RU104331U1 - INFRARED LENS WITH FULLY VARIABLE FOCUS DISTANCE - Google Patents

Abstract

 Infrared lens with a smoothly varying focal length, containing successively arranged stationary first component in the form of a positive convex-concave lens, a movable second component consisting of a first negative convex-concave lens and a second negative lens, a movable third component and a stationary last component containing the first positive a convex-concave lens and a second lens, characterized in that in the second component the second lens is biconcave, the third component is n a positive biconvex lens, the last component of the second negative lens is formed concavo-convex, wherein the focal length f1 of the first component is selected according to the maximum focal distance of the infrared lens as follows: f1 = (from 0.545 to 0.8) ft,! where f1 is the focal length of the first component; ! ft is the maximum focal length of the lens.

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 US patent No. 6091551, M. CL G02B 15/14; G02B 13/14, publ. July 18, 2000, the circuit in Fig.6), containing a fixed component in series I with a focal length f ₁ consisting of a positive convex-concave lens, a movable component II with a focal length f ₂ , consisting of a first negative convex-concave lens and a second negative biconcave lens, a movable component III with a focal length f ₃ , consisting of a negative concave convex lens further fixed components IV with a focal length f ₄ , consisting of a positive concave-convex lens, and the last component V with focal length f ₅ , consisting of a first positive convex-concave lens, a second negative concave-convex lens, and a third positive concave-convex lenses and the fourth positive convex-concave lens.

The focal length of the lens varies from 50 mm to 200 mm. The ratio of the maximum focal length to the minimum in this infrared lens reaches m = 4. Image quality is ensured by the specified limits of the ratio of the focal lengths of the components with the maximum focal length of the lens f _t , in particular, f ₁ > f _t . In the lens construction under consideration, its length — the distance from the first surface of the lens to the image plane — exceeds the maximum focal length by 1.83 times.

The disadvantage of this infrared lens is the large size and number of components.

These shortcomings were partially eliminated in the infrared lens closest in technical essence with a smoothly changing focal length (see RF patent No. 2321873, M. cl. G02B 15/16, G02B 13/14, publ. 10.04.2008 Bull. No. 10), comprising a successively arranged stationary first component in the form of a positive convex-concave lens, a movable second component consisting of a first negative convex-concave lens and a second negative lens made of a convex-concave lens, a movable third component in the form of a concave-convex lens, motionless th fourth component in the form of concavo-convex lenses and the last component, consisting of two convex-concave lenses. The focal length of the first component is selected from the relation f ₁ = (from 0.804 to 0.948) f _t . The ratio of the distance from the first surface of the lens to the image plane to the maximum focal length is 1.35.

The disadvantage of this infrared lens with a smoothly changing focal length is the significant size and a large number of components.

The problem the utility model is aimed at reducing the length of the infrared lens relative to its maximum focal length and reducing the number of components while maintaining a fairly high image quality.

This goal is achieved by the fact that in an infrared lens with a smoothly changing focal length, containing successively arranged stationary first component in the form of a positive convex-concave lens, a movable second component consisting of a first negative convex-concave lens and a second negative lens, a movable third component and fixed last component containing the first positive convex-concave lens and the second lens, in the second component the second lens is biconcave, the third Symbol Item configured as a biconvex positive lens, and the last component of the second negative lens is formed concavo-convex, wherein the focal length f ₁ of the first component is selected according to the maximum focal length as follows:

f ₁ = (from 0.545 to 0.8) f _t ,

where f ₁ is the focal length of the first component;

f _t is the maximum focal length of the lens.

The choice of the focal length of the first component is smaller than recommended in known IR lenses with a smoothly varying focal length, and a change in the design of the last fixed component allowed us to reduce the number of components in the lens (in the prototype 5 components, in the inventive lens - 4) and its dimensions (length ratio of the inventive lens to the maximum focal length is 0.98 in contrast to 1.35 in the prototype).

