JP5903937B2 - OPTICAL SYSTEM, OPTICAL DEVICE, AND OPTICAL SYSTEM MANUFACTURING METHOD - Google Patents

Description

The present invention relates to a wide-angle, large-diameter optical system that is optimal for photographing optical systems such as digital cameras, film cameras, and video cameras.

In recent years, a zoom lens of a compact digital camera has become a mainstream type in which a lens barrel is retracted in the camera when the camera is not used. Similar to a zoom lens, a fixed-focus wide-angle lens whose focal length does not change with respect to an object point at infinity has been proposed in which the lens barrel is retracted into the camera when the camera is not used (for example, (See Patent Document 1).

JP 2008-40033 A

A conventional fixed-focus wide-angle lens is small and has a wide angle of view, but Fno is as dark as about 4.0.

The present invention has been made in view of such a problem, and the lens barrel can be retracted into the camera when the camera is not used. The optical system has a small size, a wide angle of view, and a large aperture. An object of the present invention is to provide an optical apparatus and a method for manufacturing an optical system.

In order to achieve such an object, an optical system according to the present invention includes a first lens group having a negative refractive power, an aperture stop, a second lens group, which are arranged in order from the object side along the optical axis. The third lens group having a positive refractive power substantially consists of three lens groups, and the first lens group has a negative refractive power arranged in order from the object side along the optical axis. 1 lens, a second lens having negative refracting power with the object side facing the concave surface toward the object side, and a third lens, and the third lens group is a single lens having positive refracting power. It consists of a lens and satisfies the following conditional expression.

−23.0 <νd3−νd2 <24.2
fL1 / fL2 <0.2
However,
νd3: Abbe number based on the d-line of the third lens,
νd2: Abbe number based on the d-line of the second lens ,
fL1: the focal length of the first lens,
fL2: focal length of the second lens.

  The optical apparatus according to the present invention includes any one of the above-described optical systems.

The method of manufacturing an optical system according to the present invention includes a first lens group having a negative refractive power, an aperture stop, a second lens group, and a positive refractive power, which are arranged in order from the object side along the optical axis. And a third lens group having substantially three lens groups , the first lens group having negative refractive power arranged in order from the object side along the optical axis. A first lens having a negative refracting power with the object side surface facing the object side and a third lens, and the third lens group has a positive refracting power. Each lens is built into the lens barrel so that the following conditional expression is satisfied.

−23.0 <νd3−νd2 <24.2
fL1 / fL2 <0.2
However,
νd3: Abbe number based on the d-line of the third lens,
νd2: Abbe number based on the d-line of the second lens ,
fL1: the focal length of the first lens,
fL2: focal length of the second lens.

According to the present invention, it is possible to retract the lens barrel in the camera when the camera is not used, and to provide a small-sized and wide angle of view, a large-aperture optical system, an optical apparatus, and an optical system manufacturing method. can do.

It is sectional drawing which shows the structure of the optical system which concerns on 1st Example, (a) is at the time of an infinite focus ((beta) = 0.000), (b) is at the time of an intermediate distance focus ((beta) =-0.036), (c ) Indicates the arrangement when focusing on a close range (β = −0.179). FIG. 6 is a diagram illustrating various aberrations of the optical system according to Example 1, where (a) is in focus at infinity (β = 0.000), (b) is in focus at an intermediate distance (β = −0.036), and (c) is in focus. The aberration diagrams at the close focus distance (β = −0.179) are shown respectively. It is sectional drawing which shows the structure of the optical system which concerns on 2nd Example, (a) is at the time of infinity focusing ((beta) = 0.0000), (b) is at the time of intermediate distance focusing ((beta) =-0.009), (c ) Shows the arrangement when focusing on a close range (β = −0.036). FIG. 4 is a diagram illustrating various aberrations of the optical system according to Example 2, wherein (a) is in focus at infinity (β = 0.000), (b) is in focus at an intermediate distance (β = −0.009), and (c) is in focus. Aberration diagrams at close focus (β = −0.036) are shown. It is sectional drawing which shows the structure of the optical system which concerns on 3rd Example, (a) is at the time of an infinite focus ((beta) = 0.000), (b) is at the time of an intermediate distance focus ((beta) =-0.009), (c ) Shows the arrangement when focusing on a close range (β = −0.036). FIG. 6 is a diagram illustrating various aberrations of the optical system according to Example 3, wherein (a) is in focus at infinity (β = 0.000), (b) is in focus at intermediate distance (β = −0.009), and (c) is in focus. Aberration diagrams at close focus (β = −0.036) are shown. It is a figure explaining the digital camera (optical apparatus) carrying the optical system which concerns on this embodiment, (a) is a front view, (b) is a rear view. It is sectional drawing along the AA 'line of Fig.7 (a). It is a flowchart for demonstrating the manufacturing method of the optical system which concerns on this embodiment.

