JP2023060139A - Optical system, optical device, and method of manufacturing optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system that is well corrected for various aberrations.

SOLUTION: An optical system LS provided herein comprises an aperture stop S and a negative lens (L32) located on the image side of the aperture stop S and configured to satisfy the following conditional expressions: ndN2+(0.01425×νdN2)<2.12, 18.0<νdN2<35.0, 0.702<θgFN2+(0.00316×νdN2), where ndN2 represents a refractive index of the negative lens for the d-ray, νdN2 represents an Abbe number of the negative lens for the d-ray, and θgFN2 represents a partial dispersion ratio of the negative lens, defined as: θgFN2=(ngN2-nFN2)/(nFN2-nCN2), where ngN2 represents a refractive index of the negative lens for the g-ray, nFN2 represents a refractive index of the negative lens for the F-ray, and nCN2 represents a refractive index of the negative lens for the C-ray.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention relates to optical systems, optical instruments, and methods of manufacturing optical systems.

2. Description of the Related Art In recent years, image pickup elements used in image pickup apparatuses such as digital cameras and video cameras have increasingly high pixel counts. In addition to standard aberrations (single-wavelength aberrations) such as spherical aberration and coma, the photographic lens provided in an imaging device using such an image sensor also has good chromatic aberration so that the color of the image does not blur under a white light source. It is desired that the lens has a high resolving power and is corrected to . In particular, in the correction of chromatic aberration, it is desirable that the secondary spectrum be well corrected in addition to the primary achromatization. As means for correcting chromatic aberration, for example, a method using a resin material having anomalous dispersion is known (see, for example, Patent Document 1). As described above, with the recent increase in the number of pixels of an image sensor, there is a demand for a photographing lens in which various aberrations are well corrected.

JP 2016-194609 A

An optical system according to a first aspect has an aperture stop and a negative lens that satisfies the following conditional expression and is arranged on the image side of the aperture stop.
ndN2+(0.01425×νdN2)<2.12
18.0<νdN2<35.0
0.702<θgFN2+(0.00316×νdN2)
where ndN2: the refractive index of the negative lens for the d-line; νdN2: the Abbe's number of the negative lens with respect to the d-line; θgFN2=(ngN2−nFN2)/(nFN2−nCN2) where nFN2 is the refractive index of the negative lens for the F line and nCN2 is the refractive index of the negative lens for the C line.

An optical instrument according to a second aspect includes the optical system described above.

In the method of manufacturing an optical system according to the third aspect, each lens is arranged in a lens barrel so as to have an aperture stop and a negative lens that is arranged closer to the image side than the aperture stop and satisfies the following conditional expression: Deploy.
ndN2+(0.01425×νdN2)<2.12
18.0<νdN2<35.0
0.702<θgFN2+(0.00316×νdN2)
where ndN2: the refractive index of the negative lens for the d-line; νdN2: the Abbe's number of the negative lens with respect to the d-line; θgFN2=(ngN2−nFN2)/(nFN2−nCN2) where nFN2 is the refractive index of the negative lens for the F line and nCN2 is the refractive index of the negative lens for the C line.

FIG. 2 is a lens configuration diagram of the optical system according to the first example in an infinity focused state; 4A and 4B are various aberration diagrams in the infinity focused state of the optical system according to the first example. FIG. 10 is a lens configuration diagram of the optical system according to the second example in an infinity focused state; It is an aberration diagram in the infinity focus state of the optical system which concerns on 2nd Example. FIG. 11 is a lens configuration diagram of the optical system according to the third embodiment in an infinity focused state; 6(A), 6(B), and 6(C) respectively show the wide-angle end state, intermediate focal length state, and telephoto end state of the optical system according to the third embodiment when focusing on infinity. It is an aberration diagram. FIG. 11 is a lens configuration diagram of the optical system according to the fourth example in an infinity focused state; 8(A), 8(B), and 8(C) respectively show the wide-angle end state, the intermediate focal length state, and the telephoto end state of the optical system according to the fourth embodiment when focusing on infinity. It is an aberration diagram. FIG. 11 is a lens configuration diagram of the optical system according to the fifth embodiment in an infinity focused state; FIG. 11 is a diagram of various aberrations in the infinity focused state of the optical system according to Example 5; It is a figure showing composition of a camera provided with an optical system concerning this embodiment. It is a flow chart which shows the manufacturing method of the optical system concerning this embodiment.

An optical system and an optical apparatus according to this embodiment will be described below with reference to the drawings. First, a camera (optical device) having an optical system according to this embodiment will be described with reference to FIG. This camera 1 is a digital camera provided with an optical system according to this embodiment as a photographing lens 2 as shown in FIG. In the camera 1 , light from an object (subject) (not shown) is condensed by the photographing lens 2 and reaches the imaging device 3 . As a result, the light from the subject is imaged by the imaging element 3 and recorded in a memory (not shown) as an image of the subject. In this manner, the photographer can photograph the subject with the camera 1. FIG. This camera may be a mirrorless camera or a single-lens reflex type camera having a quick return mirror.

As shown in FIG. 1, an optical system LS (1) as an example of an optical system (taking lens) LS according to the present embodiment includes an aperture stop S and the following conditional expression and a negative lens (L32) that satisfies (1) to (3).

ndN2+(0.01425×νdN2)<2.12 (1)
18.0<νdN2<35.0 (2)
0.702<θgFN2+(0.00316×νdN2) (3)
where ndN2: refractive index of the negative lens for the d-line νdN2: Abbe number of the negative lens with respect to the d-line θgFN2: partial dispersion ratio of the negative lens, where ngN2 is the refractive index of the negative lens for the g-line, and θgFN2=(ngN2−nFN2)/(nFN2−nCN2) where nFN2 is the refractive index for the F line and nCN2 is the refractive index for the C line of the negative lens.
The Abbe number νdN2 of the negative lens with respect to the d-line is defined by the following equation: νdN2=(ndN2−1)/(nFN2−nCN2)

According to this embodiment, in the correction of chromatic aberration, it is possible to obtain an optical system in which the secondary spectrum is well corrected in addition to the primary achromatization, and an optical apparatus equipped with this optical system. The optical system LS according to this embodiment may be the optical system LS(2) shown in FIG. 3, the optical system LS(3) shown in FIG. 5, or the optical system LS(4) shown in FIG. The optical system LS(5) shown in 9 may also be used.

