JPS625211A - Lens for infrared rays - Google Patents

Abstract

PURPOSE:To obtain the lens which is small, light and has high performance by composing so that the balance of the center and the periphery of the screen can be good, the distortion aberration can be within 1% and the aperture efficiency can be kept to 100% up to the periphery of the screen. CONSTITUTION:The germanium of three groups three sheets is used which is composed of the first lens of the convex meniscus to turn to convex surface to the object side in the sequence from the object side, the second lens of the concave meniscus to turn the concave surface to the object side and the third lens of the convex meniscus to turn the convex surface to the object side. Respective conditions of formulas I-III should be satisfied. Provided that the radius of curvature to be turned to the object side of the third lens is gamma5, the interval between the first lens and the second lens is d2, the interval between the second lens and the third lens is d4, the composite focus distance between the first lens and the second lens is f1.2 and the composite focus distance of all systems is (f). When respective lenses are thin lenses, the Petzval sum comes to be large, and it is corrected that the image surface falls to the negative side. The balance of the spherical aberration and the image surface is formed, and the distortion aberration is corrected. Further, the basic value to determine the lens concerning the refracting power from the first lens to the second lens is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (II Industrial Field of Application) This invention relates to an infrared lens, particularly a compact far-infrared lens.

(Prior art) Detectors, vidicon, etc. used for far infrared rays with a wavelength of around 10 μm have low sensitivity, and in addition, germanium used as a material for imaging lenses has lower transmittance than optical glass and has a large aperture. It is desirable that the lens be constructed with a thin lens. Furthermore, since the refractive index is high and the surface reflection is large, the number of constituent elements is also required to be small.

As such an imaging lens for infrared light with a wavelength of around 10 μm, there are a first lens with a convex meniscus with the convex surface facing the object side, a second lens with a concave meniscus with the concave surface facing the object side, and a convex lens with the convex surface facing the object side. A lens system using germanium is known that has a three-element structure in three groups, including a convex meniscus third lens with the lens facing the object side. Of these, British Patent No. 134
No. 5505 was the first lens of this type, but it had the problem of a large curvature of field. Japanese Patent Application Publication No. 5
The one with No. 2-37444 has a wide angle of view and is the next one,
Since the front aperture is used, if you try to improve the imaging performance, the distortion will become large and negative. The lens disclosed in JP-A No. 52-85834 is intended for telephoto viewing and has a half angle of view of 4.6, but the perapal sum is about 0.4, making it difficult to increase the angle of view. The lens disclosed in Japanese Patent Application Laid-Open No. 52-86344 has a medium angle of view, but has a thick composite lens, a long overall length, and a front diaphragm, resulting in asymmetrical comatic aberration. Japanese Unexamined Patent Publication No. 57-
The one in No. 200010 also has a medium viewing angle tube, but the curvature of field is large. This is due to the small size of the combined focal length of the first and second lenses, t'' f4,2%, and the combined focal length of the entire system, m'kf, of 9 and *,'/71.2, 0.362. .

(Problems to be Solved by the Invention) This invention uses a relatively thin lens, and although the overall length is short and compact, the aperture efficiency is maintained at 100 inches to the periphery, and the half-field brightness is approximately 10 inches. The objective is to obtain an infrared lens that has good performance and is suitable for use in, for example, a φ18100 vidicon.

Structure of the Invention (Means for Solving Problems) The structure of the lens of this invention is shown in FIGS. 1 and 4.
As shown in the figure, from the object side, the first lens is a convex meniscus with its convex surface facing the object side, the second lens is a concave meniscus with its concave surface facing the object side, and the second lens is a convex meniscus with its convex surface facing the object 111. Using germanium with 3 elements in 3 groups and 9 lenses, the curvature of the third lens toward the object side is half 1 t '3, the distance between the first lenses is d2,
The distance between the second lens and the third lens is d4% and the distance between the first lens and @
When the combined focal length of the two lenses is f1.2 and the combined focal length of the entire system is f, 0.6Of<rs<0.
75f...Tune (1) 1.2 gu2/d, <
1.4 ・・・・・・Mackerel) 0=6 <
f/f1.2<0.7 (3
) satisfies each condition.