Hereinafter, embodiments will be described with reference to the drawings. Optical system WL according to this embodiment
1 includes a first lens group G1 having a negative refractive power and a second lens group G2, which are arranged in order from the object side along the optical axis, and the first lens group G1 includes: A first lens L11 having negative refractive power arranged in order from the object side along the optical axis, a second lens L12 having negative refractive power with the object side surface facing the concave surface toward the object side, 3 lens L13, and the following conditional expression (1
) Is satisfied.

-23.0 <νd3−νd2 <24.2 (1)
However,
νd3: Abbe number based on the d-line of the third lens L13,
νd2: Abbe number based on the d-line of the second lens L12.

In general, in designing an imaging optical system such as a photographic lens, it is difficult to increase the angle of view and increase the aperture while maintaining the size of the optical system. As the aperture becomes larger, it becomes more difficult to correct spherical aberration, to achieve both meridional coma and sagittal coma, and to correct both coma and astigmatism. Further, if the angle is widened without enlarging the optical system, it becomes difficult to correct spherical aberration, astigmatism, and various chromatic aberrations. However, the optical system WL according to the present embodiment is small in size and has a large aperture of about Fno 2.0 and an angle of view, while the lens barrel can be retracted into the camera when the camera is not used. Sagittal coma aberration can be reduced without increasing meridional coma aberration while achieving a wide field angle of about 75 °.

Conditional expression (1) indicates that the Abbe number and the third number of the second lens L12 constituting the first lens group G1.
This defines the difference in Abbe number of the lens L13. By satisfying conditional expression (1), axial chromatic aberration and lateral chromatic aberration can be corrected well simultaneously. If the upper limit of conditional expression (1) is exceeded, the Abbe number of the second lens L12 becomes too small with respect to the Abbe number of the third lens L13, so that it is difficult to correct axial chromatic aberration. If the lower limit value of conditional expression (1) is not reached, the Abbe number of the second lens L12 becomes too large with respect to the Abbe number of the third lens L13, making it difficult to correct lateral chromatic aberration.

  In the optical system WL of the present embodiment, it is preferable that the following conditional expression (2) is satisfied.

fL1 / fL2 <0.2 (2)
However,
fL1: the focal length of the first lens L11,
fL2: focal length of the second lens L12.

Conditional expression (2) indicates that the first lens L11 and the second lens L constituting the first lens group G1.
It defines the ratio of 12 focal lengths. By satisfying conditional expression (2), coma can be reduced without increasing distortion and curvature of field. Conditional expression (2)
If the upper limit is exceeded, the refractive power of the second lens L12 becomes too large with respect to the refractive power of the first lens L11. This effectively corrects meridional coma aberration,
Correction of sagittal coma becomes difficult.

  In the optical system WL of the present embodiment, it is preferable that the following conditional expression (3) is satisfied.

2.55 <(-R21) / R12 (3)
However,
R21: radius of curvature of the object side surface of the second lens L12,
R12: radius of curvature of the image side surface of the first lens L11.
The curvature radii R21 and R12 are positive when the convex surface is directed to the object side.

Conditional expression (3) defines the ratio of the curvature radii of the image side surface of the first lens L11 and the object side surface of the second lens L12 constituting the first lens group G1. By satisfying conditional expression (3), sagittal coma can be reduced without increasing meridional coma. If the lower limit of conditional expression (3) is not reached, the absolute value of the radius of curvature of the object side surface of the second lens L12 becomes too large in order to maintain the refractive power of the second lens L12. Thereby, the meridional coma aberration can be corrected effectively, but the sagittal coma aberration becomes difficult to correct.

In the optical system WL of the present embodiment, the third lens L13 constituting the first lens group G1.
Preferably has a positive refractive power. With this configuration, distortion and lateral chromatic aberration can be favorably corrected.

