JP2017102352A - Optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which: in a gaussian optical system, the weight of an optical system increases as its performance is to be improved, and therefore, it is difficult to achieve both improved performance and weight saving.SOLUTION: In a gaussian optical system, a rear group is constituted by a negative lens, a positive lens, a positive lens, a negative lens, and a positive lens, and a set of adjacent positive lens and negative lens of the rear group is made of resin material, and applied with proper refractive power.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical system, and is suitable for an imaging optical system used in an imaging apparatus such as a silver salt film camera, a digital still camera, a video camera, and a digital video camera.

  Conventionally, a Gaussian optical system is used as a photographing lens having a photographing field angle of about 45 degrees. Patent Document 1 describes a six-element Gaussian optical system. Gauss-type lenses have the feature that they are easy to increase in diameter with a small number of lenses, but the imaging performance deteriorates due to spherical aberration, coma, sagittal halo, and axial chromatic aberration (especially the secondary spectrum of axial chromatic aberration). There was a problem.

  As a means of correcting spherical aberration and coma aberration, a method using an aspherical surface in the rear group from the stop is known, and as a means of correcting sagittal halo, a negative lens is added and the curvature of concave surfaces on both sides sandwiching the stop is added. There is a known technique for loosening. As a means for correcting the secondary spectrum of longitudinal chromatic aberration, there is known a method of selecting a glass material having a large anomalous partial dispersion for a positive lens and a glass material having a small anomalous partial dispersion for a negative lens (Patent Document 1). reference).

JP-A-62-87922

  However, when an aspherical surface or a concave surface is adopted, the number of lenses increases and the weight of the optical system increases.

  Normally, since the performance change due to focusing is small in a Gaussian optical system, focusing is performed by the entire extension. Therefore, when the number of lenses increases, the problem that the torque required for focusing increases has occurred.

  Accordingly, an object of the present invention is to provide an optical system that suppresses an increase in weight as much as possible while achieving high performance.

In order to achieve the above object, an optical system according to the present invention includes:
In order from the object side, there are a front group, a stop, and a rear group, and the rear group has a negative lens, a positive lens, a positive lens, a negative lens, and a positive lens, and the adjacent positive lens LP and negative lens LN in the rear group. These groups are made of a resin material, and at least one surface of the resin lens has an aspherical surface and satisfies the following conditional expression.

−1.6 <fp / fn <−0.6
Here, fp is the focal length of the positive lens LP, and fn is the focal length of the negative lens LN.

  According to the present invention, a high-performance and lightweight optical system in which spherical aberration, coma aberration, and sagittal halo are corrected can be obtained.

1 is a cross-sectional view of an optical system in an infinitely focused state according to Embodiment 1. FIG. FIG. 4 is a longitudinal aberration diagram in Example 1 at an infinite focus state. FIG. 4 is a lateral aberration diagram in the in-focus state according to Example 1. 6 is a cross-sectional view of an optical system in an infinitely focused state according to Embodiment 2. FIG. FIG. 6 is a longitudinal aberration diagram in Example 2 when focused on infinity. FIG. 6 is a lateral aberration diagram in Example 2 when in infinity focus. FIG. 6 is a cross-sectional view of the optical system in an infinitely focused state according to Example 3. FIG. 6 is a longitudinal aberration diagram in Example 3 at an infinite focus state. FIG. 6 is a transverse aberration diagram for Example 3 at the infinite focus state. It is an example of the optical apparatus of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Optical system)
In the embodiment of the present invention, in order to suppress an increase in weight while correcting spherical aberration, coma aberration, and sagittal halo, which are the characteristics of the aberration of the Gaussian optical system, in order from the object side, the front group, the aperture, and the rear The rear group includes a negative lens, a positive lens, a positive lens, a negative lens, and a positive lens, and a pair of a positive lens LP and a negative lens LN adjacent to each other in the rear group is made of a resin material. At least one of the surfaces has an aspherical surface.

  In each optical system sectional view, SP represents an aperture stop, and IP represents an image plane. In each longitudinal aberration diagram (FIGS. 2, 5, and 8), the solid line is the d-line meridional ray, the broken line is the d-line sagittal ray, the long broken line is the F-line, the one-dot chain line is the C-line, and the two-dot chain line is The g line is shown. In each lateral aberration diagram (FIGS. 3, 6, and 9), the solid line is the d-line meridional ray, the broken line is the d-line sagittal ray, the long broken line is the F-line meridional ray, and the alternate long and short dash line is the C-line meridional ray. Rays and two-dot chain lines represent g-line meridional rays.

