JP2017161848A - 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 has high optical performance while having a large aperture ratio.SOLUTION: An optical system WL includes a first lens group G1 and a second lens group G2, in which upon focusing from an infinite distance to a close distance object, the first lens group G1 is fixed while the second lens group G2 moves to the object side along the optical axis, and an interval between the first lens group G1 and the second lens group G2 varies. An aperture diaphragm S is disposed between the first lens group G1 and the second lens group G2; and a lens disposed on a side closest to an object of the second lens group G2 located on an image side of the aperture diaphragm S is a negative lens, satisfying a conditional expression of 0.10<(R22+R21)/(R22-R21)<3.00, where R21 represents a radius of curvature of a lens surface on the object side of the above negative lens, and R22 represents a radius of curvature of a lens surface on the image side of the above negative lens.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.

  Conventionally, a bright wide-angle lens suitable for wide-angle shooting has been proposed as an optical system used in optical devices such as a digital single-lens reflex camera and a digital video camera (see, for example, Patent Document 1). For example, there is a wide-angle lens in which an afocal converter is provided on the object side of a Gaussian lens configuration. However, in such an optical system, the total length and the aperture of the optical system are increased, and the entire optical system may be increased in size.

JP 2014-202952 A

  The optical system according to the present invention has a first lens group and a second lens group arranged in order from the object side, and the first lens group is fixed when focusing from infinity to a short distance object. Then, the second lens group moves to the object side along the optical axis, the interval between the first lens group and the second lens group changes, and the first lens group and the second lens group An aperture stop is disposed between them, and the lens disposed closest to the object side of the second lens group located on the image side of the aperture stop is a negative lens, and is disposed closest to the object side of the second lens group. The object-side lens surface of the negative lens is a concave surface, and satisfies the following conditional expression.

0.10 <(R22 + R21) / (R22-R21) <3.00
R21: radius of curvature of the lens surface on the object side in the negative lens arranged closest to the object side in the second lens group,
R22: radius of curvature of the image-side lens surface of the negative lens arranged closest to the object side in the second lens group.

  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 first lens group and a second lens group arranged in order from the object side, and focusing on an object at a short distance from infinity. At this time, the first lens group is fixed, the second lens group moves to the object side along the optical axis, and the distance between the first lens group and the second lens group changes, and the first lens group changes. An aperture stop is disposed between one lens group and the second lens group, and the lens disposed closest to the object side of the second lens group located on the image side of the aperture stop is a negative lens, and the second The lens surface on the object side in the negative lens disposed on the most object side of the lens group is a concave surface, and each lens is disposed in a lens barrel so as to satisfy the following conditional expression.
0.10 <(R22 + R21) / (R22-R21) <3.00
R21: radius of curvature of the lens surface on the object side in the negative lens arranged closest to the object side in the second lens group,
R22: radius of curvature of the image-side lens surface of the negative lens arranged closest to the object side in the second lens group.

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 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 the present embodiment, the optical system WL (1) shown in FIG. 1 includes a first lens group G1 and a second lens group G2 arranged in order from the object side. Configured. An aperture stop S is disposed between the first lens group G1 and the second lens group G2. The negative lens is disposed on the most object side of the second lens group G2 located on the image side of the aperture stop S. The lens surface on the object side in the negative lens disposed closest to the object side in the second lens group G2 is a concave surface. In such an optical system WL (1), when focusing from infinity to a close object, the first lens group G1 is fixed, and the second lens group G2 moves to the object side along the optical axis. The distance between the first lens group G1 and the second lens group G2 changes. With this configuration, it is possible to obtain an optical system that is small and has good optical performance while having a large aperture ratio.

  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. The optical system WL (5) shown in FIG. Each lens group of the optical systems WL (2) to WL (5) shown in FIGS. 3, 5, 7, and 9 is configured in the same manner as the optical system WL (1) shown in FIG.

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

0.10 <(R22 + R21) / (R22-R21) <3.00 (1)
R21: radius of curvature of the lens surface on the object side in the negative lens arranged closest to the object side in the second lens group G2,
R22: radius of curvature of the lens surface on the image side of the negative lens disposed closest to the object side in the second lens group G2.

  Conditional expression (1) is a conditional expression for defining an appropriate range of the shape factor of the negative lens arranged closest to the object side in the second lens group G2. The lens surface disposed on the image side of the aperture stop S includes a first lens group G1 that receives incident light with an acute angle from the off-axis, and a second lens group G2 that telecentrically arranges the light emitted from the first lens group G1. It is an important lens surface located between. Conditional expression (1) shows an appropriate shape of the negative lens disposed on the most object side of the second lens group G2 having this lens surface. In addition, since this negative lens is formed so that R21 <R22, various aberrations can be easily corrected.

  If the corresponding value of conditional expression (1) exceeds the upper limit value, the degree of meniscus of the shape of the negative lens disposed closest to the object side in the second lens group G2 is too strong, and higher order aberrations are generated. Absent. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (1) is preferably 2.90, and more preferably 2.85.

  When the corresponding value of the conditional expression (1) is below the lower limit value, the degree of directing the concave surface toward the object side of the negative lens shape arranged closest to the object side of the second lens group G2 increases, so that spherical aberration and coma aberration Correction becomes difficult. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (1) is preferably 0.20, and more preferably 0.30.

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

0.20 <f / TL <0.35 (2)
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 (2) is a conditional expression for defining an appropriate range between the focal length and the total length of the optical system WL. By satisfying conditional expression (2), it is possible to obtain good optical performance while keeping the total length of the optical system WL as small as possible.

