JPS62109014A - Lens for infrared ray - Google Patents

Abstract

PURPOSE:To provide the performance equiv. to the performance in the central part of a lens up to the peripheral part while having a half angle of view as large as about 20 deg. and about -1% distortion aberration by providing the 1st, 2nd, and 3rd lenses successively from an object side to said lens, using germanium to form the respective lens and constituting the lens in such a manner as to satisfy specific conditions. CONSTITUTION:This lens for IR rays of 3-group 3-element constitution is arranged with the 1st, 2nd, and 3rd lenses successively from the object side and satisfies the conditions expressed by the formulas (I)-(III) when the distances between the lens faces are designated as d1-d5 successively from the object side, the radii of curvature of the respective lens faces on the object side of the 1st, 2nd, and 3rd lenses as r1, r3, r5, and the combined focal length of the entire system is designated as f. The respective lenses are made of germanium. For example, the left side of the figure is the object side and this lens is constituted of the 1st lens (convex meniscus lens) 10A, 2nd lens (concave meniscus lens) 12A and 3rd lens (convex meniscus lens) 14A.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an infrared lens, and more particularly to an infrared lens composed of three elements in three groups.

(Prior art) A triplet-type infrared lens consisting of 3 elements in 3 groups with a half angle of view of about 20 degrees was conventionally disclosed in Japanese Patent Application Laid-Open No.
One disclosed in Japanese Patent No. 31444 is known. This conventionally known infrared lens has a large half angle of view of 22.5 degrees, but if you try to improve the performance, the distortion will be negative and will be as large as about 4%, and the distortion ≦ recovery difference will be about negative 1%. However, there was one problem in that peripheral performance deteriorated.

(Purpose) The present invention was made in view of the above-mentioned circumstances, and its purpose is to target infrared rays with a wavelength of around 10 μm, have a large half-field angle of about 20 degrees, and reduce distortion. Although the aberration is about 11%.

To provide an infrared lens that has the same performance up to the periphery as the center.

(composition) The present invention will be explained below.

The infrared lens of the present invention is composed of three lenses in three groups, and the first, first and second lenses are arranged in order from the object side. Second. It is made by arranging the third lens. These three lenses are made of germanium.

The third lens and the third lens are convex meniscus lenses, and both are arranged with their convex surfaces facing the object side. A second lens provided between the third lens and the third lens.
The lens is a concave meniscus lens 1, and is arranged so that its concave surface faces the object side.

The distance between the lens surfaces is set sequentially from the object side to d1, d2. d
3°d4. For example, dl is the distance on the optical axis between the object side lens surface of the first lens and the image side lens surface, and d2 is the distance between the image side lens surface of the second lens and the object side lens of the second lens. This is the distance on the optical axis between the two surfaces. Further, the radius of curvature of the object-side lens surface of the second lens is r1, the radius of curvature of the object-side lens surface of the second lens is r3, and the radius of curvature of the object-side lens surface of the third lens is r5. 1st. Second. The radius of curvature of each lens surface on the image side of the third lens is r2. r
4. It is r6.

Now, in the present invention, the above d1 to d5. rl.

r3. r5 satisfies the following three conditions.

(I) 1.79f<dl+d2+d3+d4+d
5<1.89f(I1) 0.63<d2/d
4 <0.77rl+r5 (In) -2,72<-<-2,63 Note that f is the composite focal pressure of the entire system.

In triplet-type lenses made of germanium, it is necessary to reduce the Petzval sum as the angle of view increases, and when the half angle of view is about 20 degrees,
A Petzval sum of 0.21 is appropriate. To achieve this, the total length of the lens system must be long to a certain extent.6 Conditions (1) define the range of this total length;
When the upper limit is exceeded, one angle of view becomes narrower, the meridional value becomes negative, and the astigmatic difference from the sagittal value increases. Moreover, when the lower limit is exceeded, the curvature of field becomes large and the performance in the peripheral area deteriorates.

As can be seen from condition (I), the infrared lens of the present invention has a longer overall length of the lens system than conventional lenses.

Next, condition (■) is mainly for correcting distortion aberration, and it is desirable that d2/d4 be close to 1.
If this becomes larger than the upper limit of 0.77, the distortion itself becomes smaller, but the image plane becomes negative. Furthermore, when the lower limit of 0.63 is exceeded, the distortion becomes greater than 11%.

Condition (In), along with conditions CI) and (II), is for making the image plane positive.

If the lower limit is exceeded, the image plane will not be positive; if the upper limit is exceeded,
Too positive. Therefore, 1 condition (III) is condition (I
), (n), this can be said to be a condition for keeping the image plane within an appropriate positive range.

Note that the infrared lens of the present invention targets far infrared rays with a wavelength of around 10 μm.

Hereinafter, description will be given based on specific examples.

