RU55155U1 - 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: Increasing the interval of changing the focal length, decreasing the length of the lens and improving the image quality throughout the entire interval of changing the focal length.

The essence of the utility model: In a lens with a smoothly varying focal length, consisting of a successively arranged stationary first component containing a positive convex-concave lens, mounted to move along the optical axis the movable second component containing a negative convex-concave lens, and a third component, made in the form of a negative concave-convex lens, stationary fourth component, made in the form of a positive concave-convex lens, and the fifth to mponenta comprising first and second concave-convex positive lens, the first component is additionally introduced second negative convex-concave, biconcave negative third, fourth and fifth positive biconvex positive convex-concave lens, the second surface of the first component of the fifth lens is formed aspherical.

Positive effect: Extending the interval of changing the focal length, reducing the size and improving the 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, Ml. G 02 B 15/18, publ. 15.11.78,) containing sequentially located first stationary component consisting of one lens, a movable second a single-lens component, a movable third component, a single lens, and a stationary fourth component, a two-lens.

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), as well as a sufficiently large circle of aberration scattering from a point radiation source, 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 smoothly changing focal length (see US patent No. 6091551, M. class. G 02 B 15/14; G 02 B 13/14, publ. 18.07.2000 g ., the diagram in FIG. 6), containing the first fixed component in the form of a positive convex-concave lens, the second movable component in the form of a first negative convex-concave lens and the second negative biconcave lens, and the third mobile component in the form of a negative concave convex lens, even the fifth fixed component in the form of a positive concave-convex lens and the fifth stationary component in the form of a first positive convex-concave lens, a second negative concave-convex lens, a third positive concave-convex lens, a fourth positive convex-concave lens and a fifth plane-parallel plate.

The ratio of the maximum focal length to the minimum in this infrared lens reaches M = 4. Image quality is ensured

the ratio of the focal lengths of the components with the maximum focal length of the lens f _t : 1.00 <f ₁ / f _t , -0.40> f ₂ / f _t and 0.35 <f ₅ / f _t <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 gives a series of equations linking the optical powers of the components, analyzing which you can get the required ratio of focal lengths: f ₁ / f _t > 1, f ₂ / f _t <0, etc. In the lens construction under consideration, its length — the distance from the first lens surface to the image plane — exceeds the maximum focal length of 1.83 times, and the fifth component, consisting of five lenses, plays an important role in determining the length of the lens. The ratio of the length of this component to its focal length is 1.78. Another disadvantage of the lens is its poor aberration characteristics, and the range of focal lengths is the ratio of the maximum focal length to the minimum M = 4.

Thus, the disadvantage of the described infrared lens with a smoothly changing focal length is the small interval for changing focal lengths and large dimensions with insufficient image quality.

The problem the utility model aims to solve is to increase the interval for changing the focal length, reduce the length of the infrared lens relative to its maximum focal length, and also increase the energy concentration in a given scattering circle, which is the optimal characteristic of image quality.

This goal is achieved by the fact that in an infrared lens with a smoothly changing focal length, consisting of sequentially located stationary first component containing a positive convex-concave lens, mounted to move along the optical axis of the movable second component containing a negative convex-concave lens, and a third component made in the form of a negative concave-convex lens, stationary fourth component made in the form of a positive concave-you ukloy

lenses, and the fifth component containing the first and second positive convex-concave lenses, the second negative convex-concave, the third negative biconcave, the fourth positive biconvex, and the fifth positive convex-concave lens are additionally introduced into the first component. The second surface of the first lens of the fifth component is made aspherical. Aspherical surface is made in accordance with the equation

y ² + z ² = 188.523x-1.8124x ² + 0.1957x ³ -0.0609x ⁴ ,

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 that coincides with the optical axis of the lens.

Introduction to the first component of an additional four lenses of the described configuration allows to increase, compared with the prototype, the interval of smooth change of the focal length of the lens to 8.3 times (in prototype-4), as well as reduce the dimensions of the lens as a whole to the ratio of its length to the focal length a distance of up to 1.6 (in the prototype-1.83) while improving image quality.

The execution of the second surface of the first lens of the fifth aspherical component, as well as the selection of the equations for this aspherical surface, made it possible to perform the required correction of the lens aberrations not only over the entire image field, but also over the entire interval of smooth change in its focal length, ensuring the maximum energy concentration in the spot of the diffraction diameter to achieve high image quality.

The drawing shows an optical diagram of an infrared lens with a smoothly changing focal length from 59.124 to 500.14 mm with an arrangement of lenses for a focal length of 59.124 mm.

