JP2002196233A - Infrared optical system and infrared optical device provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fast infrared optical lens system or the like which has small number of elements and a large back focus, and various aberrations including a distortion aberration are excellently compensated. SOLUTION: The system is composed of a first lens group G1 which has a negative refraction power including at least a negative meniscus lens L11 of which convex surface is directed to an object and a second lens group G2 which has a positive refraction power, which are arranged from the side of the object, and formula of predetermined conditions are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared optical system,
The present invention relates to an infrared optical system suitable for an infrared imaging device and the like.

[0002]

2. Description of the Related Art In recent years, various infrared optical systems have been proposed with the development of CCDs (charge coupled devices), which are area detectors, as infrared detectors.

However, in comparison with the optical system usually used in the visible region, in the infrared wavelength region, there are problems such as the sensitivity and light quantity of the CCD. 1.2) is generally used.

In the infrared wavelength region, unnecessary infrared rays radiated from other than the object, such as self-radiation of the lens barrel, are generated. An aperture is placed behind the optical system (image side) so that the unnecessary infrared rays do not enter the detector. In many cases, the aperture is matched with a material (cold shield) cooled so as not to reflect or transmit infrared rays, thereby achieving aperture matching. Because of this configuration, it is difficult to design a wide-angle lens that favorably corrects distortion.

[0005] Optical materials used in infrared optical systems are more expensive than visible optical materials. Therefore,
It is desirable that the number of lenses constituting the infrared optical system be small in terms of cost.

As a wide-angle infrared lens with aperture matching, for example, those disclosed in JP-A-4-356008 and JP-A-7-318797 are known.

[0007]

Problems to be Solved by the Invention
The lens system disclosed in Japanese Patent Application Laid-Open No. 8 (1996) -1995 has a configuration in which an intermediate image is formed and the intermediate image is relayed by a relay lens.
For this reason, the number of constituent lenses is large. Therefore, the transmittance decreases and the S / N ratio deteriorates. In addition, flare is also likely to increase, which is disadvantageous in performance. Further, as described above, there is a problem that the optical material for the infrared optical system is expensive and disadvantageous in cost.

The lens system disclosed in JP-A-7-318797 has a large aperture ratio of F / 2, which is large and dark. In addition, since the back focus is increased, the power of the first lens group is increased, and there is a problem that distortion is increased.

The present invention has been made in view of the above-mentioned problems, and has a small number of lenses, a large back focus, and a bright infrared optical system and infrared optical system in which various aberrations including distortion are satisfactorily corrected. It is intended to provide a device.

[0010]

In order to solve the above problems, the present invention provides, in order from the object side, at least one negative meniscus lens L11 having a convex surface facing the object side. The first lens unit G2 includes a lens group G1 and a second lens group G2 having a positive refractive power.
And an infrared optical system characterized by satisfying the following.

-6 <f1 / f <-4 (1) where, f: focal length of the entire infrared optical system, f1: focal length of the first lens group G1. Conditional expression (1) defines an appropriate range of the ratio between the focal length of the first lens group G1 and the focal length of the entire system. When the value exceeds the upper limit of conditional expression (1), distortion increases. Conversely, when the value goes below the lower limit of conditional expression (1), the back focus becomes short. In any case, the above object cannot be achieved.

In a preferred aspect of the present invention, it is preferable that one surface of the negative meniscus lens of the first lens group G1 is aspheric.

In a preferred aspect of the present invention, it is desirable that the second lens group G2 includes a lens L21 having an aspheric surface 3.

According to the present invention, there is provided an infrared optical system according to any one of claims 1 to 3, and an infrared detecting unit P for receiving infrared light from an object by the infrared optical system. An infrared optical device is provided.

In the section of the means for solving the above-mentioned problems, which explains the configuration of the present invention, the drawings of the embodiments of the present invention are used to make the present invention easy to understand. However, the present invention is not limited to this.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) FIG. 1 is a configuration diagram of an infrared imaging apparatus having an infrared optical system according to the present embodiment. In order from the object side, the first lens group G1 includes one negative meniscus lens L11, and the second lens group G2 includes three lenses L21, L22, and L23 having positive, negative, and positive refractive power. Is done. And the CCD window D
2 is provided. Detector P
Is a dual member C having a dual window D1 and an aperture stop S.
Covered with. The interior of the dual member C is cooled by a cooler (not shown). By performing the above-described aperture matching, unnecessary infrared radiation from a lens barrel or the like can be shielded.

The infrared optical system suppresses the power of the first lens group G1 by satisfying conditional expression (1). As a result, a long back focus is secured.

In this embodiment, the surfaces 1 and 3 are aspherical. As a result, distortion is more effectively corrected.

Table 1 shows the specification values of the present embodiment. still,
The aspherical shape in the specification table is represented by the following equation.

[Number 1] ^{Z = (Y 2 / R)} / [1+ [1- (1 + K) Y 2 / R 2] 1/2] + AY 4 + B
Y ⁶ + CY ⁸ + DY ¹⁰

Here, Y represents the distance from the optical axis, and Z is the displacement (sag amount) from the reference plane perpendicular to the optical axis to the aspherical surface, including the intersection of the optical axis and the aspherical surface. R is a paraxial radius of curvature of the aspheric surface, K is a conic coefficient, and A to D are aspheric surface coefficients. “E−n” in the aspherical surface coefficient is “× 1”.
0 ^-n ". Hereinafter, the same applies to all embodiments.