In the optical system WL of the present embodiment, the first lens L11, the second lens L12, and the third lens
The lenses L13 are preferably single lenses. With this configuration, distortion and lateral chromatic aberration can be favorably corrected.

In the optical system WL of the present embodiment, it is preferable that the second lens group G2 has a positive refractive power. With this configuration, the present optical system WL is made compact by adopting a retrofocus type in which a lens group having a positive refractive power is disposed on the image side of the first lens group G1 having a negative refractive power. A wide angle of view can be achieved while suppressing aberrations.

In the optical system WL of the present embodiment, it is preferable to dispose the aperture stop S closer to the object side than the second lens group G2. With this configuration, it is possible to satisfactorily correct distortion and field curvature while reducing the effective diameter of the most object side lens, that is, the first lens L11 (of the first lens group G1). Further, it is possible to reduce the thickness of the lens barrel when the lens barrel is retracted when the camera is not used, and the camera can be reduced in thickness.

In the optical system WL of the present embodiment, it is preferable that at least one surface of the first lens L11 is an aspherical surface. By using an aspherical surface for the first lens L11 through which the off-axis ray passes through a position far from the optical axis, the field curvature and astigmatism are corrected well, and the optical system WL
It is possible to satisfactorily correct aberrations of the entire system. In general, if it is intended to achieve a wide angle of view in an optical system in which the first lens unit G1 closest to the object side has a negative refractive power, the negative refractive power of the first lens unit G1 is increased. Therefore, it becomes difficult to correct the aberration. However, this problem can be solved if at least one surface of the first lens L11 constituting the first lens group G1 is an aspheric surface as in the optical system WL according to the present embodiment. Although it is possible to correct the aberration by increasing the number of lenses constituting the first lens group G1, if the number of lenses in the first lens group G1 increases, the lens when the camera is not used, that is, when the lens is retracted. The thickness of the lens barrel will increase, and miniaturization cannot be achieved.

According to the optical system WL according to the present embodiment as described above, the lens barrel can be retracted into the camera when the camera is not used, but it is small and has a wide angle of view (about 75 °). An optical system having a large aperture (about Fno 2.0) can be realized.

7 and 8, a digital still camera C is shown as an optical apparatus including the above-described optical system WL.
The structure of AM (optical apparatus) is shown. In this digital still camera CAM, when a power button (not shown) is pressed, a shutter (not shown) of a photographing lens (optical system WL) is opened, and light from a subject (object) is condensed by the optical system WL, and an image is displayed. An image sensor C (for example, arranged on the surface I (see FIG. 1))
The image is formed on a CCD or CMOS. The subject image formed on the image sensor C is displayed on the liquid crystal monitor M disposed behind the digital still camera CAM. The photographer determines the composition of the subject image while looking at the liquid crystal monitor M, and then depresses the release button B1 to photograph the subject image with the image sensor C, and records and saves it in a memory (not shown).

The camera CAM is provided with an auxiliary light emitting unit EF for emitting auxiliary light when the subject is dark, a function button B2 used for setting various conditions of the digital still camera CAM, and the like. Here, a compact type camera in which the camera CAM and the optical system WL are integrally formed is illustrated. However, as an optical device, a single-lens reflex camera in which a lens barrel having the optical system WL and a camera body main body are detachable can be used. good.

Next, a method for manufacturing the above-described optical system WL will be described with reference to FIG. First,
In the lens barrel, the first lens group G1 and the second lens group G2 are incorporated in order from the object side along the optical axis (step ST10). At this time, as the first lens group G1, in order from the object side along the optical axis, the first lens L11 having negative refractive power and the first lens group L1 having negative refractive power with the object side surface facing the concave surface toward the object side. A second lens L12 and a third lens L13 are arranged. Further, when the Abbe number based on the d-line of the third lens L13 is νd3 and the Abbe number based on the d-line of the second lens L12 is νd2, the following conditional expression (1) is satisfied. Thus, each lens is incorporated in the lens barrel (step ST20).