The lens contains sequentially located along the optical axis of the stationary first component I, consisting of a positive convex-concave lens 1, a second negative convex-concave lens 2,

the third negative biconcave lens 3, the fourth positive biconvex lens 4 and the fifth positive convex-concave lens 5, the second component II moving along the optical axis, consisting of the negative convex-concave lens 6, the third component III moving along the optical axis, consisting of the negative concave convex lens 7, the motionless fourth component IV, consisting of a positive concave-convex lens 8, and the motionless fifth component V, consisting of a first positive convex-concave lens 9 and a second position convex-concave lens 10. The second surface of the first lens 9 of the fifth component V is aspherical.

The aspherical surface of the first lens 9 of the fifth component V is made in accordance with the equation

y ² + z ² = 188.523x-1.8124x ² + 0.1957x ³ -0.0609x ⁴ ,

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 that coincides with the optical axis of the lens.

The design parameters of the inventive infrared lens with a smoothly changing focal length from 59.124 to 500.14 mm for the spectral region 3-5 μm with the location of the lenses for the focal length 59.124 mm are presented in table 1.

A lens with a smoothly changing focal length works as follows: a parallel beam of infrared rays passes through all the lenses of the lens, refracted on each surface in accordance with the radii and materials of the lenses, and focuses on the optical axis in the focal plane. The diameter of the beam is determined by the diameter of the aperture diaphragm located on the first surface of the lens 9. Inclined beams of rays also pass through all the lenses of the lens and are focused accordingly at another point in the focal plane.

Table 1 Component No. Lens number The value of the radius of the spherical surface, mm Axial thickness, mm Material I one r1 = 671.71
r2 = 1105.91 d1 = 22 Germanium d2 = 200 2 r3 = 431.93
r4 = 329.62 d3 = 10 Germanium d4 = 16 3 r5 = -615.75
r6 = 1231.81 d5 = 10 Germanium d6 = 10 four r7 = 1972.72
r8 = -486.1 d7-12 Silicon d8-5 5 r9 = 297.53
r10 = 366.87 d9 = 10 Silicon d10 = 29.2 II 6 r11 = 89.23
r12 = 76.43 d11 = 9 Germanium d12 = 259.5 III 7 r13 = -159.94
r14 = -1277.71 d13 = 5 Germanium d14 = 65.79 IV 8 r15 = 338.69
r16 = -165.04 d15 = 5 Silicon V d16 = 5 9 r17 = 87.35
r18 = 94.2615 ^*) d17 = 4 Silicon d18 = 70 10 r19 = 105.05
r20 = 286.77 d19 = 4 Silicon ^*) Aspherical surface of the form
² + z ² = 188.523x-1.8124x ² + 0.1957x ³ -0.0609x ⁴ .

Changing the focal length of the lens is done by moving components II and III along the optical axis of the lens. The values of the variable air gaps d10, d12 and d14 for the three values of the focal lengths of the lens are shown in table 2.

table 2 Focal length of the lens, mm d10 mm d12 mm d14 mm 500.14 340.09 9.3 5.1 260.08 292.0 23.33 39.16 59,124 29.2 259.5 65.79

The table shows that the ratio of the maximum value of the focal length to the minimum M = 8.3.

With the claimed design, the length of the lens is 803.49 mm and does not exceed the maximum focal length more than 1.6 times.

The energy concentration in the spot of a given diameter of 50 μm, which characterizes the image quality, is presented in table 3 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 The lens is a prototype. Focal length mm 59,124 260.08 500.14 fifty one hundred 200 Energy concentration,% 80 86 86 35 23 76

In the proposed lens with a smoothly varying focal length, the introduction into the design of the first component of an additional four lenses of the described configuration and the second surface of the first lens of the fifth aspherical component made it possible to increase the interval of change of the focal length of the lens, reduce its dimensions and improve image quality compared to the prototype.

Claims (3)

1. An infrared lens with a smoothly changing focal length, consisting of a series of stationary stationary first component containing a positive convex-concave lens, mounted to move along the optical axis of the movable second component containing a negative convex-concave lens, and a third component, made in the form negative concave-convex lens, motionless fourth component, made in the form of a positive concave-convex lens, and the fifth component, soda holding the first and second positive convex-concave lenses, characterized in that the second component is additionally introduced a second negative convex-concave, third negative biconcave, fourth positive biconvex and fifth positive convex-concave lens. 2. The infrared lens according to claim 1, characterized in that the second surface of the first lens of the fifth component is made aspherical. 3. The infrared lens according to claim 2, characterized in that the aspherical surface of the first lens of the fifth component is made in accordance with the equation y ² + z ² = 188.523x-1.8124x ² + 0.1957x ³ -0.0609x ⁴ , where y is the axis of the coordinate system lying in the plane of the meridian 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.