(Specific configuration)
The embodiment of the present invention will be described by taking Example 1 as an example.

  As shown in FIG. 1, compared to the basic six-element Gauss optical system, one positive lens and one negative lens are added to the rear group. Mainly sagittal halo correction by correcting aberrations and adding a negative lens. Further, by setting the lens configuration of the rear group to be negative, positive, positive, or negative, the lateral aberration undulation of the off-axis meridional ray is reduced.

  Further, in order to suppress an increase in the weight of the optical system due to the addition of the number of lenses as much as possible, a pair of adjacent positive and negative lenses (LP and LN in FIG. 1) among the negative, positive, positive, and positive lenses are resin lenses made of a resin material. . Generally, the specific gravity of a glass material used in an optical system is 2.5 to 5.5, and the specific gravity of a resin material is about 1.0 to 1.3. Weight increase can be prevented to about 5.5.

  Further, when using the resin lens, at least one surface is aspherical so that mainly spherical aberration and coma can be corrected.

Conditional expression (1) is a condition for suppressing performance deterioration due to a temperature change when using a resin lens.
−1.6 <fp / fn <−0.6 (1)
In this embodiment, since a pair of adjacent lenses is made of a resin lens, the adjacent lenses are close to each other in variation due to a temperature change with respect to each aberration such as spherical aberration, coma aberration, and astigmatism. Therefore, it is configured to cancel those changes. Conditional expression (1) is an expression that defines the range of the refractive power of the positive and negative lenses that can cancel each aberration satisfactorily.

  In the present embodiment, the following conditions may be further satisfied.

1.50 <Nn <1.7 (2)
30 <νn <15 (3)
| ΘgF − (− 1.665 × 10 ⁻⁷ · νp ³ + 5.214 × 10 ⁻⁵ · νp ² −5.656 × 10 ⁻³ · νp + 0 · 7278) |> 0.03 (4)
Here, Nn and νn in the conditional expressions (2) and (3) are the refractive index and Abbe number of the resin negative lens LN, respectively. By satisfying conditional expressions (2) and (3), it is possible to correct both primary axial chromatic aberration and field curvature.

  In the conditional expression (4), νp and θgF are the Abbe number and partial dispersion ratio of the resin positive lens LP, respectively. By using a resin positive lens that satisfies the conditional expression (4), the secondary spectrum of longitudinal chromatic aberration can be corrected well.

  Next, more specific details of each embodiment will be described.

Example 1
Example 1 is a large-diameter Gaussian optical system having a total angle of view of 45.5 ° and an aperture ratio of 1.85. FIG. 1 is a sectional view of an optical system according to the first embodiment. The configuration of the rear group is negative, positive and negative from the aperture of the optical system, and the third lens (LP) and the fourth lens (LN) in the rear group are made of resin lenses to reduce the weight. Yes.

  2 and 3 are a longitudinal aberration diagram and a lateral aberration diagram, respectively, at the time of focusing on infinity according to Example 1. FIG. From the lateral aberration diagram, it can be seen that spherical aberration, coma aberration, and sagittal halo are well corrected by the configuration of the present invention. In Example 1, the material satisfying the conditional expression (4) is used for the resin positive lens, so that the secondary spectrum of longitudinal chromatic aberration, which is a problem with a large-aperture lens, is corrected favorably. In the first embodiment, the focusing is performed by the entire extension.

(Example 2)
The second embodiment is a large-diameter Gaussian optical system having a total angle of view of 46 ° and an aperture ratio of 1.85. FIG. 4 is a sectional view of an optical system according to the second embodiment. The configuration of the rear group is negative, positive and negative from the aperture of the optical system, and the third lens (LP) and the fourth lens (LN) in the rear group are made of resin lenses to reduce the weight. Yes.

  5 and 6 are a longitudinal aberration diagram and a lateral aberration diagram, respectively, at the time of focusing on infinity according to Example 2. FIG. From the lateral aberration diagram, it can be seen that spherical aberration, coma aberration, and sagittal halo are well corrected by the configuration of the present invention. In addition, Example 2 is also configured to perform focusing by the entire extension.

(Example 3)
Example 3 is a large-aperture Gaussian optical system having a total angle of view of 47.7 ° and an aperture ratio of 1.85. Since the sensor size of the third embodiment is smaller than those of the first and second embodiments, the focal length is shorter even at the same angle of view. FIG. 7 is a sectional view of an optical system according to the third embodiment. The configuration of the rear group is negative, positive and negative from the aperture of the optical system, and the third lens (LP) and the fourth lens (LN) in the rear group are made of resin lenses to reduce the weight. Yes. In Example 3, the negative lens is disposed closest to the object side so that the back focus can be secured even when the focal length is shortened.