Conditional expression (1) defines an appropriate relationship between the refractive index of the negative lens for the d-line and the Abbe number based on the d-line. By satisfying the conditional expression (1), it is possible to satisfactorily correct the reference aberration such as spherical aberration and coma, and correct (achromatic) the first-order chromatic aberration.

If the corresponding value of conditional expression (1) exceeds the upper limit, for example, the Petzval sum becomes small, which makes it difficult to correct curvature of field, which is not preferable. By setting the upper limit of conditional expression (1) to 2.11, the effects of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, it is preferable to set the upper limit of conditional expression (1) to 2.10, 2.09, 2.08, 2.07, and further 2.06.

Conditional expression (2) defines an appropriate range of the Abbe's number based on the d-line of the negative lens. By satisfying the conditional expression (2), it is possible to satisfactorily correct the reference aberration such as spherical aberration and coma, and correct the first-order chromatic aberration (achromatization).

If the corresponding value of conditional expression (2) exceeds the upper limit, for example, it becomes difficult to correct axial chromatic aberration in the subgroup on the image side of the aperture stop S, which is not preferable. By setting the upper limit of conditional expression (2) to 32.5, the effect of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, the upper limit of conditional expression (2) is set to 32.0, 31.5, 31.0, 30.5, 30.0, and 29.5. is preferred.

If the corresponding value of conditional expression (2) is less than the lower limit, for example, it becomes difficult to correct longitudinal chromatic aberration in the subgroup on the image side of the aperture stop S, which is not preferable. By setting the lower limit of conditional expression (2) to 20.0, the effect of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, the lower limit of conditional expression (2) is set to 23.0, 23.5, 24.0, 24.5, 25.0, 25.5, 26.0. , 26.5, 27.0, 27.5, and preferably 27.7.

Conditional expression (3) appropriately defines the anomalous dispersion of the negative lens. By satisfying the conditional expression (3), in the correction of chromatic aberration, in addition to the primary achromatization, the secondary spectrum can be favorably corrected.

If the corresponding value of conditional expression (3) is below the lower limit, the anomalous dispersion of the negative lens becomes small, making it difficult to correct chromatic aberration. By setting the lower limit of conditional expression (3) to 0.704, the effect of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, it is preferable to set the lower limit of conditional expression (3) to 0.708, 0.710, 0.712, and more preferably 0.715.

In the optical system of this embodiment, the negative lens preferably satisfies the following conditional expression (4).
1.83<ndN2+(0.00787×νdN2) (4)

Conditional expression (4) defines an appropriate relationship between the refractive index of the negative lens for the d-line and the Abbe number based on the d-line. By satisfying the conditional expression (4), it is possible to satisfactorily correct the reference aberration such as spherical aberration and coma, and correct the first-order chromatic aberration (achromatization).

If the corresponding value of conditional expression (4) is less than the lower limit, for example, the refractive index of the negative lens becomes small, which makes it difficult to correct the reference aberration, especially spherical aberration, which is not preferable. By setting the lower limit of conditional expression (4) to 1.84, the effect of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, it is preferable to set the lower limit of conditional expression (4) to 1.85, more preferably 1.86.

In the optical system of this embodiment, the negative lens may satisfy the following conditional expressions (2-1) and (4-1).
18.0<νdN2<26.5 (2-1)
1.83<ndN2+(0.00787×νdN2) (4-1)

Conditional expression (2-1) is similar to conditional expression (2), and can obtain the same effect as conditional expression (2). By setting the upper limit of conditional expression (2-1) to 26.0, the effect of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, it is preferable to set the upper limit of conditional expression (2-1) to 25.5, more preferably 25.0. On the other hand, by setting the lower limit of conditional expression (2-1) to 23.5, the effects of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, it is preferable to set the lower limit of conditional expression (2-1) to 24.0, more preferably 24.5.

Conditional expression (4-1) is similar to conditional expression (4), and can provide the same effect as conditional expression (4). By setting the lower limit of conditional expression (4-1) to 1.90, the effects of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, it is preferable to set the lower limit of conditional expression (4-1) to 1.92, more preferably 1.94.

In the optical system of this embodiment, the negative lens may satisfy the following conditional expressions (2-2) and (4-2).
25.0<νdN2<35.0 (2-2)
1.83<ndN2+(0.00787×νdN2) (4-2)

Conditional expression (2-2) is similar to conditional expression (2), and can obtain the same effect as conditional expression (2). By setting the upper limit of conditional expression (2-2) to 32.5, the effects of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, it is preferable to set the upper limit of conditional expression (2-2) to 31.5, more preferably 29.5. On the other hand, by setting the lower limit of conditional expression (2-2) to 26.2, the effects of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, it is preferable to set the lower limit of conditional expression (2-2) to 26.7, more preferably 27.7.

Conditional expression (4-2) is similar to conditional expression (4), and can obtain the same effect as conditional expression (4). By setting the lower limit of conditional expression (4-2) to 1.84, the effects of the present embodiment can be made more reliable. In order to further ensure the effect of this embodiment, it is preferable to set the lower limit of conditional expression (4-2) to 1.85.

In the optical system of this embodiment, the negative lens preferably satisfies the following conditional expression (5).
DN2>0.80 (5)
However, DN2: the thickness of the negative lens on the optical axis [mm]

Conditional expression (5) defines an appropriate range for the thickness of the negative lens on the optical axis. By satisfying the conditional expression (5), various aberrations such as coma and chromatic aberration (axial chromatic aberration and chromatic aberration of magnification) can be satisfactorily corrected.

If the corresponding value of conditional expression (5) is less than the lower limit, it becomes difficult to correct various aberrations such as coma and chromatic aberration (axial chromatic aberration and chromatic aberration of magnification), which is not preferable. By setting the lower limit of conditional expression (5) to 0.90, the effect of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, the lower limit of conditional expression (5) is set to 1.00, 1.00.
10, 1.20 and even 1.30 are preferred.

The optical system of this embodiment has an image side lens arranged closest to the image side, an aperture stop S is arranged closer to the object side than the image side lens, and the negative lens is the aperture stop S It is desirable to be arranged closer to the image side. This makes it possible to satisfactorily correct various aberrations such as coma and chromatic aberration (axial chromatic aberration and chromatic aberration of magnification).