  -23.0 <νd3−νd2 <24.2 (1)

Here, as an example of the lens arrangement in the present embodiment, as shown in FIG. 1, as the first lens group G1, the object side surface is negative with the convex surface facing the object side in order from the object side along the optical axis. A meniscus lens L11 (corresponding to the first lens), a negative meniscus lens L12 (corresponding to the second lens) with the object side facing the concave surface on the object side, and a biconvex positive lens L13 (corresponding to the third lens) Applicable) and have negative refractive power as a whole. Second lens group G2
In order from the object side along the optical axis, a biconvex positive lens L21, a cemented lens of a biconvex positive lens L22 and a biconcave negative lens L23, and a biconcave negative lens L24 A cemented lens with a biconvex positive lens L25 is incorporated so as to have a positive refractive power as a whole. As the third lens group G3, a biconvex positive lens L31 is incorporated so as to have a positive refractive power as a whole.

According to the manufacturing method of the optical system according to the present embodiment as described above, the lens barrel can be retracted into the camera when the camera is not used, but it is small and has a wide angle of view (about 75 °). )
Thus, an optical system having a large aperture (about Fno 2.0) can be obtained.

Each example according to the present embodiment will be described with reference to the drawings. Table 1 below
Table 3 is shown, but these are tables of specifications in the first to third examples.

In each embodiment, the C-line (wavelength 656.2730 nm), d-line (wavelength) are calculated as aberration characteristics.
587.5620nm), F line (wavelength 486.1330nm), g line (wavelength 435.8350nm).

In [Lens Specifications] in the table, the surface number is the order of the optical surfaces from the object side along the light traveling direction, R is the radius of curvature of each optical surface, D is the next optical surface from each optical surface ( Or an optical surface distance to the image surface), nd is a refractive index of the material of the optical member with respect to the d-line, and νd is an Abbe number based on the d-line of the material of the optical member. The object surface is the object surface, (variable) is the variable surface interval, “∞” of the radius of curvature is the plane or aperture, (aperture FS) is the flare-cut aperture FS, (aperture S) is the aperture aperture S, The image plane indicates the image plane I. The refractive index of air “1.000000” is omitted. When the optical surface is an aspherical surface, the surface number is marked with *, and the column of curvature radius R indicates the paraxial curvature radius.

In [Aspherical data] in the 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, r is the radius of curvature of the reference sphere (paraxial radius of curvature), and κ is Ai represents the i-th aspherical coefficient. “E-n” indicates “× 10 ⁻ⁿ ”. For example, 1.234E-05 = 1.234 × 10 ⁻⁵ .

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 [various data], β is a photographing magnification at each in-focus position, f is a focal length of the entire optical system, FNO is an F number, ω is a half field angle (maximum incident angle, unit: °), and Y is an image height. , TL is the total length of the optical system, Bf is the distance from the image side surface of the optical member arranged closest to the image side to the paraxial image plane,
Bf (air conversion) indicates the distance when the air conversion from the final optical surface to the paraxial image surface is performed.

In [Variable surface interval data], β indicates a photographing magnification at each in-focus position, and Di indicates a variable surface interval of the i-th surface.

  In [Conditional Expression], values corresponding to the conditional expressions (1) to (3) are shown.

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. Further, the unit is not limited to “mm”, and other appropriate units can be used.

  The description of the table so far is common to all the embodiments, and the description below is omitted.

(First embodiment)
A first embodiment will be described with reference to FIGS. 1 and 2 and Table 1. FIG. As shown in FIG. 1, the optical system WL (WL1) according to the first example includes a first lens group G1 having negative refractive power arranged in order from the object side along the optical axis, and a flare-cut stop FS. And an aperture stop S, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, and a filter group FL.

The first lens group G1 includes a negative meniscus lens L11 having a convex surface facing the object side, a negative meniscus lens L12 having a concave surface facing the object side, and a biconvex positive lens arrayed in order from the object side along the optical axis. Lens L13. An aspherical surface is formed on the image side lens surface of the negative lens L11.

The second lens group G2 is a biconvex positive lens L21 arranged in order from the object side along the optical axis.
And a cemented lens of a biconvex positive lens L22 and a biconcave negative lens L23, and a cemented lens of a biconcave negative lens L24 and a biconvex positive lens L25. Positive lens L2
An aspherical surface is formed on the lens surface 5 on the image side.

  The third lens group G3 is composed of a biconvex positive lens L31.

The filter group FL is a solid-state imaging device (for example, CCD or CMOS) disposed on the image plane I.
It is composed of a low-pass filter, an infrared cut filter, and the like for cutting a spatial frequency above the limit resolution.

