JPH10339842A - Aspherical optical system for infrared rays - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical system excellently compensating for aberration on the entire sereen in spite of the optical system is constituted of a small number of lenses such as two lenses by optimizing the parameters of a positive meniscus lens and a planoconcave lens according to specified conditions. SOLUTION: This system is constituted of two lenses, that is, the positive meniscus lens L1 constituted of germanium and the planoconcave lens L2 constituted of zinc selenid, and the aspherical surface is introduced to the respective lenses L1 and L2 in order to balancedly compensate the aberration. Then, the lenses L1 and L3 are optimized by five conditions, that is, 0.955<f1/f<0.975, -3.35<f2/f<-3.20, 0.68<d/f<0.80, 0.065<t1/f<0.080 and 0.19<t2/f<0.05. In the expressions, (f) means the focal distance of the entire aspherical optical system for infrared, and f1 and f2 mean the focal distances of the lenses L1 and L2, respectively. (d) means a spacing from the lens L1 to the lens L2, and t1 and t2 mean the axial rise of the lenses L1 and L2, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared imaging optical system using a wavelength band of about 7 to 13 .mu.m.

[0002]

2. Description of the Related Art Conventionally, as this kind of infrared optical system, for example, JP-A-52-86344 and JP-A-57-2000
No. 10 is known. Each of the infrared optical systems disclosed in these publications has a configuration of about three sheets and uses only a spherical surface.

[0003]

Although the three-element optical system shown in the above-mentioned prior art has a relatively small number of components, it is necessary to reduce the weight and cost of the infrared system. However, further weight reduction and cost reduction have been demanded. The present invention has been made in view of such a point, and an object of the present invention is to provide an optical system in which aberrations are favorably corrected over the entire screen despite the extremely small number of components such as two.

[0004]

In order to achieve the above object, an infrared aspherical optical system according to the present invention comprises, in order from the object side, a spherical lens surface having a convex surface facing the object side and an image surface side. A positive meniscus lens having an aspheric lens surface with a concave surface facing the lens and made of germanium; the lens surface on the object side is flat, and the lens surface on the image side is concave on the image side And a plano-concave lens made of zinc selenide, which satisfies the following conditions.

(1) 0.955 <f1 / f <0.975 (2) −3.35 <f2 / f <−3.20 (3) 0.68 <d / f <0.80 (4) 0.065 <t1 / f <0.080 (5) 0.19 <t2 / f <0.05, where f: focal length of the entire infrared aspherical optical system, f1: focal length of the positive meniscus lens, f2 : The focal length of the plano-concave lens, d: the distance from the image-side lens surface of the positive meniscus lens to the image-side lens surface of the plano-concave lens, t1: the axial thickness of the positive meniscus lens lens, t2: the axial thickness of the plano-concave lens is there.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the present invention is based on a two-element structure of a positive meniscus lens made of germanium and a plano-concave lens made of zinc selenide, and corrects various aberrations in a well-balanced manner. For this purpose, an aspherical surface is introduced into each lens, and the parameters of each lens are set in the above conditions (1) to
It is optimized by (5). In addition, since the second lens has a plano-concave shape, manufacturing and adjustment are easy, and productivity can be increased.

In the optical system of the present invention, two aspherical surfaces are conveniently introduced at a predetermined interval, so that both on-axis monochromatic aberration and off-axis monochromatic aberration can be corrected well. Is possible. In the present invention, the above condition (1)
According to (3), the refractive power distribution between the positive meniscus lens as the first lens and the plano-concave lens as the second lens,
The interval is specified. These conditions (1) to (3) are conditions for correcting axial chromatic aberration and lateral chromatic aberration that cannot be corrected by an aspheric surface in a well-balanced manner. If these conditions (1) to (3) are not satisfied at the same time, However, it is impossible to achieve satisfactory correction of the axial and lateral chromatic aberrations.

The condition (4) is for defining the thickness of the positive meniscus lens as the first lens. If the upper limit of the condition (4) is exceeded, the positive meniscus lens becomes too thick and the cost of the glass material increases. . On the other hand, if the lower limit is exceeded,
Manufacturing difficulties such as the edge thickness of the positive meniscus lens being unable to be obtained are caused. The condition (5) defines the thickness of the plano-concave lens as the second lens, and the condition (5)
If the condition is not satisfied, even if the above conditions (1) to (3)
However, it is not possible to achieve both the correction of axial chromatic aberration and the correction of lateral chromatic aberration at the same time.