  When the corresponding value of the conditional expression (2) exceeds the upper limit value, the total length of the optical system WL is shortened, so that it is necessary to increase the power of each group, and it becomes difficult to correct spherical aberration, coma aberration, and the like. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (2) is preferably 0.30, and more preferably 0.28.

  When the corresponding value of the conditional expression (2) is less than the lower limit value, the total length of the optical system WL becomes long, so the diameter of the negative lens of the first lens group G1 increases, and it becomes difficult to correct off-axis aberrations and chromatic aberrations. . In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (2) is preferably 0.21, and more preferably 0.23.

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

0.30 <f2 / TL <0.65 (3)
Where f2: focal length of the second lens 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 (3) is a conditional expression for defining an appropriate range between the focal length of the second lens group G2 and the total length of the optical system WL. When the corresponding value of the conditional expression (3) exceeds the upper limit value, the total length of the optical system WL is too short, and it becomes difficult to correct coma and the like. Further, since the power (refractive power) of the second lens group G2 is too weak, when the second lens group G2 is set as the focusing group, the magnification necessary for focusing cannot be obtained, and the first lens group G1 There is a risk of interference. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (3) is preferably 0.62, and more preferably 0.60.

  If the corresponding value of conditional expression (3) is less than 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 second lens group G2 is too strong, it becomes difficult to correct spherical aberration and coma. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (3) is preferably 0.35, and more preferably 0.40.

  The optical system WL of the present embodiment preferably satisfies the following conditional expression (4).

0.45 <Bf / f <0.80 (4)
Where Bf: the air-converted distance on the optical axis from the lens surface closest to the image side to the image surface in the optical system WL in an infinitely focused state,
f: Focal length of the optical system WL in an infinitely focused state.

  Conditional expression (4) is a conditional expression for defining an appropriate range between the focal length of the optical system WL and the back focus. If the corresponding value of the conditional expression (4) exceeds the upper limit value, the back focus is too long, and the telecentricity is maintained, but the entire optical system is enlarged, which is not preferable. In addition, since the focal length of each lens group is shortened, it is difficult to correct spherical aberration and coma. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (4) is preferably 0.75, and more preferably 0.68.

  When the corresponding value of the conditional expression (4) is below the lower limit value, the back focus is too short, so that a space for arranging a filter or the like cannot be secured. Further, since the position of the exit pupil is close to the image plane I, the shading becomes remarkable, and the resolution around the screen is lowered. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (4) is preferably 0.50, and more preferably 0.55.

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

0.10 <f / f1 <0.55 (5)
Where f: focal length of the optical system WL in focus at infinity,
f1: Focal length of the first lens group G1.

  Conditional expression (5) is a conditional expression for defining an appropriate range of the focal length of the first lens group G1 with respect to the focal length of the optical system WL. If the corresponding value of conditional expression (5) exceeds the upper limit value, the power (refractive power) of the first lens group G1 is too strong, and it is difficult to correct off-axis aberrations such as field curvature, astigmatism, and coma. become. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (5) is preferably 0.50, and more preferably 0.47.

  If the corresponding value of the conditional expression (5) is less than the lower limit value, the power of the first lens group G1 becomes weak and the entire optical system becomes large, which is not preferable. Further, it is not preferable because the power balance between the first lens group G1 and the second lens group G2 is lost and distortion is changed. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (5) is preferably set to 0.13, and more preferably set to 0.16.

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

0.95 <DG1 / DG2 <1.70 (6)
DG1: distance on the optical axis from the most object side lens surface to the most image side lens surface in the first lens group G1,
DG2: distance on the optical axis from the most object-side lens surface to the most image-side lens surface in the second lens group G2.

Conditional expression (6) is a conditional expression for defining an appropriate distribution between the total thickness (lens thickness) of the first lens group G1 and the total thickness of the second lens group G2. In the optical system of the type as in the present embodiment, the second lens group G2 is often responsible for focusing, so that weight reduction is required. Further, shortening the total thickness of the first lens group G1 directly leads to shortening of the lens barrel. Further, considering that there is an aperture stop S between the first lens group G1 and the second lens group G2, the exit pupil is determined from the distribution of the total thickness of the first lens group G1 and the total thickness of the second lens group G2. It is possible to guess the position.

  If the corresponding value of conditional expression (6) exceeds the upper limit value, the total thickness of the second lens group G2 is too thin, and it becomes difficult to correct spherical aberration, coma aberration, and the like. Further, since the total thickness of the second lens group G2 is too thin, it is difficult to ensure a sufficient distance from the image plane I to the position of the exit pupil. In order to ensure the effect of this embodiment, the upper limit value of conditional expression (6) is preferably 1.65, and more preferably 1.61.

  If the corresponding value of conditional expression (6) is less than the lower limit value, the total thickness of the first lens group G1 is too thin, making it difficult to correct distortion. In addition, since the total thickness of the second lens group G2 is too thick, the load on the weight of the second lens group G2 increases during focusing. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (6) is preferably set to 1.00, and more preferably set to 1.08.

  The optical system WL of the present embodiment preferably satisfies the following conditional expression (7).

-12.0 <R1b / φ1b <8.0 (7)
Where R1b: radius of curvature of the lens surface on the image side of the lens disposed closest to the image side of the first lens group G1,
φ1b: Effective diameter on the lens surface on the image side of the lens disposed closest to the image side in the first lens group G1.