The implementation of the second lens of the second component in the form of a negative biconcave lens, and the third component in the form of a positive biconvex lens made it possible to provide the necessary correction of lens aberrations to achieve the desired image quality.

The drawing shows an optical diagram of an infrared lens with a smoothly changing focal length from 50 mm to 200 mm with an arrangement of components corresponding to a maximum focal length of 200 mm.

The lens contains a stationary first component I in the form of a positive convex-concave lens 1, a movable second component II, consisting of a first negative convex-concave lens 2 and a second negative biconcave lens 3, a movable third component III in the form of a positive biconvex lens, sequentially arranged along the optical axis 4, and a fixed component IV, consisting of a first positive convex-concave lens 5 and a second negative concave-convex lens 6. The first surface of the second lens 3 of the second component This II is made aspherical.

The aspherical surface of the second lens 3 of the second component II is made in accordance with the equation:

y ² + z ² = -384.5815x + 27.9033x 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.

The focal length of the first component f ₁ = 109.15 mm, its ratio to the maximum focal length of the lens f _t = 200 mm, is 0.545.

The design parameters of the inventive infrared lens with a smoothly changing focal length from 50 to 200 mm for the spectral region of 8.0-12.0 μm with the location of the lenses for the focal length of 200 mm 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 = 111.69 d1 = 8 Germanium r2 = 160.32 d2 = 68.1 II 2 r3 = 174.58 d3 = 3 Znse r4 = 106.41 d4 = 8 3 r5 = -192.2907 ^*) d5 = 3 Germanium r6 = 98.17 d6 = 15.7 III four r7 = 377.6 d7 = 3 Germanium r8 = -325.1 d8 = 28.7 IV 5 r9 = 170.22 d9 = 3 Germanium r10 = 1527.6 d10 = 7 6 r11 = -20.32 d11 = 3 Germanium r12 = -22.59 ^*) Aspherical surface of the form: y ² + z ² = -384.5815x + 27.9033x ² .

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 beam diameter is determined by the diameter of the aperture diaphragm located on the first surface of the lens 5. Inclined beams of rays also pass through all the lenses of the lens and are focused respectively at another point in the focal plane. Changing the focal length of the lens is done by moving components II and III along the optical axis of the lens. Components II and III are each moved according to their own law. The values of the variable air gaps d2, d6 and d8 for the three values of the focal lengths of the lens are shown in table 2.

table 2 The focal length of the lens, mm d2 mm d6 mm d8 mm 200 68.1 15.7 28.7 one hundred 56.8 50.3 5,4 fifty 50.8 54.3 7.4

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

With the claimed design, the length of the lens is 196.5 mm and does not exceed the maximum focal length more than 0.98 times.

The calculated values of the energy concentration in the spot of a given diameter of 50 μm, characterizing the image quality, are presented in table 3 for three values of the focal lengths of the inventive lens and the lens taken as a prototype.

Table 3 Parameter The inventive lens Prototype lens Focal length mm fifty one hundred 200 fifty one hundred 200 Energy concentration,% 80 82 81 74 81 83

Thus, the implementation of the infrared lens with a smoothly changing focal length in accordance with the formula of the claimed materials allows to reduce the length of the infrared lens relative to its maximum focal length while maintaining a fairly high image quality.

Claims (1)

Infrared lens with a smoothly varying focal length, containing successively arranged stationary first component in the form of a positive convex-concave lens, a movable second component consisting of a first negative convex-concave lens and a second negative lens, a movable third component and a stationary last component containing the first positive a convex-concave lens and a second lens, characterized in that in the second component the second lens is biconcave, the third component is n a positive biconvex lens, the last component of the second negative lens is formed concavo-convex, wherein the focal length f ₁ of the first component is selected according to the maximum focal distance of the infrared lens as follows: f ₁ = (from 0.545 to 0.8) f _t , where f ₁ is the focal length of the first component; f _t is the maximum focal length of the lens.