In the optical system of this embodiment, the negative lens is preferably a glass lens. As a result, it is possible to obtain a lens that is resistant to aging and to environmental changes such as temperature changes, as compared with the case where the material is resin.

In the optical system of this embodiment, the negative lens desirably satisfies the following conditional expressions (6) to (7).
ndN2<1.63 (6)
ndN2−(0.040×νdN2−2.470)×νdN2<39.809 (7)

Conditional expression (6) defines an appropriate range of the refractive index for the d-line of the negative lens. By satisfying the conditional expression (6), various aberrations such as coma and chromatic aberration (axial chromatic aberration and chromatic aberration of magnification) can be satisfactorily corrected.

If the corresponding value of conditional expression (6) exceeds the upper limit, it becomes difficult to correct various aberrations such as coma and chromatic aberration (axial chromatic aberration and chromatic aberration of magnification), which is not preferable. By setting the upper limit of conditional expression (6) to 1.62, the effect of this embodiment can be made more reliable.

Conditional expression (7) defines an appropriate relationship between the refractive index of the negative lens for the d-line and the Abbe number based on the d-line. By satisfying the conditional expression (7), it is possible to satisfactorily correct the reference aberration such as spherical aberration and coma, and correct the first-order chromatic aberration (achromatization).

If the corresponding value of conditional expression (7) exceeds the upper limit, for example, the Petzval sum becomes small, which makes it difficult to correct curvature of field, which is not preferable. By setting the upper limit of conditional expression (7) to 39.800, the effect of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, the upper limit of conditional expression (7) is set to 39.500, 39.000, 38.500, 38.000, 37.500, and further 36.800. is preferred.

In the optical system of this embodiment, the negative lens preferably satisfies the following conditional expression (8).
ndN2−(0.020×νdN2−1.080)×νdN2<16.260 (8)

Conditional expression (8) defines an appropriate relationship between the refractive index of the negative lens for the d-line and the Abbe number based on the d-line. By satisfying the conditional expression (8), it is possible to satisfactorily correct the reference aberration such as spherical aberration and coma, and correct the first-order chromatic aberration (achromatization).

If the corresponding value of conditional expression (8) exceeds the upper limit, for example, the Petzval sum becomes small, making it difficult to correct curvature of field, which is not preferable. By setting the upper limit of conditional expression (8) to 16.240, the effect of this embodiment can be made more reliable. In order to further ensure the effect of this embodiment, the upper limit of conditional expression (8) is set to 16.000, 15.800, 15.500, 15.300, 15.000, 14.800, 14.500 , 14
. 000, preferably 13.500.

Next, referring to FIG. 12, a method for manufacturing the above-described optical system LS will be outlined. First, an aperture stop S and at least a negative lens on the image side of the aperture stop S are arranged (step ST1). At this time, each lens is arranged in the lens barrel so that at least one of the negative lenses arranged on the image side of the aperture stop S satisfies the above conditional expressions (1) to (3) (step ST2). According to such a manufacturing method, in the correction of chromatic aberration, it is possible to manufacture an optical system in which the secondary spectrum is well corrected in addition to the primary achromatization.

An optical system LS according to an example of the present embodiment will be described below with reference to the drawings. 1, 3, 5, 7, and 9 are sectional views showing the configuration and refractive power distribution of the optical system LS {LS(1) to LS(5)} according to the first to fifth embodiments. be. In the cross-sectional views of the optical systems LS(1) and LS(2) according to the first and second examples and the optical system LS(5) according to the fifth example, the focusing lens group is aligned with an object at infinity to a short distance. The direction of movement for focusing is indicated by an arrow together with the word "focus". In the cross-sectional views of the optical systems LS(3) and LS(4) according to the third and fourth examples, the optical axis of each lens group when zooming from the wide-angle end state (W) to the telephoto end state (T) The direction of movement along is indicated by an arrow.

1, 3, 5, 7 and 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 complication due to a large number of types and numbers of symbols and numerals, the lens groups and the like are represented independently using combinations of symbols and numerals for each embodiment. Therefore, even if the same reference numerals and symbols are used between the embodiments, it does not mean that they have the same configuration.

Tables 1 to 5 are shown below, of which Table 1 is the first embodiment, Table 2 is the second embodiment, Table 3 is the third embodiment, Table 4 is the fourth embodiment, and Table 5 is the third embodiment. It is a table|surface which shows each specification data in 5 Example. In each embodiment, aberration characteristics are calculated for d-line (wavelength λ=587.6 nm), g-line (wavelength λ=435.8 nm), C-line (wavelength λ=656.3 nm), F-line (wavelength λ= 486.1 nm) is selected.

In the [Overall specifications] table, f is the focal length of the entire lens system, FNO is the F number, 2ω is the angle of view (unit is ° (degrees), ω is the half angle of view), and Y is the image height. show. TL indicates the distance obtained by adding BF to the distance from the foremost lens surface to the last lens surface on the optical axis when focusing on infinity, and BF is the distance from the last lens surface on the optical axis when focusing on infinity. The distance to plane I (back focus) is shown. If the optical system is a variable power optical system, these values are shown for each variable power state of the wide-angle end (W), the intermediate focal length (M), and the telephoto end (T).

In the [Lens Specifications] table, the surface number indicates the order of the optical surfaces from the object side along the direction in which light rays travel, and R is the radius of curvature of each optical surface (the surface whose center of curvature is located on the image side). is a positive value), D is the distance on the optical axis from each optical surface to the next optical surface (or image plane), nd is the refractive index for the d-line of the material of the optical member, and νd is the optical θgF indicates the Abbe number of the material of the member with reference to the d-line, and θgF indicates the partial dispersion ratio of the material of the optical member. The radius of curvature “∞” indicates a plane or an aperture, and (diaphragm S) indicates an aperture diaphragm S, respectively. The description of the refractive index of air nd=1.00000 is omitted. If the optical surface is an aspherical surface, the surface number is marked with *a. If the optical surface is a diffractive optical surface, the surface number is marked with *b. It shows the radius of curvature of the shaft.