  Conditional expression (7) is a conditional expression for defining an appropriate shape of the lens surface on the image side in the lens disposed closest to the image side of the first lens group G1. When the corresponding value of conditional expression (7) exceeds the upper limit value, the radius of curvature of the lens surface on the image side in the lens disposed closest to the image side in the first lens group G1 is on the plus side (the side with the convex surface facing the object side) In this case, the curvature of the lens surface becomes smaller on the plus side, making it difficult to correct spherical aberration and coma. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (7) is preferably 5.0, and more preferably 2.0.

  When the corresponding value of conditional expression (7) is below the lower limit, the radius of curvature of the lens surface on the image side of the lens disposed closest to the image side in the first lens group G1 is on the minus side (the side with the convex surface facing the image side) In this case, the curvature of the lens surface becomes smaller on the minus side, and it is difficult to correct off-axis coma and the like. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (7) is preferably −0.7, and more preferably −4.0.

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

0.10 <Y / BL <0.56 (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 the 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 is difficult to correct off-axis aberrations such as coma aberration. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (8) is preferably 0.50, and more preferably 0.40.

  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, so that a sufficient angle of view cannot be secured. In addition, it becomes difficult to correct spherical aberration and the like. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (8) is preferably 0.15, and more preferably 0.20.

  The optical system WL of the present embodiment preferably satisfies the following conditional expression (9).

0.12 <| X2 | / f <0.20 (9)
Where X2 is the amount of movement of the second lens group G2 when focusing from infinity to a close object,
f: Focal length of the optical system WL in an infinitely focused state.

  Conditional expression (9) is a conditional expression for defining an appropriate range of the amount of movement of the second lens group G2 during focusing. If the corresponding value of the conditional expression (9) exceeds the upper limit value, it is necessary to weaken the power (refractive power) of the second lens group G2, so that the optical performance during focusing on the close range cannot be kept good. This makes it difficult to correct curvature of field. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (9) is preferably 0.19, and more preferably 0.18.

  When the corresponding value of the conditional expression (9) is below the lower limit value, it is necessary to increase the power of the second lens group G2, so that it is 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 (9) is preferably set to 0.13, and more preferably to 0.14.

  The optical system WL of the present embodiment preferably satisfies the following conditional expression (10).

5.20 <Y × f / TL <6.80 (10)
Y: radius of the image circle of the optical system WL,
f: focal length of the optical system WL in an 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 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 (10) is a conditional expression for defining an appropriate range of the total length of the optical system WL with respect to the combination of the radius of the image circle and the focal length of the optical system WL. If the corresponding value of the conditional expression (10) exceeds the upper limit value, the total length of the optical system WL is shortened. Therefore, it is necessary to increase the power of each lens group, and it is difficult to correct various aberrations such as spherical aberration and coma aberration. become. In order to ensure the effect of the present embodiment, the upper limit value of conditional expression (10) is preferably 6.50, and more preferably 6.00.

  When the corresponding value of the conditional expression (10) is less than the lower limit value, the total length of the optical system WL becomes long, so the diameter of the negative lens of the first lens group G1 becomes large, and it becomes difficult to correct off-axis aberrations. In order to ensure the effect of the present embodiment, the lower limit value of conditional expression (10) is preferably 5.22, and more preferably 5.25.

  In the optical system WL of the present embodiment, it is preferable that the image-side lens surface of the lens disposed closest to the image side of the second lens group G2 is a convex surface. As a result, the Petzval sum can be appropriately corrected, and the position of the exit pupil sufficiently separated from the image plane I can be secured.

In the optical system WL of the present embodiment, it is preferable that the image-side lens surface of the lens disposed closest to the image side of the first lens group G1 is a convex surface. Thereby, it is possible to satisfactorily correct distortion, field curvature, and astigmatism.

  In the optical system WL of the present embodiment, the second lens group G2 includes a meniscus first negative lens arranged in order from the object side and having a convex surface facing the image side, and a biconvex first positive lens. The second negative lens may have a biconcave shape and the second positive lens may have a biconvex shape. As a result, coma and spherical aberration can be favorably corrected.

  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. This camera 1 is a digital camera provided with the optical system WL according to the above-described embodiment as a photographic 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 photographic lens, it is possible to obtain an optical apparatus having a small aperture and good optical performance while having a large aperture ratio.

  Next, the method for manufacturing the above-described optical system WL will be outlined with reference to FIG. First, the first lens group G1 and the second lens group G2 are arranged in order from the object side in the lens barrel (step ST1). At this time, an aperture stop S is disposed between the first lens group G1 and the second lens group G2. In addition, a negative lens is disposed closest to the object side of the second lens group G2 located on the image side of the aperture stop S, and the lens surface on the object side of the negative lens is formed to be a concave surface. When focusing from infinity to a short distance object, the first lens group G1 is fixed, the second lens group G2 moves toward the object side along the optical axis, and the first lens group G1 and the second lens group G2 The distance from the lens group G2 is changed (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, it is possible to manufacture an optical system that is small and has good optical performance while having a large aperture ratio.

  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, and FIG. 9 are cross-sectional views showing the configuration and refractive power distribution of the optical systems WL {WL (1) to WL (5)} according to the first to fifth embodiments. is there. Each cross-sectional view describes the position of each group (along with “infinity” and “near distance”) when focusing from infinity to a near object.