  8 and 9 are a longitudinal aberration diagram and a lateral aberration diagram, respectively, at the time of focusing on infinity according to Example 3. FIG. From the lateral aberration diagram, it can be seen that spherical aberration, coma aberration, and sagittal halo are well corrected by the configuration of the present invention. In Example 3, a material satisfying conditional expression (4) is used for the resin positive lens, so that the secondary spectrum of longitudinal chromatic aberration, which is a problem with a large aperture lens, is corrected well. In the third embodiment, focusing is performed by driving the rear group from the stop.

(Optical equipment)
Next, a single-lens reflex camera system as an optical apparatus using the optical system of the present invention will be described with reference to FIG.

  In FIG. 10, 10 is a single-lens reflex camera body, and 11 is an interchangeable lens equipped with an optical system according to the present invention. Reference numeral 12 denotes a recording unit such as a film or an image sensor for recording a subject image obtained through the interchangeable lens 11.

  Reference numeral 13 denotes a finder optical system for observing a subject image from the interchangeable lens 11, and reference numeral 14 denotes a rotating quick return mirror for switching and transmitting the subject image from the interchangeable lens 11 to the recording means 12 and the finder optical system 13. When observing the subject image with the finder, the subject image formed on the focusing plate 15 via the quick return mirror 14 is made into an erect image with the pentaprism 16 and then magnified and observed with the eyepiece optical system 17.

  At the time of shooting, the quick return mirror 14 rotates in the direction of the arrow, and the subject image is formed and recorded on the recording means 12. Reference numeral 18 denotes a submirror, and 19 denotes a focus detection device.

  Thus, by applying the optical system of the present invention to an optical apparatus such as a single-lens reflex camera interchangeable lens, an optical apparatus having high optical performance can be realized.

  The present invention can be similarly applied to a single-lens reflex camera without a quick return mirror, and is not limited to the above.

(Numeric data)
Next, numerical data of each example is shown. In the numerical data of each embodiment, j represents the surface number counted from the object side, Aj is the effective ray diameter of the j-th surface, Rj is the radius of curvature of the j-th surface number, and Dj is the j-th surface. The surface spacing on the optical axis with respect to the (j + 1) th surface, Nj, and νj represent the refractive index and Abbe number of the jth optical material with respect to the d-line. f is the focal length of the optical system, Fno is the aperture ratio, and ω is the half angle of view. The object distance is a distance from the first lens surface to the object.

The aspherical shape is such that X is the amount of variation from the surface vertex in the optical axis direction, r is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and C _2. , C ₄ , C ₆ ,... Are represented by the following formulas when each order has an aspherical shape.

“E ± YY” in each coefficient means “× 10 ^{± YY} ”.

  In addition, Table 1 shows values of the mathematical expressions in the respective examples.

Example 1
Unit mm

Surface data surface number rd nd vd
1 ∞ 1.50
2 76.512 2.28 1.77250 49.6
3 2252.687 0.98
4 21.060 3.62 1.91082 35.3
5 33.236 0.72
6 45.139 1.50 1.69895 30.1
7 16.188 6.33
8 (Aperture) ∞ 10.07
9 -17.806 1.20 1.78472 25.7
10 82.121 6.30 1.91082 35.3
11 -24.198 0.15
12 ∞ 0.15
13 * 115.710 2.72 1.64040 18.9
14 * -174.532 0.42
15 ∞ 0.87
16 * -145.825 1.33 1.63550 23.9
17 * 64.751 0.50
18 75.657 4.48 1.71300 53.9
19 -56.206 39.08
Image plane ∞

Aspherical data 13th surface
K = 0.00000e + 000 A 4 = 5.96541e-006 A 6 = -2.19619e-009 A 8 = -8.70305e-011 A10 = 3.77296e-013 A12 = -1.79666e-015

14th page
K = 0.00000e + 000 A 4 = -2.06965e-006 A 6 = -1.69639e-008 A 8 = 6.55986e-011 A10 = -6.06680e-013 A12 = 7.59519e-016

16th page
K = 0.00000e + 000 A 4 = -7.04652e-006 A 6 = 9.64507e-009 A 8 = -9.56133e-011 A10 = 4.38713e-013 A12 = -5.10048e-016

17th page
K = 2.85938e + 000 A 4 = 2.68804e-006 A 6 = -4.15995e-009 A 8 = 5.69152e-011 A10 = -1.68831e-013 A12 = 5.51959e-017