Let ng be the refractive index of the material of the optical member for the g-line (wavelength λ = 435.8 nm), let nF be the refractive index of the material of the optical member for the F-line (wavelength λ = 486.1 nm), and let C be the material of the optical member. Let nC be the refractive index for a ray (wavelength λ=656.3 nm). At this time, the partial dispersion ratio θgF of the material of the optical member is defined by the following equation (A).

θgF=(ng−nF)/(nF−nC) (A)

In the table of [aspheric surface data], the shape of the aspheric surface shown in [lens specifications] is shown by the following equation (B). X(y) is the distance (zag amount) along the optical axis from the tangent plane at the vertex of the aspherical surface to the position on the aspherical surface at height y, and R is the radius of curvature of the reference sphere (paraxial radius of curvature) , κ is the conic constant, and Ai is the i-th order aspheric coefficient. “E-n” indicates “×10 ⁻ⁿ ”. For example, 1.234E-05 = 1.234 x ^10-5 . Note that the second-order aspheric coefficient A2 is 0, and its description is omitted.

X(y)=( ^y2 /R)/{1+(1-κ× ^y2 / ^R2 ) ^1/2 }+A4× ^y4 +A6× ^y6 +A8× ^y8 +A10× ^y10 (B)

When the optical system has a diffractive optical element, the phase shape ψ of the diffractive optical surface shown in [diffractive optical surface data] is expressed by the following equation (C).

ψ(h, m)={2π/(m×λ0)}×(C2× ^h2 +C4× ^h4 +C6× ^h6 ...)...(
C)
however,
h: height in the direction perpendicular to the optical axis;
m: diffraction order of diffracted light,
λ0: design wavelength,
Ci: phase coefficients (i=2, 4, . . . ).

The refractive power φD of the diffractive surface at an arbitrary wavelength λ and an arbitrary diffraction order m can be expressed by the following equation (D) using the phase coefficient C2 of the lowest order.

φD(h,m)=-2×C2×m×λ/λ0 (D)

In the table of [diffractive optical surface data], for the diffractive optical surface shown in [lens specifications], the design wavelength λ0, the diffraction order m, the second-order phase coefficient C2, the fourth-order phase coefficient C4 in the formula (C) indicates
“E-n” indicates “×10 ⁻ⁿ ” as in the [Aspheric data] table.

If the optical system is not a variable-magnification optical system, f indicates the focal length of the entire lens system and β indicates the photographing magnification as [variable interval data for short-distance photographing]. In addition, the [Variable distance data for close-range shooting] table shows the surface distances of the surface numbers for which the surface distance is "variable" in [Lens specifications], corresponding to each focal length and shooting magnification. .

[ [Lens specifications] shows the surface distance for the surface number where the surface distance is "variable". The [lens group data] table shows the starting surface (surface closest to the object side) and focal length of each lens group.

The [value corresponding to conditional expression] table shows the value corresponding to each conditional expression.

Unless otherwise specified, "mm" is generally used for the focal length f, radius of curvature R, surface spacing D, and other lengths in all specifications below, but the optical system is proportionally enlarged. Alternatively, it is not limited to this because equivalent optical performance can be obtained even if it is proportionally reduced.

The description of the table up to this point is common to all the embodiments, and redundant description will be omitted below.

(First embodiment)
A first embodiment will be described with reference to FIGS. 1 and 2 and Table 1. FIG. FIG. 1 is a diagram showing the lens configuration of the optical system according to Example 1 of the present embodiment in an infinity focused state. The optical system LS(1) according to the first example includes, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a positive refractive power. and a third lens group G3 having power. When focusing from an infinity object to a short distance (finite distance) object, the second lens group G2 and the third lens group G3 move by different amounts of movement toward the object side along the optical axis. An aperture stop S is disposed between the second lens group G2 and the third lens group G3, and moves along the optical axis together with the third lens group G3 during focusing. The sign (+) or (-) attached to each lens group symbol indicates the refractive power of each lens group, and this is the same for all the following examples.

The first lens group G1 is a cemented lens composed of a positive meniscus lens L11 having a convex surface facing the object side and a negative meniscus lens L12 having a convex surface facing the object side, arranged in order from the object side, and a cemented lens having a concave surface facing the object side. It is composed of a cemented lens composed of a positive meniscus lens L13 and a biconcave negative lens L14, and a biconvex positive lens L15.

The second lens group G2 is composed of, in order from the object side, a biconvex positive lens L21 and a cemented lens composed of a biconvex positive lens L22 and a biconcave negative lens L23.

The third lens group G3 is a cemented lens composed of a positive meniscus lens L31 with a concave surface facing the object side and a biconcave negative lens L32 arranged in order from the object side, a biconvex positive lens L33 and a biconcave lens. and a biconvex positive lens L35. An image plane I is arranged on the image side of the third lens group G3. In this embodiment, the positive lens L35 of the third lens group G3 corresponds to the image side lens, and the negative lens L32 of the third lens group G3 corresponds to the negative lens that satisfies the conditional expressions (1) to (3). . The positive lens L35 has an aspheric lens surface on the image side.

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

(Table 1)
[Overall specifications]
f48.500
FNO 1.419
2ω 48.286
Y 21.63
TL 142.000
BF 38.800
[Lens specifications]
Surface number R D nd νd θgF
1 54.34110 7.000 2.00100 29.13 0.599
2 117.24740 2.500 1.54814 45.78 0.569
3 27.06680 13.200
4 -55.51090 6.000 1.49700 81.61 0.539
5 -28.83210 2.000 1.61266 44.46 0.564
6 96.35070 2.747
7 89.09580 7.500 1.72916 54.61 0.544
8 -58.51470 D8 (Variable)
9 139.79460 5.000 2.00100 29.13 0.599
10 -162.67090 0.100
11 76.23360 7.500 1.49700 81.61 0.539
12 -50.22910 1.800 1.64769 33.72 0.593
13 99.85150 D13
14 ∞ 4.463 (Aperture S)
15 -67.43970 4.000 1.49782 82.57 0.539
16 -44.95420 1.600 1.65940 26.87 0.633
17 89.68770 8.144
18 53.87590 9.000 1.80420 46.50 0.558
19 -40.82290 1.800 1.54814 45.78 0.569
20 38.77380 1.890
21 87.46220 4.500 1.77250 49.62 0.550
22*a -67.90670 BF
[Aspheric data]
22nd surface κ=-14.3910
A4=-2.55E-06, A6=6.09E-09, A8=0.00E+00, A10=0.00E+00
[Variable interval data for close-up shooting]
Focused at infinity Focused at close range
f = 48.500 β = -0.180
D8 10.949 0.100
D13 1.508 4.855
[Value corresponding to conditional expression]
Conditional expression (1)
ndN2 + (0.01425 x vdN2) = 2.042
Conditional expressions (2), (2-1), (2-2)
νdN2 = 26.87
Conditional expression (3)
θgFN2+(0.00316×νdN2)=0.7179
Conditional expressions (4), (4-1), (4-2)
ndN2 + (0.00787 x vdN2) = 1.871
Conditional expression (5)
DN2 = 1.600
Conditional expression (6)
ndN2 = 1.65940
Conditional expression (7)
ndN2−(0.040×νdN2−2.470)×νdN2=35.830
Conditional expression (8)
ndN2−(0.020×νdN2−1.080)×νdN2=12.920