  In FIG. 1, FIG. 3, FIG. 5, FIG. 7, and FIG. 9, each lens 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 5 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. It is a table | surface which shows each item data in 5 Examples.
In each embodiment, d-line (wavelength λ = 587.6 nm) and g-line (wavelength λ = 435.8 nm) are selected as the aberration characteristic calculation targets.

  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.

  Φ1b represents the effective diameter of the first lens group G1 on the most image side of the first lens group G1 on the image side lens surface, and X2 represents the second lens group G2 during focusing from infinity to a close object. Indicates the amount of movement. The amount of movement X2 is positive in the direction from the object side to the image side.

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 that is the distance on the optical axis from each optical surface to the next optical surface (or image surface), nd is the refractive index of the material of the optical member with respect to d-line, and νd is optical The Abbe numbers based on the d-line of the material of the member are shown respectively. 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 [Lens Group Data], the start surfaces (most object side surfaces) and focal lengths of the first lens group G1 and the second lens 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 D7 and D19 at surface numbers 7 and 19 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 (10) shows values corresponding to the conditional expressions (1) to (10).

  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 first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side. . An aperture stop S is disposed between the first lens group G1 and the second lens group G2. The sign (+) or (-) attached to the symbol of each lens group indicates the refractive power of each lens group, and this is the same in all the following embodiments.

  The first lens group G1 is arranged in order from the object side, the meniscus first negative lens L11 having a convex surface facing the object side, the biconcave second negative lens L12, and the first biconvex first lens L12. It is composed of a cemented lens made up of a positive lens L13 and a biconvex second positive lens L14. That is, the first lens group G1 is composed of four lenses. The first negative lens L11 has an aspheric lens surface on the object side.

  The second lens group G2 includes, in order from the object side, a meniscus first negative lens L21 having a convex surface facing the image side, a biconvex first positive lens L22, and a biconvex second lens. Positive lens L23, a meniscus second negative lens L24 with a convex surface facing the object side, a meniscus third negative lens L25 with a convex surface facing the object side, and a biconvex third positive lens And a cemented lens made of L26. That is, the second lens group G2 is composed of six lenses. The first positive lens L22 has an aspheric lens surface on the image side.

  An image plane I is disposed on the image side of the second lens group G2. In order to cut a spatial frequency equal to or higher than the limit resolution of an image sensor (for example, a CCD or a CMOS) disposed on the image plane I in the vicinity of the image plane I between the second lens group G2 and the image plane I. Low pass filter FL is arranged. In the optical system WL (1) according to the first example, the first lens group G1 is fixed and the second lens group G2 is positioned on the object side along the optical axis when focusing from infinity to a short distance object. And the distance between the first lens group G1 and the second lens group G2 is changed (decreased). Further, at the time of focusing, the aperture stop S is configured to move along the optical axis together with the second lens group G2.

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

(Table 1)
[Overall specifications]
f = 24.03
FNO = 1.95
2ω = 86.2
Y = 21.60
Bf = 27.018 (air equivalent length)
TL = 98.489 (Air equivalent length)
φ1b = 25.01
X2 = -3.592
[Lens specifications]
Surface number R D nd νd
1 61.00000 1.524 1.49710 81.6
2 * 16.07881 19.148
3 -39.52997 1.000 1.72825 28.4
4 25.44383 6.899 1.90265 35.7
5 -58.29655 0.200
6 94.37151 2.095 1.95375 32.3
7 -299.84325 D7 (variable)
8 ∞ 4.568 (Aperture S)
9 -23.12889 1.000 1.72825 28.4
10 -52.88931 4.545
11 108.15411 4.892 1.95 150 29.8
12 * -91.29359 0.100
13 39.72911 4.198 1.75500 52.3
14 -42.52504 0.100
15 72.26139 3.584 1.66446 35.9
16 21.80180 2.060
17 1631.11840 1.000 1.79504 28.7
18 21.79336 4.991 1.49700 81.7
19 -37.70133 D19 (variable)
20 ∞ 1.500 1.51680 64.2
21 ∞ 0.000
[Aspherical data]
Second side κ = 7.44500E-01
A4 = -1.11688E-06, A6 = 1.89520E-08, A8 = -8.66722E-11, A10 = 1.04786E-13
12th surface κ = -1.73400E-01
A4 = 1.56371E-05, A6 = 7.15689E-09, A8 = 5.77717E-13, A10 = 3.50489E-14
[Lens group data]
Group Start surface Focal length
G1 1 141.96
G2 9 41.08
[Variable interval data]
Infinity focusing state Short-distance focusing state f = 24.03 β = -0.1474
D0 ∞ 151.00
D7 9.567 5.975
D19 25.929 29.521
Bf (air) 27.018 30.610
TL (air) 98.489 98.489
[Conditional expression values]
Conditional expression (1) (R22 + R21) / (R22-R21) = 2.55
Conditional expression (2) f / TL = 0.24
Conditional expression (3) f2 / TL = 0.41
Conditional expression (4) Bf / f = 1.12
Conditional expression (5) f / f1 = 0.17
Conditional expression (6) DG1 / DG2 = 1.17
Conditional expression (7) R1b / φ1b = -11.99
Conditional expression (8) Y / BL = 0.302
Conditional expression (9) | X2 | /f=0.15
Conditional expression (10) Y × f / TL = 5.24

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 first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side. . An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 is arranged in order from the object side, the meniscus first negative lens L11 having a convex surface facing the object side, the meniscus second negative lens L12 having a convex surface facing the object side, The lens includes a biconvex first positive lens L13 and a cemented lens including a biconcave third negative lens L14 and a biconvex second positive lens L15. That is, the first lens group G1 is composed of five lenses. The first positive lens L13 has an aspheric lens surface on the object side.