In the optical system WL1 according to the first example having such a configuration, the magnification β = − from an object at infinity.
It is desirable that focusing on a finite distance object of about 0.036 is performed by moving the third lens group G3 along the optical axis. It is desirable that focusing on a finite distance object closer than the magnification β = −0.036 is performed by moving the second lens group G2 and the third lens group G3 along the optical axis, respectively.

Table 1 below shows the values of each item in the first example. Surface numbers 1 to 22 in Table 1 correspond to the optical surfaces having the curvature radii R1 to R22 shown in FIG. In the first embodiment, the second surface and the sixteenth surface are aspherical surfaces.

(Table 1)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 3.0675 0.0865 1.5889 61.18
* 2 0.6059 0.4621
3 -1.7942 0.0703 1.6477 33.72
4 -2.6821 0.0054
5 2.8738 0.1270 1.9108 35.25
6 -9.2330 0.2432
7 (Aperture FS) ∞ D7 (Variable)
8 (Aperture S) ∞ 0.0054
9 0.9156 0.2795 1.4978 82.57
10 -2.5496 0.0300
11 1.3142 0.1424 1.8160 46.59
12 -3.3908 0.0540 1.6398 34.55
13 0.9273 0.1943
14 -1.1082 0.1395 1.7408 27.74
15 3.2628 0.1170 1.8513 40.10
* 16 -1.8675 D16 (variable)
17 4.0834 0.1277 1.6180 63.34
18 -6.8503 D18 (variable)
19 ∞ 0.0859 1.5168 64.20
20 ∞ 0.0541
21 ∞ 0.0378 1.5168 64.20
22 ∞ BF
Image plane ∞

[Aspherical data]
2nd surface κ = 0.7323, A4 = -3.7914E-02, A6 = -3.4715E-01, A8 = 7.9334E-01, A10 = -2.7509E + 00
16th surface κ = 1.0000, A4 = 3.9172E-01, A6 = 7.6310E-01, A8 = -6.1183E-02, A10 = 4.3105E + 00

[Various data]
β 0.000 -0.036 -0.179
f 1.000 0.983 1.011
FNO 2.057 2.056 2.219
ω 38.624 22.289 4.452
Y 0.783 0.783 0.783
TL 3.792 3.792 3.762
BF 0.038 0.038 0.038
BF (air conversion) 0.812 0.905 1.090

[Variable surface interval data]
β 0.000 -0.036 -0.179
D7 0.559 0.559 0.413
D16 0.293 0.201 0.162
D18 0.639 0.731 0.916
BF 0.038 0.038 0.038

[Conditional expression]
νd2 = 33.72
νd3 = 35.25
fL1 = -1.3011
fL2 = -8.9628
R12 = 0.6059
R21 = -1.7942
Conditional expression (1) νd3−νd2 = -1.53
Conditional expression (2) fL1 / fL2 = 0.1452
Conditional expression (3) (-R21) / R12 = 2.889

From Table 1, it can be seen that the optical system WL1 according to the first example satisfies the conditional expressions (1) to (3).

FIG. 2 is a diagram showing various aberrations (spherical aberration diagram, astigmatism diagram, distortion diagram, coma aberration diagram and chromatic aberration diagram of magnification) of the optical system WL1 according to the first example, and (a) is infinite focus. Hour (β = 0.000), (
b) shows various aberration diagrams when the intermediate distance is in focus (β = −0.036), and (c) shows the various aberrations when the close focus is in focus (β = −0.179).

In each aberration diagram, FNO is the F number, NA is the numerical aperture, and A is the half angle of view for each image height (
(Unit: °), and H0 represents the object height. d is the d-line, g is the g-line, C is the C-line, and F is the F-line aberration. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the coma aberration diagram, the solid line indicates meridional coma aberration, the dotted line indicates sagittal coma aberration, the dotted line on the right side from the origin indicates the sagittal coma aberration generated in the meridional direction with respect to the d line, and the dotted line on the left side from the origin indicates the sagittal direction with respect to the d line. Shows the sagittal coma aberration that occurs in each. In the aberration diagrams of each example described later, the same symbols as those in this example are used.

As is apparent from the aberration diagrams shown in FIGS. 2A to 2C, the optical system WL according to the first example.
It can be seen that No. 1 has excellent imaging performance with various aberrations corrected satisfactorily.