FIG. 2 is a diagram of various aberrations in the infinity focused state of the optical system according to the first embodiment. In each aberration diagram, FNO indicates F number and Y indicates image height. The spherical aberration diagram shows the F-number or numerical aperture corresponding to the maximum aperture, the astigmatism diagram and the distortion diagram show the maximum image height, and the coma aberration diagram shows the value of each image height. . d is the d-line (wavelength λ=587
. 6 nm), g is g-line (wavelength λ = 435.8 nm), C is C-line (wavelength λ = 656.3 nm
) and F indicate the F line (wavelength λ=486.1 nm). In the astigmatism diagrams, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. In the aberration diagrams of each example shown below, the same reference numerals as in the present example are used, and redundant description is omitted.

From the various aberration diagrams, it can be seen that the optical system according to the first example has various aberrations well corrected and has excellent imaging performance.

(Second embodiment)
A second embodiment will be described with reference to FIGS. 3 and 4 and Table 2. FIG. FIG. 3 is a diagram showing the lens configuration in the infinity focused state of the optical system according to the second example of the present embodiment. The optical system LS(2) according to the second embodiment includes, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a positive refractive power. and a third lens group G3 having power. During focusing from an infinite distance object to a close (finite distance) object, the second lens group G2 moves along the optical axis toward the image side. An aperture stop S is arranged in the third lens group G3.

The first lens group G1 is cemented with a biconvex positive lens L11, a biconvex positive lens L12, a biconvex positive lens L13, and a biconcave negative lens L14, arranged in order from the object side. and a lens.

The second lens group G2 is composed of a cemented lens composed of a positive meniscus lens L21 having a concave surface facing the object side and a biconcave negative lens L22 arranged in order from the object side.

The third lens group G3 includes a double convex positive lens L31, a cemented lens composed of a double convex positive lens L32 and a double concave negative lens L33, and a double convex positive lens, arranged in order from the object side. L34, a cemented lens composed of a biconcave negative lens L35 and a positive meniscus lens L36 having a convex surface facing the object side, and a cemented lens composed of a biconcave negative lens L37 and a biconvex positive lens L38. Configured. An image plane I is arranged on the image side of the third lens group G3. An aperture stop S is arranged between the negative lens L33 and the positive lens L34 in the third lens group G3. In this embodiment, the positive lens L38 of the third lens group G3 corresponds to the image side lens, and the negative lens L37 of the third lens group G3 corresponds to the negative lens that satisfies the conditional expressions (1) to (3). .

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

(Table 2)
[Overall specifications]
f 102.890
FNO 1.450
2ω 23.554
Y 21.63
TL 150.819
BF 41.316
[Lens specifications]
Surface number R D nd νd θgF
1 234.65900 5.211 1.59349 67.00 0.537
2 -3574.17780 0.100
3 93.58400 9.232 1.49782 82.57 0.539
4 -1217.36840 0.100
5 70.43160 12.063 1.49782 82.57 0.539
6 -224.04700 3.500 1.72047 34.71 0.583
7 171.70550 D7 (variable)
8 -151.55960 4.000 1.65940 26.87 0.633
9 -80.06770 2.500 1.48749 70.32 0.529
10 46.21880 D10 (variable)
11 69.71830 7.132 2.00100 29.13 0.599
12 -255.66290 0.100
13 216.69850 7.584 1.69680 55.52 0.543
14 -52.55750 1.800 1.72825 28.38 0.607
15 31.26990 6.330
16 ∞ 0.600 (Aperture S)
17 88.47780 5.183 1.59319 67.90 0.544
18 -95.38130 1.184
19 -54.31770 1.600 1.65412 39.68 0.574
20 31.94510 7.378 1.79500 45.31 0.560
21 241.73250 1.710
22 -110.87090 1.800 1.65940 26.87 0.633
23 125.19550 5.209 2.00100 29.13 0.599
24 -63.04960 BF
[Variable interval data for close-up shooting]
Focused at infinity Focused at close range
f = 102.890 β = -0.136
D7 7.973 19.973
D10 17.215 5.215
[Value corresponding to conditional expression]
Conditional expression (1)
ndN2 + (0.01425 x vdN2) = 2.042
Conditional expressions (2), (2-1), (2-2)
νdN2 = 26.87
Conditional expression (3)
θgFN2+(0.00316×νdN2)=0.7179
Conditional expressions (4), (4-1), (4-2)
ndN2 + (0.00787 x vdN2) = 1.871
Conditional expression (5)
DN2 = 1.800
Conditional expression (6)
ndN2 = 1.65940
Conditional expression (7)
ndN2−(0.040×νdN2−2.470)×νdN2=35.830
Conditional expression (8)
ndN2−(0.020×νdN2−1.080)×νdN2=12.920

FIG. 4 is a diagram of various aberrations in the infinity focused state of the optical system according to the second embodiment. From the various aberration diagrams, it can be seen that the optical system according to Example 2 is well corrected for various aberrations and has excellent imaging performance.