  The second lens group G2 includes a biconcave first negative lens L21 arranged in order from the object side, a meniscus first positive lens L22 having a convex surface facing the image side, and a biconvex second lens. A positive lens L23, a meniscus second negative lens L24 having a convex surface directed toward the object side, a cemented lens including a biconcave third negative lens L25 and a biconvex third positive lens L26. Is composed of. That is, the second lens group G2 is composed of six lenses. The first negative lens L21 has an aspheric lens surface on the object side. The second positive lens L23 has an aspheric image side lens surface.

  An image plane I is disposed on the image side of the second lens group G2. In order to cut a spatial frequency equal to or higher than the limit resolution of an image sensor (for example, a CCD or a CMOS) disposed on the image plane I in the vicinity of the image plane I between the second lens group G2 and the image plane I. Low pass filter FL is arranged. In the optical system WL (2) according to the second example, the first lens group G1 is fixed and the second lens group G2 is positioned on the object side along the optical axis when focusing from infinity to a close object. And the distance between the first lens group G1 and the second lens group G2 is changed (decreased). Further, at the time of focusing, the aperture stop S is configured to move along the optical axis together with the second lens group G2.

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

(Table 2)
[Overall specifications]
f = 24.09
FNO = 1.85
2ω = 85.4
Y = 21.60
Bf = 16.046 (Air equivalent length)
TL = 98.489 (Air equivalent length)
φ1b = 27.98
X2 = -4.192
[Lens specifications]
Surface number R D nd νd
1 61.00000 1.980 1.67270 32.2
2 23.15274 7.051
3 107.22972 1.000 1.66755 41.9
4 28.01217 9.439
5 * 45.38890 4.210 1.95 150 29.8
6 -240.05180 7.560
7 -49.14202 1.000 1.69895 30.1
8 35.49623 7.421 1.88300 40.7
9 -41.96879 D9 (variable)
10 ∞ 3.319 (Aperture S)
11 * -55.74290 2.391 1.84681 23.6
12 157.34103 2.383
13 -114.23645 3.509 1.80610 41.0
14 -25.00000 1.500
15 38.65454 6.108 1.77250 49.5
16 * -34.03812 0.100
17 366.29782 3.109 1.80 100 34.9
18 21.06154 3.672
19 -2295.36810 1.000 1.69895 30.1
20 23.32581 5.870 1.58913 61.2
21 -190.00000 D21 (variable)
22 ∞ 1.500 1.51680 64.2
23 ∞ 0.100
[Aspherical data]
5th surface κ = 4.61700E-01
A4 = -7.16734E-07, A6 = -1.63781E-09, A8 = 2.70647E-12, A10 = -1.86351E-14
11th surface κ = 7.55290E + 00
A4 = -3.49326E-05, A6 = -2.64640E-08, A8 = 1.07434E-10, A10 = 4.95139E-15
16th surface κ = 5.78000E-02
A4 = 1.66911E-07, A6 = 1.21571E-08, A8 = -1.13971E-11, A10 = 3.58849E-14
[Lens group data]
Group Start surface Focal length
G1 1 53.41
G2 11 52.51
[Variable interval data]
Infinite focusing state Short focusing state f = 24.09 β = -0.1448
D0 ∞ 151.00
D9 9.821 5.629
D21 14.957 19.148
Bf (air) 16.046 20.237
TL (air) 98.489 98.489
[Conditional expression values]
Conditional expression (1) (R22 + R21) / (R22-R21) = 0.48
Conditional expression (2) f / TL = 0.24
Conditional expression (3) f2 / TL = 0.53
Conditional expression (4) Bf / f = 0.67
Conditional expression (5) f / f1 = 0.45
Conditional expression (6) DG1 / DG2 = 1.34
Conditional expression (7) R1b / φ1b = -1.50
Conditional expression (8) Y / BL = 0.262
Conditional expression (9) | X2 | /f=0.17
Conditional expression (10) Y × f / TL = 5.26

  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 first lens group G1 having positive refractive power and a second lens group G2 having positive refractive power, which are arranged in order from the object side. . An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 is arranged in order from the object side, the meniscus first negative lens L11 having a convex surface facing the object side, the meniscus first positive lens L12 having a convex surface facing the object side, The lens includes a cemented lens including a meniscus second positive lens L13 having a convex surface facing the image side and a biconcave second negative lens L14, and a biconvex third positive lens L15. That is, the first lens group G1 is composed of five lenses. The first positive lens L12 has an aspheric lens surface on the image side.

  The second lens group G2 has a meniscus first negative lens L21 having a convex surface facing the image side, a biconvex first positive lens L22, and a convex surface facing the image side, which are arranged in order from the object side. A cemented lens composed of a meniscus second negative lens L23, a biconvex second positive lens L24, a biconcave third negative lens L25, and a meniscus second lens having a convex surface facing the image side. And a cemented lens including a fourth negative lens L26 having a convex surface facing the image side and a third positive lens L27 having a meniscus shape. That is, the second lens group G2 is composed of seven lenses. The second positive lens L24 has an aspheric lens surface on the image side. The third positive lens L27 has an aspheric image side lens surface.