Focal length 51.60
F number 1.85
Angle of View 22.75
Statue height 21.64
Total lens length 84.19
BF 39.08

(Example 2)
Unit mm

Surface data surface number rd nd vd
1 ∞ 1.50
2 78.830 2.86 1.91082 35.3
3 900.346 0.81
4 21.780 3.96 1.91082 35.3
5 37.035 0.74
6 51.127 1.50 1.78472 25.7
7 16.686 6.18
8 (Aperture) ∞ 10.05
9 -15.968 1.36 1.71736 29.5
10 -4726.643 5.33 1.91082 35.3
11 -22.767 0.15
12 ∞ 0.60
13 * -142.353 2.43 1.53110 55.9
14 * -44.730 0.36
15 ∞ 0.24
16 * -1131.678 1.31 1.63550 23.9
17 * 136.343 0.27
18 158.245 3.61 1.62041 60.3
19 -55.388 39.81
Image plane ∞

Aspherical data 13th surface
K = 0.00000e + 000 A 4 = 2.38664e-006 A 6 = 3.21106e-009 A 8 = -3.33413e-011 A10 = 6.07956e-013 A12 = -1.64198e-015

14th page
K = 0.00000e + 000 A 4 = 1.75371e-006 A 6 = -4.92213e-009 A 8 = 1.45728e-010 A10 = -5.23855e-013 A12 = 5.15484e-016

16th page
K = 0.00000e + 000 A 4 = -2.58557e-006 A 6 = 2.18823e-008 A 8 = -1.04419e-010 A10 = 5.62841e-013 A12 = -1.68222e-015

17th page
K = -1.81128e + 000 A 4 = 2.73906e-007 A 6 = -3.26079e-009 A 8 = 1.01913e-010 A10 = -4.05627e-013 A12 = 4.17291e-016

Focal length 50.97
F number 1.85
Angle of view 23.00
Statue height 21.64
Total lens length 83.07
BF 39.81

(Example 3)
Unit mm

Surface data surface number rd nd vd
1 85.722 1.26 1.90366 31.3
2 22.464 8.12
3 49.575 2.62 1.90366 31.3
4 -355.421 0.45
5 23.453 4.97 1.79952 42.2
6 -139.095 0.23
7 -448.615 1.08 1.51742 52.4
8 15.431 5.75
9 (Aperture) ∞ 9.95
10 -13.896 1.06 1.84666 23.8
11 -947.509 5.09 1.73400 51.5
12 -18.012 0.15
13 * 51.882 1.75 1.64040 18.9
14 103.200 0.15
15 103.200 1.08 1.63550 23.9
16 * 43.739 1.03
17 74.305 4.26 1.77250 49.6
18 -31.978 35.50
Image plane ∞

Aspherical data 13th surface
K = 0.00000e + 000 A 4 = 1.65289e-005 A 6 = 6.72794e-008 A 8 = -1.16475e-009 A10 = 2.82390e-012 A12 = 3.23422e-015

16th page
K = 0.00000e + 000 A 4 = 2.53103e-005 A 6 = 2.00776e-008 A 8 = -6.63262e-010 A10 = 2.97054e-013 A12 = 6.99271e-015

Focal length 30.90
F number 1.85
Angle of view 23.85
Statue height 13.66
Total lens length 84.50
BF 35.50

LP resin lens with positive refractive power of the present invention, LN resin lens with negative refractive power of the present invention,
SP Aperture stop, IP image plane

Claims (3)

In order from the object side, there are a front group, a stop, and a rear group, and the rear group has a negative lens, a positive lens, a positive lens, a negative lens, and a positive lens, and a set of adjacent positive and negative lenses in the rear group. Is made of a resin material, and at least one surface of the resin lens has an aspheric surface, and satisfies the following conditional expression.
−1.6 <fp / fn <−0.6
Here, fp is the focal length of the resin positive lens, and fn is the focal length of the resin negative lens. 2. The optical system according to claim 1, wherein the following conditional expression is satisfied when the refractive index of the resin negative lens is Nn and the Abbe number is νn.
1.50 <Nn <1.7
30 <νn <15 2. The optical system according to claim 1, wherein the following conditional expression is satisfied, where an Abbe number of the resin positive lens is νp and a partial dispersion ratio is θgF.
| ΘgF − (− 1.665 × 10 ⁻⁷ · νp ³ + 5.214 × 10 ⁻⁵ · νp ² −5.656 × 10 ⁻³ · νp + 0 · 7278) |> 0.03