In addition, in each example and the corresponding drawing, F:F
Number f: Synthetic focal length of the lens system ω: Half angle of view ni: Refractive index (for a wavelength of I0 μm) Σp: Indicates the sum of pesotubars.

Moreover, rl to r6 are the radius of curvature of the lens surface of each lens, and dl to d5 are the distances between the lens surfaces.

Furthermore, in the three embodiments listed below, all have an aperture between the first lens and the second lens, and the second lens surface (the image side lens surface of the second lens) and the aperture surface The distance between the two is dg. Further, the radius of curvature of the window glass surface of the vidicon or detector using the infrared lens of the present invention is set to r7. r8 -0 (Example 1) ゛Figure 1 shows Example 1. The left side of the figure is the object side, and 10A is the first lens (convex meniscus lens);
Reference numeral 12A indicates a second lens (concave meniscus lens), and reference numeral 14A indicates a third lens (convex meniscus lens). Further, reference numeral 11 indicates a diaphragm, and reference numeral 15 indicates a window glass of a vidicon or detector.

The specific values are as follows.

and others (Example 2) FIG. 4 shows Example 2. Code 10B.

12B and 14B are rod 1. Second. The third lens, reference numeral 11, is an aperture, and reference numeral 15 is a window glass.

The specific numbers are as follows.

Fo, 8. f = 100.01, ω = 19.8°,
tedi=185i=1 (Example 3) Example 3 is shown in FIG. Code 10C, 12C, L4C
are respectively the first. Second. In the third lens, reference numeral 11 indicates an aperture, and reference numeral 15 indicates a window glass. The specific numbers are as follows.

Fo, 8. f=100. OO,ω=19. g°
Two elements di=188.2·i=1 Aberration diagrams are shown in FIGS. 2, 3, 5, 6, 8, and 9. FIG. 2, FIG. 5, and FIG. 8 are aberration curve diagrams, and FIG. 3, FIG. 6, and FIG. 9 are lateral aberration curve diagrams. In the figure.

SA: Spherical aberration (solid line) SC: Sine condition (dashed line) DIST: Distortion aberration COM^: Lateral aberration It is.

FIG. 2 is an aberration diagram of Example 1, and FIG. 3 is Example 1.
FIG. 3 is a lateral aberration curve diagram.

5 and 6 are an aberration curve diagram and a lateral aberration curve diagram regarding Example 2. FIG.

8 and 9 are aberration curve diagrams for Example 3, horizontal
It is an aberration curve diagram.

As is clear from these aberration diagrams, in each example,
Although the distortion aberration is as small as 11%, all aberrations are well corrected.

Here, in each embodiment, the aperture 11 disposed between the first lens and the second lens will be described. This aperture 11 has the effect of reducing distortion.

Note that the surface pressure fid6 between the second surface of the third lens and the object-side surface of the window glass may be any value, and this value may be changed from the value in the example.

The performance of each example remains unchanged.

(Effects) According to the first aspect of the present invention, a novel infrared lens can be provided. Since this infrared lens is constructed as described above, the half angle is as large as approximately 20 degrees, and the distortion is 11%.
Even though the performance is about the same as that of the central part, it has the same performance up to one periphery.

The infrared lens of the present invention can be used in industrial and medical thermography devices, and is particularly suitable for φ1818C vidicon.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing one embodiment of the present invention, FIGS. 2 and 3 are aberration diagrams regarding the above embodiment, and FIG. 4 is a diagram showing another embodiment of the present invention. , FIG. 5 and FIG. 6 are aberration diagrams regarding the above-mentioned another embodiment, and FIG. 7 is a diagram showing another embodiment of the present invention.
FIGS. 8 and 9 are aberration diagrams regarding the other embodiments described above.

10A, IOB, IOc... No. 12A, 1
2B, 12C...Second lens, 14A, 14B, 1
4C...Third lens.

杢Z phantom SA, SCOS, DM DIST θHA Fo, 3 1t/lf, 1' u/
4'll.

COMA FOJ utl'll' ut/
'? , 1739 shares OMA

Claims (1)

[Claims] First, second, and third lenses are arranged in order from the object side, the first lens being a convex meniscus lens with its convex surface facing the object side, and the second lens having a concave surface facing the object side. The third lens is a convex meniscus lens with the convex surface facing the object side, and the distance between the lens surfaces is set sequentially from the object side to d1, d2, d3, d.
4, d5, the radius of curvature of each lens surface on the object side of the first, second, and third lenses is r1, r3, r5, and the composite focal length of the entire system is f, (I) 1.79f<d1+d2+d3+d4+d5<
1.89f (II) 0.63<d2/d4<0.77 (III)-2.72<(r1+r5)/r3<-2.6
An infrared lens composed of three elements in three groups, which satisfies the following three conditions and is characterized in that the material of each lens is germanium.