(Third embodiment)
A third embodiment will be described with reference to FIGS. 5 to 6 and Table 3. FIG. FIG. 5 is a diagram showing the lens configuration in the infinity focused state of the optical system according to the third example of the present embodiment. The optical system LS(3) according to the third embodiment includes, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a negative refractive power. Powerful third lens group G3
and a fourth lens group G4 having positive refractive power. When zooming from the wide-angle end state (W) to the telephoto end state (T), the first to fourth lens groups G1 to G4 move in directions indicated by arrows in FIG. An aperture diaphragm S is disposed between the first lens group G1 and the second lens group G2, and moves along the optical axis together with the second lens group G2 during zooming.

The first lens group G1 includes, in order from the object side, a negative meniscus lens L11 having a convex surface facing the object side, a negative meniscus lens L12 having a convex surface facing the object side, and a biconcave negative lens L13. and a convex positive lens L14. Both lens surfaces of the negative meniscus lens L11 are aspheric. The negative lens L13 has an aspheric lens surface on the image side.

The second lens group G2 includes a cemented lens composed of a negative meniscus lens L21 having a convex surface facing the object side and a positive meniscus lens L22 having a convex surface facing the object side, arranged in order from the object side, and a biconvex positive lens L23. and consists of In this embodiment, the negative meniscus lens L21 of the second lens group G2 corresponds to a negative lens that satisfies conditional expressions (1) to (3).

The third lens group G3 includes a cemented lens composed of a biconvex positive lens L31 and a biconcave negative lens L32 arranged in order from the object side, a negative meniscus lens L33 having a concave surface facing the object side, and a biconvex lens. and a shaped positive lens L34. In this embodiment, the negative meniscus lens L33 and the positive lens L34 of the third lens group G3 move toward the image side along the optical axis when focusing from an infinity object to a short (finite) distance object.

The fourth lens group G4 includes a cemented lens composed of a biconvex positive lens L41 and a biconcave negative lens L42, a biconvex positive lens L43, and a biconvex positive lens arranged in order from the object side. and a cemented lens composed of L44 and a biconcave negative lens L45. An image plane I is arranged on the image side of the fourth lens group G4. In this embodiment, the negative lens L45 of the fourth lens group G4 corresponds to the image side lens. The negative lens L45 has an aspheric lens surface on the image side.

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

(Table 3)
[Overall specifications]
Zoom ratio 2.07
WMT
f 16.65 24.00 34.44
FNO 4.12 4.12 4.18
2ω 53.80 41.66 31.60
Y 21.60 21.60 21.60
TL 168.91 164.50 169.42
BF 39.00 48.25 65.00
[Lens specifications]
Surface number R D nd νd θgF
1*a 157.02850 3.000 1.76684 46.78 0.5576
2*a 19.73150 8.955
3 397.62390 1.550 1.88300 40.66 0.5668
4 51.01700 5.065
5 -57.91430 1.500 1.88300 40.66 0.5668
6 51.94950 0.400 1.55389 38.09 0.5928
7*a 70.15770 1.237
8 44.62150 6.911 1.69895 30.13 0.6021
9 -47.20650 D9 (Variable)
10 ∞ 0.000 (Aperture S)
11 42.61580 1.050 1.74971 24.66 0.6272
12 17.74250 4.132 1.59154 39.29 0.5779
13 75.16900 0.100
14 34.28950 4.194 1.53404 48.26 0.5617
15 -63.55520 D15 (Variable)
16 151.28780 2.518 1.62004 36.40 0.5833
17 -33.01780 1.000 1.88300 40.66 0.5668
18 44.83300 2.756
19 -20.44030 0.800 1.88300 40.66 0.5668
20 -59.69050 0.150
21 151.29690 3.966 1.84666 23.80 0.6215
22 -32.91290 D22 (Variable)
23 34.01270 10.039 1.49782 82.57 0.5386
24 -29.32300 1.100 1.83400 37.18 0.5778
25 71.52300 0.100
26 34.90120 10.548 1.49782 82.57 0.5386
27 -38.97720 0.100
28 40.26640 11.985 1.50377 63.91 0.536
29 -23.35670 1.600 1.80610 40.97 0.5688
30*a-1764.39570 BF
[Aspheric data]
First surface κ=1.0000
A4=3.00E-06, A6=3.39E-09, A8=0.00E+00, A10=0.00E+00
2nd surface κ=1.0000
A4=-2.11E-05, A6=0.00E+00, A8=0.00E+00, A10=0.00E+00
7th surface κ=1.0000
A4=1.75E-05, A6=-2.74E-08, A8=1.77E-11, A10=0.00E+00
30th surface κ=1.0000
A4=1.53E-05, A6=8.95E-09, A8=0.00E+00, A10=0.00E+00
[Variable interval data for zooming]
WMT
D9 29.355 13.227 2.000
D15 6.263 12.605 16.459
D22 9.534 5.666 1.200
[Lens group data]
Group Starting surface Focal length
G1 1 -23.700
G2 10 41.700
G3 16 -62.000
G4 23 49.100
[Value corresponding to conditional expression]
Conditional expression (1)
ndN2 + (0.01425 x vdN2) = 2.101
Conditional expressions (2), (2-1), (2-2)
νdN2 = 24.66
Conditional expression (3)
θgFN2+(0.00316×νdN2)=0.7051
Conditional expressions (4), (4-1), (4-2)
ndN2 + (0.00787 x vdN2) = 1.944
Conditional expression (5)
DN2 = 1.050
Conditional expression (6)
ndN2 = 1.74971
Conditional expression (7)
ndN2−(0.040×νdN2−2.470)×νdN2=34.836
Conditional expression (8)
ndN2−(0.020×νdN2−1.080)×νdN2=12.721

6(A), 6(B), and 6(C) respectively show the wide-angle end state, intermediate focal length state, and telephoto end state of the optical system according to the third embodiment when focusing on infinity. It is an aberration diagram. From the various aberration diagrams, it can be seen that the optical system according to the third example is well corrected for various aberrations and has excellent imaging performance.

(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 the lens configuration in the infinity focused state of the optical system according to the fourth example of this embodiment. The optical system LS(4) according to the fourth example includes, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a positive refractive power. Consists of a third lens group G3 having power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having negative refractive power, and a sixth lens group G6 having negative refractive power. It is When zooming from the wide-angle end state (W) to the telephoto end state (T), the first to fifth lens groups G1 to G5 move in directions indicated by arrows in FIG. An aperture stop S is arranged in the second lens group G2.