(Function) When each lens is a thin lens, the purpose of the PP(t) is to correct the inclination of the edge surface to the negative side when the perapal sum is large. It is necessary to

If the lower limit is exceeded, the surface becomes excessively positive and the astigmatism difference becomes large. If the upper limit is exceeded, Meridional Tsumen will be busy 9,
Performance decreases.

The strip FF (2) balances spherical aberration and field curvature.
, is for correcting distortion aberration; when the lower limit is exceeded, the spherical aberration becomes negative and the curvature of field becomes positive, and especially when the germ height is positive, the comatic aberration of light rays with a low incident height becomes large9, Distortion becomes too positive. When the upper limit is exceeded, the meridional iron surface in particular becomes negative, resulting in poor balance with spherical aberration.

Condition (3) relates to the refractive power from the first lens to the second lens, and is a basic directness that determines the lens configuration.If the lower limit is exceeded, the astigmatism difference will become large at large angles, and if the upper limit is exceeded, the astigmatism difference will be large. Comatic aberration in the angle of view causes a difference in distance between the sagittal image plane and the meridional image plane.

Ninth, the diaphragm 9 is an effect tube that improves the symmetry of comatic aberration by making the effective diameter of the first lens as small as possible by making the effective diameter of the first lens as small as possible.

(Example) Examples of the present invention will be shown below. The symbols in the table have the following meanings.

F: F number f: Synthetic focal length of lens system ω: Half angle of view r: Radius of curvature of lens surface d: Distance between lens surfaces n: Refractive index of lens material (germanium) at wavelength 10P1 ds: From second surface to aperture Distance to surface r7, s: Vidicon or detector window glass surface: 1st
Distance from surface to 6th surface Example I Fo, 9 f=100 ω=10.2°d2/f
1. == 1.357'/f1.2=O-625
'a ''24 L=124.2 Example 2 Fo, 9 f=100 ω=10.2°d2/a
4= 1.236 f/f1@2= 0.654d3
=26.2 L=126.2 Example 3 Fo, 9 f=100 ω=10.2°d2/
a4= 1.244 f/f1@2= 0.662d
, =28.6 L=126.6 The distance d6 between the window glass and the infrared lens described above may be arbitrarily changed for purposes such as focusing, and has little effect on imaging performance.

Effects of the Invention The infrared lens of the present invention has a good balance between the screen center and the periphery, distortion aberration is within 1%, and low screen peripheral salt and aperture efficiency, as seen in the above embodiments and their aberration curve diagrams. remains at 100*. In this way, the lens of the present invention can be made into a high-performance infrared lens that is small and lightweight.

[Brief explanation of drawings]

@ Figures 1, 2, and 3 are cross-sectional views, aberration curve diagrams, lateral aberration curve diagrams, and Figures 4 and 5 of Example 1 of the lens system of the present invention.
Figure 6 is a cross-sectional view, aberration curve diagram, and transverse aberration curve diagram of Example 2, and Figures 7, 8, and @9 are a cross-sectional diagram, aberration curve diagram, and transverse aberration curve diagram of Example 3. Each is shown below. Figure 1 Figure 2 F O,9ω=10.2° W=10.2° Spherical aberration sine condition Astigmatism Distortion Figure 3 'IjL4 Figure! E 7 Figure 5 Spherical 2 difference Astigmatism Distortion aberration sine condition Figure 6 Figure 8 FO99 = 10.2 ω = 10.2 Sphere 1” difference Astigmatism φ curvature aberration sine condition Figure 9

Claims (1)

[Claims] In order from the object side, a first convex meniscus lens with a convex surface facing the object side, a second concave meniscus lens with a concave surface facing the object side, and a third convex meniscus lens with a convex surface facing the object side. It is composed of three lenses in three groups, and the radius of curvature of the third lens toward the object side is r_3, the distance between the first lens and the second lens is d_2, and the distance between the second lens and the third lens is d_4.
, the combined focal length of the first lens and the second lens is f_1_.
_2, when the combined focal length of the entire system is f, 0.60f<r_5<0.75f 1.2<d_2/d_4<1.4 0.6<f/f_1_. An infrared lens that satisfies the following conditions: ＿2<0.7