An image plane I is disposed on the image side of the second lens group G2. In order to cut a spatial frequency equal to or higher than the limit resolution of an image sensor (for example, a CCD or a CMOS) disposed on the image plane I in the vicinity of the image plane I between the second lens group G2 and the image plane I. Low pass filter FL is arranged. In the optical system WL (3) according to the third example, the first lens group G1 is fixed and the second lens group G2 is positioned on the object side along the optical axis when focusing from infinity to a close object. And the distance between the first lens group G1 and the second lens group G2 is changed (decreased). Further, the aperture stop S is configured to be fixed together with the first lens group G1 during focusing.

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

(Table 3)
[Overall specifications]
f = 24.14
FNO = 1.85
2ω = 85.2
Y = 21.60
Bf = 16.092 (air equivalent length)
TL = 98.489 (Air equivalent length)
φ1b = 23.98
X2 = -3.954
[Lens specifications]
Surface number R D nd νd
1 103.66156 1.800 1.58913 61.2
2 20.42084 16.831
3 64.27053 1.860 1.88202 37.2
4 * 135.57264 9.763
5 -55.25307 6.230 1.80604 40.7
6 -20.58872 1.200 1.66446 35.9
7 92.74950 0.500
8 55.32621 4.140 1.80400 46.6
9 -51.80704 3.761
10 ∞ D10 (variable) (Aperture S)
11 -41.48146 2.000 1.68893 31.2
12 -87.94541 0.600
13 25.38767 7.248 1.69350 53.2
14 -26.98527 1.000 1.80 100 34.9
15 -216.57089 2.720
16 121.88390 2.962 1.82080 42.7
17 * -56.93890 1.616
18 -217.18037 2.039 1.69895 30.1
19 32.18253 5.258
20 -25.67890 1.000 1.71736 29.6
21 -188.05035 3.000 1.80610 40.7
22 * -30.00000 D22 (variable)
23 ∞ 1.500 1.51680 64.2
24 ∞ 0.000
[Aspherical data]
4th surface κ = 4.20000E + 01
A4 = 6.07770E-07, A6 = 2.82158E-11, A8 = 3.48783E-12, A10 = -1.69590E-14
17th surface κ = -8.18280E + 00
A4 = 1.15224E-05, A6 = -1.65861E-08, A8 = -1.36830E-10, A10 = 3.82021E-13
22nd surface κ = 2.41950E + 00
A4 = 2.89965E-05, A6 = 6.30910E-08, A8 = 3.81139E-10, A10 = 7.26525E-13
[Lens group data]
Group Start surface Focal length
G1 1 67.39
G2 11 56.98
[Variable interval data]
Infinite focusing state Short focusing state f = 24.14 β = -0.1469
D0 ∞ 151.00
D10 6.869 2.915
D22 15.003 18.957
Bf (air) 16.092 20.046
TL (air) 98.489 98.489
[Conditional expression values]
Conditional expression (1) (R22 + R21) / (R22-R21) = 2.79
Conditional expression (2) f / TL = 0.24
Conditional expression (3) f2 / TL = 0.58
Conditional expression (4) Bf / f = 0.67
Conditional expression (5) f / f1 = 0.36
Conditional expression (6) DG1 / DG2 = 1.57
Conditional expression (7) R1b / φ1b = -2.16
Conditional expression (8) Y / BL = 0.262
Conditional expression (9) | X2 | /f=0.16
Conditional expression (10) Y × f / TL = 5.27

  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 first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side. . An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 is arranged in order from the object side, the meniscus first negative lens L11 having a convex surface facing the object side, the meniscus second negative lens L12 having a convex surface facing the object side, The lens includes a biconvex first positive lens L13, a biconcave third negative lens L14, and a biconvex second positive lens L15. That is, the first lens group G1 is composed of five lenses. The second negative lens L12 has an aspheric lens surface on the image side.

  The second lens group G2 includes, in order from the object side, a meniscus first negative lens L21 having a convex surface facing the image side, a meniscus first positive lens L22 having a convex surface facing the image side, A biconvex second positive lens L23, a biconvex third positive lens L24, a meniscus second negative lens L25 having a convex surface facing the object side, and a meniscus having a convex surface facing the image side And a third negative lens L26 having a shape. That is, the second lens group G2 is composed of six lenses. The first positive lens L22 has an aspheric lens surface on the image side. The third positive lens L24 has an aspheric lens surface on the image side.

  An image plane I is disposed on the image side of the second lens group G2. In order to cut a spatial frequency equal to or higher than the limit resolution of an image sensor (for example, a CCD or a CMOS) disposed on the image plane I in the vicinity of the image plane I between the second lens group G2 and the image plane I. Low pass filter FL is arranged. In the optical system WL (4) according to the fourth example, the first lens group G1 is fixed and the second lens group G2 is moved along the optical axis on the object side when focusing from infinity to a close object. And the distance between the first lens group G1 and the second lens group G2 is changed (decreased). Further, at the time of focusing, the aperture stop S is configured to move along the optical axis together with the second lens group G2.