The unit of the focal length, the radius of curvature, the distance between surfaces, and other lengths in the specification table are generally "mm".
The optical system is not limited to this, since the same optical performance can be obtained even if the optical system is enlarged or reduced proportionally.

[0023]

[Table 1] (Overall specifications) Focal length f = 7.6 mm F-number F / 1.2 Angle of view 2ω = 66 ° (Lens data) Surface radius of curvature Surface spacing Optical material Refractive index Abbe number 1 30.27558 2.000000 Si 3.425406 240.95 2 21.68816 90.619207 3 130.39238 3.000000 Si 3.425406 240.95 4 22600.38571 22.227521 5 45.18173 1.500000 Ge 4.024610 102.22 6 27.87542 1.232130 7 32.04095 4.000000 Si 3.425406 240.95 8 -4229.22605 5.621142 9 ∞ (plane) 3.000000 Si 3.425406 240.95 10∞ (plane) 1.260000 110000 ∞ (plane) 0.300000 Si 3.425406 240.95 (aspheric coefficient) [Surface 1] K = 0.280716 A = -0.132491E-06 B = 0.497655E-09 C = -0.697027E-12 D = 0.521752E-15 [Surface 3] K = 0.000000 A = -0.184407E-05 B = -0.783308E-09 C = -0.322286E-12 D = 0.0 (Value corresponding to conditional expression) f1 = -37.75 f1 / f = -4.97

In the optical material, Si indicates silicon, and Ge indicates germanium. The refractive index in Table 1 is wavelength 4μ
m and the Abbe number is (n4-1) /
(N3-n5). Here, n3, n4, and n5 are refractive indexes at wavelengths of 3 μm, 4 μm, and 5 μm, respectively.

Table 2 shows the refractive indices n3, n4 and n5.

[0026]

[Table 2] Optical material n3 n4 n5 Si 3.432338 3.425406 3.422272 Ge 4.044976 4.024610 4.015388

FIG. 2 shows various aberration diagrams of the present embodiment. FIG.
The dotted line in the middle represents the sagittal image plane, and the solid line represents the meridional image plane. It can be seen from FIG. 2 that various aberrations are satisfactorily corrected. The distortion at the maximum angle of view is -4.5%.

(Second Embodiment) FIG. 3 is a configuration diagram of an infrared imaging apparatus having an infrared optical system according to the present embodiment.
Note that the same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description will be omitted.

The infrared optical system according to the present embodiment has, in order from the object side, a first lens group G1 including one negative meniscus lens L11 and four positive, negative, negative, and positive refractive powers. A second lens group G2 including lenses L21, L22, L23, and L24.

In the present embodiment, the surface 1 is made aspherical, and distortion is more effectively corrected.

Table 3 shows the specification values of the second embodiment.

[0032]

[Table 3] (Overall specifications) Focal length f = 7.6 mm F-number F / 1.2 Angle of view 2ω = 66 ° (Lens data) Surface radius of curvature Surface spacing Optical material Refractive index Abbe number 1 36.20205 2.000000 Si 3.425406 240.95 2 24.87787 109.348762 3 94.04404 6.000000 Si 3.425406 240.95 4 -574.24433 8.896893 5 -60.83181 2.000000 Ge 4.024610 102.22 6 -122.38193 25.095198 7 24.75313 1.500000 Ge 4.024610 102.22 8 21.20958 1.859147 9 28.30978 3.500000 Si 3.425406 240.95 10 88.24014 5.000000 11 95 24012.400 (Plane) 1.260000 13 ∞ (Plane) 10.240000 14 ∞ (Plane) 0.300000 Si 3.425406 240.95 (Aspherical coefficient) [Surface 1] K = -0.128160 A = 0.836588E-06 B = 0.412366E-08 C = -0.530485E- 11 D = 0.642836E-14 (Values corresponding to conditional expressions) f1 = -37.48 f1 / f = -4.93

FIG. 4 shows various aberration diagrams of the present embodiment. FIG.
The dotted line in the middle represents the sagittal image plane, and the solid line represents the meridional image plane. It can be seen from FIG. 4 that the various aberrations are well corrected. The distortion at the maximum angle of view is -4.5%.

[0034]

As described above, according to the present invention,
It is possible to provide a bright infrared optical system and an infrared optical device in which the number of lenses is small, the back focus is large, and various aberrations including distortion are satisfactorily corrected.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an infrared imaging device including an infrared optical system according to a first embodiment.

FIG. 2 is a diagram illustrating various aberrations of the infrared optical system according to the first embodiment.

FIG. 3 is a configuration diagram of an infrared imaging device including an infrared optical system according to a second embodiment.

FIG. 4 is a diagram illustrating various aberrations of the infrared optical system according to the second embodiment.

[Explanation of symbols]

 G1 First lens group G2 Second lens group S Aperture (cold shield) D1 Dual window D2 CCD window P Infrared detector C Dual member

Claims (4)

[Claims] 1. A first lens group having a negative refractive power including at least one negative meniscus lens having a convex surface facing the object side, and a second lens group having a positive refractive power, in order from the object side. An infrared optical system which is constituted and satisfies the following conditional expressions. −6 <f1 / f <−4, where f: focal length of the entire infrared optical system, f1: focal length of the first lens group. 2. The infrared optical system according to claim 1, wherein one side of the negative meniscus lens of said first lens group is aspheric. 3. The infrared optical system according to claim 1, wherein said second lens group has an aspherical lens. 4. An infrared optical system according to claim 1, further comprising: an infrared detector that receives infrared light from an object by the infrared optical system. Infrared optical device.