RU54215U1 - INFRARED LENS WITH FULLY VARIABLE FOCUS DISTANCE - Google Patents

Abstract

Usage: As a lens for a thermal imaging device with a continuously changing field of view. Purpose: Reducing the length of the lens and improving image quality over the entire range of the focal length. The essence of the utility model: In a lens with a smoothly varying focal length, containing a successively arranged stationary first component in the form of a positive convex-concave lens, a movable second component in the form of a negative biconcave lens, a movable third component in the form of a negative concave-convex lens, fixed fourth component in in the form of a positive concave-convex lens and the fifth component, consisting of the first positive convex-concave, the second negative convex-concave, the third from a negative lens, a fourth lens, and a fifth positive lens, in the fifth component, the third lens is biconcave, the fourth negative convex-concave, and the fifth biconvex, while the first surfaces of the third and fifth lenses of the fifth component are aspherical. Benefit: Reduced dimensions and improved image quality.

Description

The utility model relates to infrared optical systems and can be used in thermal imagers.

Known infrared lens with a smoothly changing focal length (see UK patent No. 1,532,096), containing sequentially arranged first stationary component consisting of one lens, a movable second component consisting of one lens, a movable third component consisting of one lens and fixed the fourth component, consisting of two lenses.

The disadvantage of this infrared lens is the small interval of the focal length (the ratio of the maximum focal length to the minimum M = 3.5), large dimensions (the length of the lens exceeds the maximum focal length by 1.3 times), and also a sufficiently large circle of aberration scattering from a point source radiation, which leads to blurring of the image and its poor quality.

Some of these shortcomings were eliminated in the infrared lens closest in technical essence to a continuously variable focal length (see US patent No. 6091551, M. class. G 02 B 15/14; G 02 B 13/14, publ. July 18, 2000. , the circuit in FIG. 21), containing a successive fixed component I with a focal length f1, consisting of a positive convex-concave silicon lens, a movable component II with a focal length f2, consisting of a negative biconcave silicon lens, a movable component III with a focal length distance f3, consisting from a negative concave-convex lens from Germany, then the stationary components IV with a focal length f4, consisting of a positive concave-convex lens from silicon and a component V with a focal length f5, consisting of the first positive convex-concave lens from silicon, the second negative convex a concave lens of germanium, a third negative concave-convex lens of silicon, a fourth positive concave-convex lens of silicon, and a fifth positive

convex-concave silicon lens.

The ratio of the maximum focal length to the minimum in this infrared lens reaches M = 4. Image quality is ensured by the ratio of the focal lengths of the components with the maximum focal length of the lens ft: 1.00 <f1 / ft, - 0.40> f2 / ft and 0.35 <f5 / ft <0.70 (see also Shpyakin MG “Research and calculation of lenses with wide intervals of changing the focal length ”, abstract of the dissertation for the degree of candidate of technical sciences, L. 1971, p.13), which presents a series of equations linking the optical forces of components, analyzing which you can get the required ratio of focal lengths: f1 / ft> 1, f2 / ft <0, etc. The focal length of the lens shown in Fig.21 US patent No. 6091551, varies in the range from 50 mm to 200 mm When scaling design parameters, for example, to obtain a variable focal length from 75 mm to 300 mm, the lens length becomes unacceptable for use in thermal imaging equipment (the lens length exceeds the maximum focal length by 1.87 times), and its aberration characteristics deteriorate proportionally scale.

Thus, the disadvantage of the described infrared lens is the large size with insufficient image quality.

The problem the utility model is aimed at reducing the length of the infrared lens relative to its maximum focal length while maintaining the ratio of the maximum focal length to the minimum, as well as increasing the energy concentration in a given scattering circle.

This goal is achieved by the fact that in an infrared lens with a smoothly changing focal length, containing sequentially located a stationary first component in the form of a positive convex-concave lens, a movable second component in the form of a negative biconcave lens, a movable third component in the form of a negative concave-convex lens, motionless the fourth component in the form of a positive concave-convex lens and the fifth component, consisting of the first

positive convex-concave, second negative convex-concave, third negative lens, fourth lens and fifth positive lens, characterized in that in the fifth component, the third lens is biconcave, the fourth is negative convex-concave, and the fifth is biconvex,

And also by the fact that the first surfaces of the third and fifth lenses of the fifth component are aspherical.

The aspherical surface of the third lens of the fifth component is made in accordance with the equation

y ² + z ² = -2rx + (0.165627 ... 0.165632) rx ² , where

y is the axis of the coordinate system lying in the plane of the meridional section of the lens;

z is the axis of the coordinate system lying in the plane of the sagittal section of the lens;

x is the axis of the coordinate system coinciding with the optical axis of the lens;

r is the radius of curvature of the initial sphere of the mentioned surface of the third lens of the fifth component.

The aspherical surface of the fifth lens of the fifth component is made in accordance with the equation

y ² + z ² = 2rx + 0.1853rx ² , where

y is the axis of the coordinate system lying in the plane of the meridional section of the lens;

z is the axis of the coordinate system lying in the plane of the sagittal section of the lens;

x is the axis of the coordinate system coinciding with the optical axis of the lens;

r is the radius of curvature of the initial sphere of the mentioned surface of the fifth lens of the fifth component.

The drawing shows an optical diagram of an infrared lens with a continuously variable focal length with the location of the components for the focal length of 300 mm

The lens contains a fixed first component I sequentially located along the optical axis in the form of a positive convex-concave

lens 1, the movable second component II in the form of a negative biconcave lens 2, the movable third component III in the form of a negative concave-convex lens 3, the stationary fourth component IV in the form of a positive concave-convex lens 4 and the stationary fifth component V, consisting of the first positive convex -concave lens 5, the second negative convex-concave lens 6, the third negative biconcave lens 7, the fourth negative convex-concave lens 8 and the fifth positive biconvex lens 9. The first surfaces are third 7 minutes and 9 of the fifth lens formed of the fifth component V aspherical.