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

(Table 4)
[Overall specifications]
f = 24.09
FNO = 1.65
2ω = 85.0
Y = 21.60
Bf = 16.091 (Air equivalent length)
TL = 98.489 (Air equivalent length)
φ1b = 27.94
X2 = -3.837
[Lens specifications]
Surface number R D nd νd
1 331.20889 2.200 1.58913 61.2
2 20.26007 7.099
3 28.21954 1.000 1.69680 55.5
4 * 23.24760 6.765
5 54.21538 5.983 1.95375 32.3
6 -135.86729 2.821
7 -43.70270 1.000 1.74077 27.7
8 75.22383 0.100
9 49.75549 6.465 1.75500 52.3
10 -39.38857 D10 (variable)
11 ∞ 9.687 (Aperture S)
12 -17.89127 1.000 1.84666 23.8
13 -82.98744 0.100
14 -115.72126 4.350 1.92286 20.9
15 * -32.43919 0.200
16 158.09926 5.968 1.75 500 52.3
17 -26.81826 0.100
18 58.04640 5.240 1.58913 61.2
19 * -39.44565 0.100
20 165.11070 4.567 1.80518 25.4
21 22.03164 4.040
22 ∞ 0.931 (virtual surface)
23 -114.80353 3.000 1.48749 70.3
24 -190.00000 D24 (variable)
25 ∞ 1.500 1.51680 64.2
26 ∞ 0.100
[Aspherical data]
4th surface κ = -2.74100E-01
A4 = 8.68713E-06, A6 = -5.16406E-10, A8 = 3.46658E-12, A10 = -4.26743E-15
Surface 15 κ = -2.79540E + 00
A4 = 9.40408E-06, A6 = 2.07357E-08, A8 = -4.24422E-11, A10 = 4.51553E-14
19th surface κ = -1.16990E + 00
A4 = -2.05004E-07, A6 = 3.48317E-08, A8 = -9.42820E-11, A10 = 1.27866E-13
[Lens group data]
Group Start surface Focal length
G1 1 71.87
G2 12 42.25
[Variable interval data]
Infinite focus state Short range focus state f = 24.09 β = -0.1463
D0 ∞ 151.00
D10 9.681 5.843
D24 15.002 18.840
Bf (air) 16.091 19.929
TL (air) 98.489 98.489
[Conditional expression values]
Conditional expression (1) (R22 + R21) / (R22-R21) = 1.55
Conditional expression (2) f / TL = 0.24
Conditional expression (3) f2 / TL = 0.43
Conditional expression (4) Bf / f = 0.67
Conditional expression (5) f / f1 = 0.34
Conditional expression (6) DG1 / DG2 = 1.13
Conditional expression (7) R1b / φ1b = -1.41
Conditional expression (8) Y / BL = 0.262
Conditional expression (9) | X2 | /f=0.16
Conditional expression (10) Y × f / TL = 5.26

  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 first lens group G1 having a positive refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side. . An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

  The first lens group G1 is arranged in order from the object side, the meniscus first negative lens L11 having a convex surface facing the object side, the meniscus first positive lens L12 having a convex surface facing the object side, It is composed of a biconcave second negative lens L13 and a biconvex second positive lens L14. That is, the first lens group G1 is composed of four lenses. The second positive lens L14 has an aspheric image side lens surface.

  The second lens group G2 is arranged in order from the object side, and includes a meniscus first negative lens L21 having a convex surface facing the image side, a biconvex first positive lens L22, and a biconcave second lens. A cemented lens including the negative lens L23, a biconvex second positive lens L24, a biconcave third negative lens L25, a biconcave fourth negative lens L26, and a biconvex third And a cemented lens including the positive lens L27. That is, the second lens group G2 is composed of seven lenses. The second positive lens L24 has an aspheric lens surface on the image side. The third positive lens L27 has an aspheric image side lens surface.

  An image plane I is disposed on the image side of the second lens group G2. In order to cut a spatial frequency equal to or higher than the limit resolution of an image sensor (for example, a CCD or a CMOS) disposed on the image plane I in the vicinity of the image plane I between the second lens group G2 and the image plane I. Low pass filter FL is arranged. In the optical system WL (5) according to the fifth example, the first lens group G1 is fixed and the second lens group G2 is moved along the optical axis on the object side when focusing from infinity to a close object. And the distance between the first lens group G1 and the second lens group G2 is changed (decreased). Further, the aperture stop S is configured to be fixed together with the first lens group G1 during focusing.

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

(Table 5)
[Overall specifications]
f = 24.88
FNO = 1.85
2ω = 85.0
Y = 21.60
Bf = 16.084 (Air equivalent length)
TL = 98.489 (Air equivalent length)
φ1b = 26.32
X2 = -4.162
[Lens specifications]
Surface number R D nd νd
1 259.93798 1.800 1.61800 63.3
2 23.21609 17.645
3 57.64328 3.617 1.85026 32.4
4 825.22838 10.110
5 -34.47703 1.000 1.80518 25.4
6 537.21533 0.500
7 87.30361 5.646 1.85108 40.1
8 * -33.94300 2.539
9 ∞ D9 (variable) (Aperture S)
10 -51.86043 2.000 1.63980 34.5
11 -625.30255 0.100
12 25.00000 11.041 1.61800 63.3
13 -27.39159 1.000 1.62588 35.7
14 27.16911 0.782
15 24.68610 5.040 1.88202 37.2
16 * -127.35739 3.526
17 -866.88526 1.000 1.64769 33.7
18 37.60165 3.974
19 -29.83312 1.000 1.69895 30.1
20 108.02024 3.000 1.82098 42.5
21 * -34.70573 D21 (variable)
22 ∞ 1.500 1.51680 63.9
23 ∞ 0.100
[Aspherical data]
8th surface κ = 4.89200E-01
A4 = 8.32980E-07, A6 = 1.36681E-09, A8 = 2.95579E-12, A10 = -9.22667E-15
16th surface κ = -1.97822E + 01
A4 = 1.34043E-05, A6 = -1.68712E-08, A8 = -6.06266E-11, A10 = 1.67715E-13
21st surface κ = 1.03830E + 00
A4 = 2.78128E-05, A6 = 1.14967E-08, A8 = 6.40144E-10, A10 = -8.79238E-13
[Lens group data]
Group Start surface Focal length
G1 1 73.76
G2 10 52.78
[Variable interval data]
Infinite focus state Short range focus state f = 24.88 β = -0.1525
D0 ∞ 150.00
D9 7.119 2.916
D21 14.995 19.198
Bf (air) 16.084 20.287
TL (air) 98.489 98.489
[Conditional expression values]
Conditional expression (1) (R22 + R21) / (R22-R21) = 1.18
Conditional expression (2) f / TL = 0.31
Conditional expression (3) f2 / TL = 0.66
Conditional expression (4) Bf / f = 0.65
Conditional expression (5) f / f1 = 0.34
Conditional expression (6) DG1 / DG2 = 1.24
Conditional expression (7) R1b / φ1b = -1.31
Conditional expression (8) Y / BL = 0.262
Conditional expression (9) | X2 | /f=0.17
Conditional expression (10) Y × f / TL = 6.72

