the front group,
φSt: The aperture diameter of the aperture stop.

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