(Second embodiment)
The second embodiment will be described with reference to FIGS. 3 and 4 and Table 2. FIG. As shown in FIG. 3, the optical system WL (WL2) according to the second example includes a first lens group G1 having negative refractive power arranged in order from the object side along the optical axis, and a flare-cut stop FS. And an aperture stop S, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, and a filter group FL.

The first lens group G1 includes a negative meniscus lens L11 having a convex surface facing the object side, a negative meniscus lens L12 having a concave surface facing the object side, and a biconvex positive lens arrayed in order from the object side along the optical axis. Lens L13. An aspherical surface is formed on the image side lens surface of the negative lens L11.

The second lens group G2 is a biconvex positive lens L21 arranged in order from the object side along the optical axis.
And a cemented lens of a biconvex positive lens L22 and a biconcave negative lens L23, and a cemented lens of a biconcave negative lens L24 and a biconvex positive lens L25. Positive lens L2
An aspherical surface is formed on the lens surface 5 on the image side.

  The third lens group G3 is composed of a biconvex positive lens L31.

The filter group FL is a solid-state imaging device (for example, CCD or CMOS) disposed on the image plane I.
It is composed of a low-pass filter, an infrared cut filter, and the like for cutting a spatial frequency above the limit resolution.

In the optical system WL2 according to the second example having such a configuration, the magnification β = − from an object at infinity.
It is desirable that focusing on a finite distance object of about 0.036 is performed by moving the third lens group G3 along the optical axis. It is desirable that focusing on a finite distance object closer than the magnification β = −0.036 is performed by moving the second lens group G2 and the third lens group G3 along the optical axis, respectively.

Table 2 below shows the values of each item in the second embodiment. Surface numbers 1 to 22 in Table 2 correspond to the optical surfaces having the curvature radii R1 to R22 shown in FIG. In the second embodiment, the second surface and the sixteenth surface are aspherical surfaces.

(Table 2)
[Lens specifications]
Surface number R D nd νd
Object ∞
1 2.1637 0.0865 1.6516 58.57
* 2 0.6042 0.4694
3 -1.7507 0.0703 1.6700 57.35
4 -2.5109 0.0054
5 2.4999 0.1198 1.9108 35.25
6 -52.2956 0.2432
7 (Aperture FS) ∞ D7 (Variable)
8 (Aperture S) ∞ 0.0054
9 0.9370 0.2274 1.4978 82.57
10 -2.6585 0.0300
11 1.2910 0.1576 1.8160 46.59
12 -2.8071 0.0541 1.6398 34.55
13 0.9366 0.2032
14 -1.1194 0.1622 1.7408 27.74
15 3.0615 0.1191 1.8513 40.10
* 16 -1.9609 D16 (variable)
17 3.3931 0.1295 1.6180 63.34
18 -9.4947 D18 (variable)
19 ∞ 0.0859 1.5168 64.20
20 ∞ 0.0541
21 ∞ 0.0378 1.5168 64.20
22 ∞ BF
Image plane ∞

[Aspherical data]
2nd surface κ = 0.7466, A4 = -2.9535E-02, A6 = -3.0881E-01, A8 = 7.8703E-01, A10 = -2.6992E + 00
16th surface κ = 1.0000, A4 = 3.8500E-01, A6 = 6.8014E-01, A8 = 1.3926E-01, A10 = 2.9104E + 00

[Various data]
β 0.000 -0.009 -0.036
f 1.000 0.996 0.984
FNO 2.051 0.002 0.009
ω 38.624 87.096 22.281
Y 0.783 0.783 0.783
TL 3.820 3.820 3.820
BF 0.378 0.378 0.378
BF (air equivalent) 1.189 1.212 1.276

[Variable surface interval data]
β 0.000 -0.009 -0.036
D7 0.569 0.569 0.569
D16 0.277 0.254 0.190
D18 0.675 0.698 0.762
BF 0.378 0.378 0.378

[Conditional expression]
νd2 = 57.35
νd3 = 35.25
fL1 = -1.3152
fL2 = -8.9629
R12 = 0.6042
R21 = -1.7507
Conditional expression (1) νd3−νd2 = -22.10.
Conditional expression (2) fL1 / fL2 = 0.1467
Conditional expression (3) (-R21) /R12=2.898

From Table 2, it can be seen that the optical system WL2 according to the second example satisfies the conditional expressions (1) to (3).