  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.

  According to each of the above embodiments, it is possible to realize an optical system having a small aperture and good optical performance while having a large aperture ratio.

  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 is shown, but the present application is not limited to this, and an optical system of another group configuration (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, not only the second lens group G2, but also a single lens group, a plurality of lens groups, or a partial lens group is moved in the optical axis direction to focus from an object at infinity to a near object. A focusing lens group may be used. This focusing lens group can be applied to autofocus, and is also suitable for driving a motor for autofocus (using an ultrasonic motor or the like).

  In addition, 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 (swayed) in the in-plane direction including the optical axis to reduce image blur caused by camera shake. A vibration-proof lens group to be corrected 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 is preferably disposed between the first lens group and the second lens group, but the role of the aperture stop may be substituted 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 First lens group G2 Second lens group I Image plane S Aperture stop

Claims (14)

Having a first lens group and a second lens group arranged in order from the object side;
When focusing from infinity to a short distance object, the first lens group is fixed, the second lens group moves to the object side along the optical axis, and the first lens group and the second lens The distance between the group changes,
An aperture stop is disposed between the first lens group and the second lens group;
The lens disposed closest to the object side of the second lens group located on the image side of the aperture stop is a negative lens.
The object-side lens surface of the negative lens disposed closest to the object side of the second lens group is a concave surface,
An optical system satisfying the following conditional expression:
0.10 <(R22 + R21) / (R22-R21) <3.00
R21: radius of curvature of the lens surface on the object side in the negative lens arranged closest to the object side in the second lens group,
R22: radius of curvature of the image-side lens surface of the negative lens arranged closest to the object side in the second lens group. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.20 <f / TL <0.35
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.
0.30 <f2 / TL <0.65
Where f2: focal length of the second lens 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 any one of claims 1 to 3, wherein the following conditional expression is satisfied.
0.45 <Bf / f <0.80
Where Bf: the air equivalent distance on the optical axis from the lens surface closest to the image side to the image plane in the optical system in the infinitely focused state,
f: Focal length of the optical system in an infinitely focused state. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.10 <f / f1 <0.55
Where f: focal length of the optical system in the infinitely focused state,
f1: Focal length of the first lens group. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.95 <DG1 / DG2 <1.70
DG1: distance on the optical axis from the most object side lens surface to the most image side lens surface in the first lens group,
DG2: Distance on the optical axis from the most object side lens surface to the most image side lens surface in the second lens group. The optical system according to claim 1, wherein the following conditional expression is satisfied.
-12.0 <R1b / φ1b <8.0
Where R1b: radius of curvature of the lens surface on the image side in the lens disposed closest to the image side of the first lens group,
φ1b: An effective diameter on the lens surface on the image side of the lens disposed closest to the image side in the first lens group. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.10 <Y / BL <0.56
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. The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.12 <| X2 | / f <0.20
Where X2 is the amount of movement of the second lens group when focusing from infinity to a close object,
f: Focal length of the optical system in an infinitely focused state. The optical system according to claim 1, wherein the following conditional expression is satisfied.
5.20 <Y × f / TL <6.80
Where Y: radius of the image circle of the optical system,
f: focal length of the optical system in an 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.   11. The optical system according to claim 1, wherein an image-side lens surface of a lens disposed closest to the image side of the second lens group is a convex surface.   The optical system according to any one of claims 1 to 11, wherein an image-side lens surface of a lens disposed closest to the image side of the first lens group is a convex surface.   An optical apparatus configured by mounting the optical system according to claim 1. A method of manufacturing an optical system having a first lens group and a second lens group, arranged in order from the object side,
When focusing from infinity to a short distance object, the first lens group is fixed, the second lens group moves to the object side along the optical axis, and the first lens group and the second lens The distance between the group changes,
An aperture stop is disposed between the first lens group and the second lens group;
The lens disposed closest to the object side of the second lens group located on the image side of the aperture stop is a negative lens.
The object-side lens surface of the negative lens disposed closest to the object side of the second lens group is a concave surface,
To satisfy the following conditional expression,
A method of manufacturing an optical system, wherein each lens is arranged in a lens barrel.
0.10 <(R22 + R21) / (R22-R21) <3.00
R21: radius of curvature of the lens surface on the object side in the negative lens arranged closest to the object side in the second lens group,
R22: radius of curvature of the image-side lens surface of the negative lens arranged closest to the object side in the second lens group.

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