The first lens group G1 includes a cemented lens composed of a negative meniscus lens L11 having a convex surface facing the object side and a biconvex positive lens L12 arranged in order from the object side, and a positive meniscus lens L13 having a convex surface facing the object side. and consists of A diffractive optical element DOE is arranged on the image-side lens surface of the positive meniscus lens L13. The diffractive optical element DOE is, for example, a contact multi-layer type diffractive optical element in which two kinds of diffraction element elements made of different materials are in contact with the same diffraction grating groove. A first-order diffraction grating (rotationally symmetrical diffraction grating with respect to the optical axis) is formed.

The second lens group G2 includes a cemented lens composed of a biconcave negative lens L21 and a positive meniscus lens L22 having a convex surface facing the object side, arranged in order from the object side, and a positive meniscus lens L23 having a concave surface facing the object side. and a positive meniscus lens L24 having a convex surface facing the object side. An aperture stop S is arranged between the positive meniscus lens L23 and the positive meniscus lens L24 in the second lens group G2. The cemented lens composed of the negative lens L21 and the positive meniscus lens L22 of the second lens group G2 and the positive meniscus lens L23 form a vibration reduction lens group (partial group) that is movable in a direction perpendicular to the optical axis. Displacement of the imaging position (image blur on the image plane I) due to blurring or the like is corrected.

The third lens group G3 is composed of, in order from the object side, a negative meniscus lens L31 having a convex surface facing the object side and a biconvex positive lens L32.

The fourth lens group G4 is composed of a cemented lens composed of a biconvex positive lens L41 and a negative meniscus lens L42 having a concave surface facing the object side, arranged in order from the object side.

The fifth lens group G5 is composed of a cemented lens composed of a biconvex positive lens L51 and a biconcave negative lens L52 arranged in order from the object side. In this embodiment, focusing is performed by moving the entire fifth lens group G5 along the optical axis.

The sixth lens group G6 includes, in order from the object side, a cemented lens composed of a negative meniscus lens L61 having a convex surface facing the object side and a biconvex positive lens L62; a biconcave negative lens L63; and a negative meniscus lens L64 with a concave surface directed toward the . An image plane I is arranged on the image side of the sixth lens group G6. In this embodiment, the negative meniscus lens L64 of the sixth lens group G6 corresponds to the image side lens, and the negative meniscus lens L61 of the sixth lens group G6 is a negative lens that satisfies the conditional expressions (1) to (3). Applicable.

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

(Table 4)
[Overall specifications]
Zoom ratio 2.00
WMT
f 199.985 300.128 400.487
FNO 5.770 5.773 7.777
2ω 12.088 8.032 3.016
Y 21.60 21.60 21.60
TL 218.509 276.018 309.437
BF 63.575 63.605 63.797
[Lens specifications]
Surface number R D nd νd θgF
1 338.9295 3.0000 1.806100 33.34
2 157.1292 7.1098 1.487490 70.32
3 -645.1901 0.1000
4 127.7241 6.3846 1.516800 64.13
5*b 1000.0000 D5 (variable)
6 -122.6329 1.7000 1.743997 44.79
7 65.7202 3.5689 1.659398 26.87 0.6323
8 249.7691 15.0000
9 -47.9778 3.5000 1.756462 24.89 0.6196
10 -45.0509 2.2932
11 ∞ 0.5000 (Aperture S)
12 43.2479 2.9936 1.620041 36.26
13 64.4050 D13 (variable)
14 82.9323 1.7000 1.808090 22.74
15 46.2622 3.6463
16 71.4836 4.1939 1.612720 58.54
17 -405.4059 D17 (Variable)
18 56.3851 6.9255 1.497820 82.57
19 -60.8758 1.7000 1.755000 52.33
20 -374.3030 D20 (Variable)
21 102.7274 2.4918 1.592701 35.31
22 -125.8788 1.0000 1.755000 52.33
23 40.8982 D23 (variable)
24 121.6273 1.7000 1.659398 26.87 0.6323
25 52.1810 5.7438 1.595510 39.21
26 -42.4345 0.1000
27 -97.3797 1.5000 1.456000 91.37
28 59.1706 12.2493
29 -26.6286 1.5000 1.755000 52.33
30 -37.6940 BF
[Diffraction surface data]
5th surface λ0 = 587.6
m=1
Ｃ2＝-2.57E-05
Ｃ4＝-2.04E-11
[Variable interval data for zooming]
WMT
D5 11.860 93.192 119.742
D13 10.900 0.500 3.244
D17 0.600 5.172 0.600
D20 34.411 13.877 0.200
D23 6.561 9.070 31.254
[Lens group data]
Group Starting surface Focal length
G1 1 213.671
G2 6-546.584
G3 14 370.319
G4 18 149.206
G5 21-72.703
G6 24-875.523
[Value corresponding to conditional expression]
Conditional expression (1)
ndN2 + (0.01425 x vdN2) = 2.042
Conditional expressions (2), (2-1), (2-2)
νdN2 = 26.87
Conditional expression (3)
θgFN2+(0.00316×νdN2)=0.7172
Conditional expressions (4), (4-1), (4-2)
ndN2 + (0.00787 x vdN2) = 1.871
Conditional expression (5)
DN2 = 1.7000
Conditional expression (6)
ndN2 = 1.659398
Conditional expression (7)
ndN2−(0.040×νdN2−2.470)×νdN2=35.830
Conditional expression (8)
ndN2−(0.020×νdN2−1.080)×νdN2=12.920

8(A), 8(B), and 8(C) respectively show the wide-angle end state, the intermediate focal length state, and the telephoto end state of the optical system according to the fourth embodiment when focusing on infinity. It is an aberration diagram. From the various aberration diagrams, it can be seen that the optical system according to the fourth example is well corrected for various aberrations and has excellent imaging performance.

(Fifth embodiment)
A fifth embodiment will be described with reference to FIGS. 9 to 10 and Table 5. FIG. FIG. 9 is a diagram showing the lens configuration in the infinity focused state of the optical system according to the fifth example of this embodiment. The optical system LS(5) according to the fifth embodiment includes, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a positive refractive power. and a third lens group G3 having power. When focusing from an infinity object to a short distance (finite distance) object, the second lens group G2 and the third lens group G3 move by different amounts of movement toward the object side along the optical axis. An aperture stop S is disposed between the second lens group G2 and the third lens group G3, and moves along the optical axis together with the third lens group G3 during focusing.