In the present invention, the above condition (1)
In addition to (5), it is preferable that the following condition (6) is satisfied. (6) 0.98 <TL / f <1.11 where TL is the distance (total length) from the object side lens surface of the positive meniscus lens to the image plane.

The condition (6) satisfies both achievement of compactness of the entire optical system and satisfactory correction of coma. If the value exceeds the upper limit of the condition (6), it is not possible to reduce the size of the entire optical system. If the value exceeds the lower limit, coma aberration occurs, which is not preferable.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A numerical embodiment according to the present invention will be described below with reference to the drawings. FIGS. 1 to 4 are lens cross-sectional views of the aspherical optical system for infrared light of the first to fourth embodiments. Each of the embodiments includes two lenses: a positive meniscus lens L1 disposed closest to the object side and having a convex surface facing the object side, and a plano-concave lens L2 disposed closest to the image side and having a concave surface facing the image side. Have. The positive meniscus lens L1 is made of germanium, and has an aspheric surface on the image side. The plano-concave lens L2 is made of zinc selenide, and has an aspheric surface on the image side.

In each of the embodiments, the object side lens surface of the positive meniscus lens L1 as the first lens is at the stop position. Thus, the aspherical surface provided on the positive meniscus lens L1 mainly corrects axial aberration, and the aspherical surface provided on the plano-concave lens L2 corrects mainly off-axis aberration. The following Tables 1 to 4 show values of specifications of the first to fourth embodiments. In each table, the F-number FNO, the focal length f, and the diameter φ of the stop are shown together. The aspheric shape in each embodiment is given by the following equation (1), and each table also shows aspheric data.

[0013]

(Equation 1)

Where X (y): distance along the optical axis from the tangent plane at the lens vertex to the aspherical surface y: height from the optical axis of the aspherical surface k: conical constant AN: aspherical coefficient C: curvature r : Radius of curvature at the vertex of the lens.

In each table, “× 10M” means 1
It indicates that it is 0 to the power of M. In each of the following examples, Ge indicates germanium, and ZnS
e shows zinc selenide. The refractive indices of these materials are as follows.

[0016]

[Table 1] [Example 1] FNO = 1.2 f = 100 mm Surface number Radius of curvature Surface spacing Material Focal length 1 80.86203 7.24209 Ge 96.39099 Aperture: φ = 83.2 mm 2 104.63748 70.43518 3 0.00000 18.00000 ZnSe -332.46273 4 467.60884 12.44784 5 Image surface Second surface (aspheric surface) Conic constant k = 0.5140 Aspherical surface coefficient A4 = 6.70015 × 10−8, A6 = 3.999709 × 10−12 A8 = 4.79220 × 10−16, A10 = −1.76498 × 10−20 Four surfaces (aspherical surface) Conical constant k = 1.0000 Aspherical surface coefficient A4 = 1.16628 × 10−5, A6 = −3.80794 × 10−8 A8 = 4.335607 × 10−10, A10 = −1.48847 × 10−12

[0017]

Table 2 FNO = 1.2 f = 100 mm Surface number Curvature radius Surface spacing Material Focal length 1 80.87277 7.23695 Ge 96.45147 Aperture: φ = 83.2 mm 2 104.63769 71.46534 3 0.00000 16.13301 ZnSe -332.70378 4 467.94787 12.24049 5 Image surface (Aspherical surface) Conical constant k = 0.5163 Aspherical surface coefficient A4 = 6.73140 × 10−8, A6 = 3.990288 × 10−12 A8 = 5.94916 × 10−16, A10 = -4.47129 × 10−20 4th surface (aspherical surface) Conic constant k = 1.0000 Aspheric coefficient A4 = 1.18028 × 10−5, A6 = −3.257787 × 10−8, A8 = 3.79162 × 10−10, A10 = −1.31465 × 10−12

[0018]

Table 3 FNO = 1.2 f = 100 mm Surface number Radius of curvature Surface spacing Material Focal length 1 80.86086 7.22998 Ge 96.65311 Aperture: φ = 83.2 mm 2 104.53809 75.09480 3 0.00000 10.00000 ZnSe -326.23035 4 458.84299 11.29667 5 Image surface Second surface (Aspherical surface) Conic constant k = 0.5231 Aspherical surface coefficient A4 = 6.80298 x 10-8, A6 = 4.18990 x 10-12 A8 = 7.29610 x 10-16, A10 = -9.33235 x 10-20 Fourth surface (aspheric surface) Conic constant k = 1.0000 Aspheric coefficient A4 = 1.51001 × 10−5, A6 = −6.664819 × 10−8, A8 = 7.09024 × 10−10, A10 = −2.445163 × 10−12