FIG. 4 is a diagram showing various aberrations (spherical aberration diagram, astigmatism diagram, distortion diagram, coma aberration diagram and chromatic aberration diagram of magnification) of the optical system WL2 according to the second example, and (a) is infinite focus. Hour (β = 0.000), (
b) shows various aberration diagrams when focusing at an intermediate distance (β = −0.009), and (c) shows various aberrations when focusing at a close distance (β = −0.036).

As is apparent from the respective aberration diagrams shown in FIGS. 4A to 4C, the optical system WL according to the second example.
No. 2 shows that various aberrations are corrected favorably and has excellent imaging performance.

(Third embodiment)
A third embodiment will be described with reference to FIGS. 5 and 6 and Table 3. FIG. As shown in FIG. 5, the optical system WL (WL3) according to the third example includes a first lens group G1 having negative refractive power arranged in order from the object side along the optical axis, and a flare-cut stop FS. And an aperture stop S, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, and a filter group FL.

The first lens group G1 is arranged in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface facing the object side, a negative meniscus lens L12 having a concave surface facing the object side, and a convex surface facing the object side. And a positive meniscus lens L13. Aspheric surfaces are formed on the object-side and image-side lens surfaces of the negative lens L11.

The second lens group G2 is a biconvex positive lens L21 arranged in order from the object side along the optical axis.
And a cemented lens of a biconvex positive lens L22 and a biconcave negative lens L23, and a cemented lens of a biconcave negative lens L24 and a biconvex positive lens L25. Positive lens L2
An aspherical surface is formed on the lens surface 5 on the image side.

  The third lens group G3 is composed of a biconvex positive lens L31.

The filter group FL is a solid-state imaging device (for example, CCD or CMOS) disposed on the image plane I.
It is composed of a low-pass filter, an infrared cut filter, and the like for cutting a spatial frequency above the limit resolution.

In the optical system WL3 according to the third example having such a configuration, the magnification β = − from an object at infinity.
It is desirable that focusing on a finite distance object of about 0.036 is performed by moving the third lens group G3 along the optical axis. It is desirable that focusing on a finite distance object closer than the magnification β = −0.036 is performed by moving the second lens group G2 and the third lens group G3 along the optical axis, respectively.

Table 3 below shows values of various specifications in the third example. Surface numbers 1 to 22 in Table 3 correspond to the optical surfaces having the curvature radii R1 to R22 shown in FIG. In the third embodiment, the first surface, the second surface, and the sixteenth surface are aspherical surfaces.

(Table 3)
[Lens specifications]
Surface number R D nd νd
Object ∞
* 1 2.7352 0.0865 1.5691 71.31
* 2 0.5942 0.4818
3 -1.5351 0.0703 1.9459 17.98
4 -1.6290 0.0054
5 2.0037 0.1074 1.7995 42.09
6 6.5923 0.2432
7 (Aperture FS) ∞ D7 (Variable)
8 (Aperture S) ∞ 0.5475
9 0.9412 0.2465 1.4978 82.57
10 -3.0012 0.0300
11 1.2540 0.1514 1.8160 46.59
12 -3.3541 0.0541 1.6259 35.72
13 0.9427 0.2405
14 -1.1378 0.1110 1.7408 27.74
15 1.9537 0.1395 1.8513 40.10
* 16 -1.8564 D16 (variable)
17 3.3216 0.1464 1.6180 63.34
18 -27.8378 D18 (variable)
19 ∞ 0.0859 1.5168 64.20
20 ∞ 0.0541
21 ∞ 0.0378 1.5168 64.20
22 ∞ BF
Image plane ∞

[Aspherical data]
1st surface κ = 1.0000, A4 = -4.5412E-02, A6 = 2.5782E-02, A8 = 0.0000E + 00, A10 = 0.0000E + 00
2nd surface κ = 0.7000, A4 = -6.7660E-02, A6 = -3.9725E-01, A8 = 6.4185E-01, A10 = -2.2663E + 00
16th surface κ = 1.0000, A4 = 4.0710E-01, A6 = 8.1699E-01, A8 = -3.5427E-01, A10 = 3.6897E + 00