The first lens group G1 is a cemented lens composed of a positive meniscus lens L11 having a convex surface facing the object side and a negative meniscus lens L12 having a convex surface facing the object side, arranged in order from the object side, and a cemented lens having a concave surface facing the object side. It is composed of a cemented lens composed of a positive meniscus lens L13 and a biconcave negative lens L14, and a biconvex positive lens L15.

The second lens group G2 is composed of, in order from the object side, a biconvex positive lens L21 and a cemented lens composed of a biconvex positive lens L22 and a biconcave negative lens L23.

The third lens group G3 is a cemented lens composed of a positive meniscus lens L31 with a concave surface facing the object side and a biconcave negative lens L32 arranged in order from the object side, a biconvex positive lens L33 and a biconcave lens. and a biconvex positive lens L35. An image plane I is arranged on the image side of the third lens group G3. In this embodiment, the positive lens L35 of the third lens group G3 corresponds to the image side lens, and the negative lens L32 of the third lens group G3 corresponds to the negative lens that satisfies the conditional expressions (1) to (3). . The positive lens L35 has an aspheric lens surface on the image side.

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

(Table 5)
[Overall specifications]
f48.500
FNO 1.405
2ω 48.286
Y 21.63
TL 142.000
BF 38.800
[Lens specifications]
Surface number R D nd νd θgF
1 52.54160 7.000 2.00100 29.13 0.599
2 110.48020 2.500 1.54814 45.78 0.569
3 26.51260 13.200
4 -54.54930 6.000 1.49700 81.61 0.539
5 -28.35840 2.000 1.61266 44.46 0.564
6 89.06350 2.911
7 87.07170 7.500 1.72916 54.61 0.544
8 -56.49940 D8 (Variable)
9 176.92530 4.500 2.00100 29.13 0.599
10 -163.53030 0.100
11 68.43160 7.500 1.49700 81.61 0.539
12 -56.04760 1.800 1.64769 33.72 0.593
13 91.91670 D13 (variable)
14 ∞ 3.504 (Aperture S)
15 -71.98140 4.000 1.49782 82.57 0.539
16 -32.38870 1.600 1.61155 31.26 0.618
17 95.98930 6.985
18 53.08170 9.000 1.80420 46.50 0.558
19 -41.18080 1.800 1.54814 45.78 0.569
20 38.38990 2.090
21 95.28680 4.500 1.77250 49.62 0.550
22*a -65.98280 BF
[Aspheric data]
22nd surface κ=-14.2137
A4=-2.94E-06, A6=6.71E-09, A8=0.00E+00, A10=0.00E+00
[Variable interval data for close-up shooting]
Focused at infinity Focused at close range
f = 48.500 β = -0.180
D8 11.533 0.100
D13 3.177 7.097
[Value corresponding to conditional expression]
Conditional expression (1)
ndN2 + (0.01425 x vdN2) = 2.057
Conditional expressions (2), (2-1), (2-2)
νdN2 = 31.26
Conditional expression (3)
θgFN2+(0.00316×νdN2)=0.7173
Conditional expressions (4), (4-1), (4-2)
ndN2 + (0.00787 x vdN2) = 1.858
Conditional expression (5)
DN2 = 1.600
Conditional expression (6)
ndN2 = 1.61155
Conditional expression (7)
ndN2−(0.040×νdN2−2.470)×νdN2=36.513
Conditional expression (8)
ndN2−(0.020×νdN2−1.080)×νdN2=12.605

10A and 10B are various aberration diagrams of the optical system according to the fifth embodiment in the infinity focused state. From the various aberration diagrams, it can be seen that the optical system according to the fifth example is well corrected for various aberrations and has excellent imaging performance.

According to each of the above-described embodiments, it is possible to realize an optical system in which, in correction of chromatic aberration, in addition to the primary achromatization, the secondary spectrum is well corrected.

Here, each of the above embodiments shows one specific example of the present invention, and the present invention is not limited to these.

It should be noted that the following content can be appropriately employed within a range that does not impair the optical performance of the optical system of this embodiment.

Focusing lens group shall refer to a portion having at least one lens separated by an air gap that varies during focusing. That is, a single lens group, a plurality of lens groups, or a partial lens group may be moved in the optical axis direction to form a focusing lens group that performs focusing from an object at infinity to an object at a short distance. This focusing lens group can also be applied to autofocus, and is also suitable for motor drive (using an ultrasonic motor or the like) for autofocus.

In the fourth example of the optical system of the present embodiment, a configuration having a vibration isolation function is shown, but the present application is not limited to this, and a configuration without a vibration isolation function is also possible. Also, other embodiments that do not have a vibration isolation function can be configured to have a vibration isolation function.

The lens surface may be spherical, planar, or aspherical. A spherical or flat lens surface is preferable because it facilitates lens processing and assembly adjustment and prevents degradation of optical performance due to errors in processing and assembly adjustment. Also, even if the image plane is deviated, there is little deterioration in rendering performance, which is preferable.

If the lens surface is aspherical, the aspherical surface can be ground aspherical, glass-molded aspherical, which is formed into an aspherical shape from glass, or composite aspherical, which is formed into an aspherical shape from resin on the surface of glass. It doesn't matter which one. Further, the lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

Each lens surface may be provided with an anti-reflection film having high transmittance over a wide wavelength range in order to reduce flare and ghost and achieve high-contrast optical performance. As a result, flare and ghost can be reduced, and high contrast and high optical performance can be achieved.

G1 1st lens group G2 2nd lens group G3 3rd lens group G4 4th lens group G5 5th lens group G6 6th lens group I Image plane S Aperture diaphragm

Claims (1)

An optical system having an aperture stop and a negative lens disposed on the image side of the aperture stop and satisfying the following conditional expression.
ndN2+(0.01425×νdN2)<2.12
18.0<νdN2<35.0
0.702<θgFN2+(0.00316×νdN2)
where ndN2: the refractive index of the negative lens for the d-line; νdN2: the Abbe number of the negative lens with respect to the d-line; θgFN2=(ngN2−nFN2)/(nFN2−nCN2) where nFN2 is the refractive index of the negative lens for the F line and nCN2 is the refractive index of the negative lens for the C line.

Images