The aspherical surface of the third lens 7 of the fifth component V can be made in accordance with the equation

y ² + z ² = -2rx + (0.165627 ... 0.165632) rx ² , where

y is the axis of the coordinate system lying in the plane of the meridional section of the lens;

z is the axis of the coordinate system lying in the plane of the sagittal section of the lens;

x is the axis of the coordinate system coinciding with the optical axis of the lens;

r is the radius of curvature of the initial sphere of the mentioned surface of the third lens 7 of the fifth component.

The aspherical surface of the fifth lens 9 of the fifth component V can be made in accordance with the equation

y ² + z ² = 2rx + 0.1853rx ² , where

y is the axis of the coordinate system lying in the plane of the meridional section of the lens;

z is the axis of the coordinate system lying in the plane of the sagittal section of the lens;

x is the axis of the coordinate system coinciding with the optical axis of the lens;

r is the radius of curvature of the initial sphere of the mentioned surface of the fifth lens 9 of the fifth component.

The design parameters of the inventive infrared lens with a smoothly changing focal length from 75 mm to 300 mm for the spectral region 3.0-5.0 μm are presented in table 1.

Table 1 Component No. Lens number The value of the radius of the spherical surface, mm Axial thickness, mm Material I one r1 = 410.2
r2 = 889.2 d1 = 12 Silicon d2 = 9 II 2 r3 = -8318.0
r4 = 370.7 d3 = 6 Silicon d4 = 109.3 III 3 r5 = -212.3
r6 = -381.9 d5 = 6 Germanium d6 = 55.8 IV four r7 = -261.8
r8 = -166.72 d7 = 6 Silicon d8 = 6 V 5 r9 = 114.82
r10 = 287.1 d9 = 7 Silicon d10 = 5 6 r11 = 357.3
r12 = 189.23 d11 = 6 Germanium D12 = 85 7 r13 = -150,2097 ^*)
rl4 = 127.35 d14 = 4 Silicon D15 = 3 8 r15 = 760.3
r16 = 580.8 d16 = 5 Silicon d17 = 1 9 rl7 = 160,1089 ^**)
r18 = 128.53 D18 = 5 Silicon A \ ^ O ^
^*) Aspherical surface of type ² + х ² = -300,419х + 24,879х
^**) Aspherical surface of type ² + x ² = 320.218x + 29.668x

Changing the focal length of the lens is done by moving components II and III. The values of the variable air gaps d2, d4 and d6 for the three values of the focal lengths of the lens are shown in table 2.

table 2 Focal distance d2 mm d4 mm d6 mm lens mm 300 157.0 11.6 5.5 149,878 96.1 31.6 46,4 75 9.0 109.3 55.8

The table shows that the ratio of the maximum value of the focal length to the minimum M = 4.

With the claimed design, the lens length is 376.15 mm and does not exceed the maximum focal length by more than 1.25 times.

The front surfaces of the third 7 and fifth 9 lenses of the fifth component V are aspherical to improve image quality, characterized, for example, by a higher concentration of energy in the spot of a given diameter. Table 3 shows the values of the energy concentration in a spot with a diameter of 30 μm for the three values of the focal lengths of the inventive lens and the lens taken as a prototype, obtained by calculation.

Table 3 Parameter The inventive lens Prototype lens Focal distance, 75 150 300 fifty one hundred 200 mm Concentration energy% 87 85 83 58 73 83

Thus, the implementation of an infrared lens with a smoothly changing focal length in accordance with the formula of the claimed materials allows for smaller dimensions with higher image quality than in the known designs of similar lenses.

Claims (4)

1. An infrared lens with a smoothly varying focal length, comprising successively arranged stationary first component in the form of a positive convex-concave lens, a movable second component in the form of a negative biconcave lens, a movable third component in the form of a negative concave-convex lens, and a motionless fourth component in the form of a positive concave-convex lens and the fifth component, consisting of the first positive convex-concave, the second negative convex-concave, the third negative Inz, the fourth lens and the fifth positive lens, characterized in that in the fifth component the third lens is biconcave, the fourth negative convex-concave, and the fifth biconvex. 2. The infrared lens according to claim 1, characterized in that the first surfaces of the third and fifth lenses of the fifth component are aspherical. 3. The infrared lens according to claim 1 or 2, characterized in that the aspherical surface of the third lens of the fifth component is made in accordance with the equation y ² + z ² = -2rx + (0.165627 ... 0.165632) rx ² , where y is the axis of the coordinate system lying in the plane of the meridional section of the infrared lens; z is the axis of the coordinate system lying in the plane of the sagittal section of the infrared lens; x is the axis of the coordinate system that coincides with the optical axis of the infrared lens; r is the radius of curvature of the initial sphere of the mentioned surface of the third lens of the fifth component. 4. The infrared lens according to any one of claims 1 to 3, characterized in that the aspherical surface of the fifth lens of the fifth component is made in accordance with the equation y ² + z ² = 2rx + 0.1853rx ² , where y is the axis of the coordinate system lying in the plane of the meridional section of the infrared lens; z is the axis of the coordinate system lying in the plane of the sagittal section of the infrared lens; x is the axis of the coordinate system that coincides with the optical axis of the infrared lens; r is the radius of curvature of the initial sphere of the mentioned surface of the fifth lens of the fifth component.