[Various data]
β 0.000 -0.009 -0.036
f 1.000 0.995 0.981
FNO 2.051 0.002 0.009
ω 38.624 87.094 22.278
Y 0.783 0.783 0.783
TL 3.768 3.768 3.768
BF 0.038 0.038 0.038
BF (air equivalent) 0.702 0.732 0.815

[Variable surface interval data]
β 0.000 -0.009 -0.036
D7 0.548 0.548 0.548
D16 0.357 0.327 0.245
D18 0.529 0.559 0.641
BF 0.378 0.378 0.378

[Conditional expression]
νd2 = 17.98
νd3 = 42.09
fL1 = -1.3536
fL2 = -44.2169
R12 = 0.5942
R21 = -1.5351
Conditional expression (1) νd3−νd2 = 24.110
Conditional expression (2) fL1 / fL2 = 0.0306
Conditional expression (3) (-R21) / R12 = 2.584

From Table 3, it can be seen that the optical system WL3 according to the third example satisfies the conditional expressions (1) to (3).

FIG. 6 is a diagram showing various aberrations (spherical aberration diagram, astigmatism diagram, distortion diagram, coma diagram, and chromatic aberration diagram of magnification) of the optical system WL3 according to the third example, and (a) is infinite focus. Hour (β = 0.000), (
b) shows various aberration diagrams when focusing at an intermediate distance (β = −0.009), and (c) shows various aberrations when focusing at a close distance (β = −0.036).

As is apparent from the aberration diagrams shown in FIGS. 6A to 6C, the optical system WL according to the third example.
No. 3 shows that various aberrations are corrected well and has excellent imaging performance.

In order to make the present invention easier to understand, the configuration requirements of the embodiment have been described, but it goes without saying that the present invention is not limited to this.

WL (WL1 to WL3) optical system G1 first lens group G2 second lens group G3 third lens group L11 (which constitutes the first lens group) first lens L12 (which constitutes the first lens group) second Lens L13 Third lens (constituting the first lens group) FS Flare cut stop S Aperture stop FL Filter group I Image plane CAM Digital still camera (optical equipment)

Claims (8)

The first lens group having negative refractive power, the aperture stop, the second lens group, and the third lens group having positive refractive power, which are arranged in order from the object side along the optical axis, are substantially 3 Consisting of a group of lenses
The first lens group includes a first lens having negative refractive power arranged in order from the object side along the optical axis, and a second lens having negative refractive power with the object side surface facing the concave surface toward the object side. A lens and a third lens;
The third lens group includes a single lens having a positive refractive power,
An optical system satisfying the following conditional expression:
−23.0 <νd3−νd2 <24.2
fL1 / fL2 <0.2
However,
νd3: Abbe number based on the d-line of the third lens,
νd2: Abbe number based on the d-line of the second lens,
fL1: the focal length of the first lens,
fL2: focal length of the second lens. The optical system according to claim 1 , wherein the following conditional expression is satisfied.
2.55 <(-R21) / R12
However,
R21: radius of curvature of the object side surface of the second lens,
R12: radius of curvature of the image side surface of the first lens.
The curvature radii R21 and R12 are positive when the convex surface is directed to the object side. The optical system according to claim 1 , wherein the third lens has a positive refractive power. Said first lens, said second lens and said third lens is an optical system according to claim 1, characterized in that both a single lens. The optical system according to claim 1 , wherein the second lens group has a positive refractive power. The optical system according to claim 1, wherein at least one surface of the first lens is an aspherical surface. An optical apparatus comprising the optical system according to any one of claims 1 to 6 . The first lens group having negative refractive power, the aperture stop, the second lens group, and the third lens group having positive refractive power, which are arranged in order from the object side along the optical axis, are substantially 3 A method for producing an optical system comprising a plurality of lens groups,
The first lens group includes a first lens having negative refractive power arranged in order from the object side along the optical axis, and a second lens having negative refractive power with the object side surface facing the concave surface toward the object side. A lens and a third lens;
The third lens group includes a single lens having a positive refractive power,
A method of manufacturing an optical system, wherein each lens is incorporated in a lens barrel so as to satisfy the following conditional expression:
−23.0 <νd3−νd2 <24.2
fL1 / fL2 <0.2
However,
νd3: Abbe number based on the d-line of the third lens,
νd2: Abbe number based on the d-line of the second lens,
fL1: the focal length of the first lens,
fL2: focal length of the second lens.

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