[0019]

Table 4 FNO = 1.2 f = 100 mm Surface number Curvature radius Surface distance Material Focal length 1 80.83887 7.22531 Ge 96.81269 Aperture: φ = 83.2 mm 2 104.43512 77.51188 3 0.00000 6.00000 ZnSe -323.62660 4 455.18082 10.65457 5 Image surface Second surface (Aspherical surface) Conical constant k = 0.5284 Aspherical surface coefficient A4 = 6.887912 × 10−8, A6 = 3.41145 × 10−12 A8 = 1.59746 × 10−15, A10 = −3.26418 × 10−19 Fourth surface (aspherical surface) Conic constant k = 1.0000 Aspherical surface coefficient A4 = 1.85913 × 10−5, A6 = −1.16936 × 10−7 A8 = 1.24314 × 10−9, A10 = −4.38997 × 10−12 Tables 1 to 4 in FIGS. FIG. 10 shows various aberration diagrams of the first to fourth examples shown in Table 4. Here, FIGS. 5 to 8A are spherical aberration diagrams in the first to fourth examples, and FIGS.
FIGS. 5 to 8C show the astigmatism diagrams of the fourth embodiment.
FIGS. 5 to 8D show chromatic aberration of magnification in the first to fourth examples, and FIGS. 5 to 8E.
Is a coma aberration diagram at an angle of view ω = −4.45 in the first to fourth embodiments, and FIGS. 5 to 8F are a coma aberration diagrams at an angle of view ω = −3.38 in the first to fourth embodiments. , And FIGS.
FIGS. 5 to 8H show the angle of view ω in the first to fourth embodiments. FIGS.
= 0 is a lateral aberration diagram.

In each aberration diagram, FNO is the F-number, Y is the image height, ω is the angle of view, X is the aberration curve of 12 μm,
Y represents an aberration curve of 10 μm, and Z represents an aberration curve of 8 μm. In addition, in the astigmatism diagrams of FIGS. 5 to 8B, a broken line represents a meridional image plane, and a solid line represents a sagittal image plane. As is clear from the aberration diagrams of FIGS. 5 to 8, the infrared aspherical optical system according to each numerical example of the present invention can achieve excellent imaging performance despite its simple configuration. Is understood.

[0021]

As described above, according to the present invention, 7 to 13 μm
In an infrared imaging optical system using a wavelength band of about m,
Despite the extremely small number of components of two,
Good aberration correction can be achieved for the entire screen.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a lens according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a lens according to a third embodiment of the present invention.

FIG. 4 is a sectional view of a lens according to a fourth embodiment of the present invention.

FIG. 5 is a diagram illustrating various aberrations of the first example.

FIG. 6 is a diagram illustrating various aberrations of the second example.

FIG. 7 is a diagram illustrating various aberrations of the third example.

FIG. 8 is a diagram illustrating various aberrations of the fourth example.

[Explanation of symbols]

 L1 ‥‥ first lens L2 ‥‥ second lens S ‥‥ stop I ‥‥ image plane

Claims (2)

[Claims] 1. A positive meniscus lens comprising, in order from the object side, a spherical lens surface with a convex surface facing the object side and an aspherical lens surface with a concave surface facing the image surface side, and made of germanium. A lens surface on the object side is a flat surface, and a lens surface on the image side is an aspherical surface with a concave surface facing the image side;
And a plano-concave lens made of zinc selenide; and an aspheric optical system for infrared rays, characterized by satisfying the following conditions. (1) 0.955 <f1 / f <0.975 (2) -3.35 <f2 / f <-3.20 (3) 0.68 <d / f <0.80 (4) 0.065 <T1 / f <0.080 (5) 0.19 <t2 / f <0.05, where f: focal length of the entire infrared aspherical optical system, f1: focal length of the positive meniscus lens, f2: Focal length of the plano-concave lens, d: interval from the image side lens surface of the positive meniscus lens to the image side lens surface of the plano-concave lens, t1: axial thickness of the positive meniscus lens lens, t2: axis of the plano-concave lens Upper thickness. 2. The infrared aspherical optical system according to claim 1, wherein the following condition is satisfied. (6) 0.98 <TL / f <1.11 where TL is the distance (total length) from the object side lens surface of the positive meniscus lens to the image plane.