RU60740U1 - 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.

Goal: Reduce the length of the infrared lens while increasing the focal length.

The essence of the utility model: In an infrared lens with a continuously varying focal length, containing 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, a movable third component, motionless fourth and the fifth component, in the second component the second negative lens is convex-concave, while the focal lengths f ₁ and f ₅ , respectively, of the first and fifth components, are selected depending on the maximum focal length of the infrared lens as follows:

f ₁ = (from 0.804 to 0.948) f _t

f ₅ = (from 0.342 to 0.346) f _t ,

where f ₁ and f ₅ are the focal lengths of the first and fifth components, respectively;

f _t is the maximum focal length of the lens.

Positive effect: Increasing the magnification of the change in focal length and reducing the size.

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, Mcl G 02 B 15/14; G 02 B 13/14, publ. 18.07.2000, the circuit in Fig.6), containing sequentially located fixed component I with focal length f ₁ , consisting of a positive convex-concave lens, movable component II with focal length f ₂ , consisting of a first negative convex-concave lens and a second negative biconcave lens, movable component III with focal length f3, further fixed components IV with focal length is 14 and the V component with focal length f ₅ .

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 and the maximum focal length of the lens f ₁ : 1.00 <f ₁ / f _t , -0.40> f ₂ / f _t and 0.35 <f ₅ / f _t <0.7. 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 small magnification of the focal length and large dimensions.

These shortcomings were partially eliminated in the infrared lens closest in technical essence to a smoothly changing focal length (see RF patent for utility model No. 52490, M. class G 02 B 13/14, G 02 B 15/14, publ. 27.03. 2006 Bull. No. 9), containing 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 biconcave lens, a movable third component, fixed

the fourth and fifth components, while the focal lengths f ₁ and f ₅ , respectively, of the first and fifth components, are selected depending on the maximum focal length f _{t of the} infrared lens in the following limits: f ₁ = (from 1.22 to 1.24) f _t , f ₅ = (from 0.41 to 0.42) f _t .

The focal length of the lens varies from 60 mm to 300 mm. The multiplicity of changes in the focal length - the ratio of the maximum focal length to the minimum in this infrared lens reaches M = 5. The ratio of the distance from the first surface of the lens to the image plane to the maximum focal length is 1.48.

The disadvantage of the described infrared lens with a smoothly changing focal length is the large dimensions with insufficient focal length variation.

The problem to which the utility model is directed is to reduce the length of the infrared lens relative to its maximum focal length while increasing the magnification of the change in focal length.

This goal is achieved by the fact that in an infrared lens with a continuously 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, motionless fourth and fifth components, in the second component the second lens is convex-concave, while the focal lengths f ₁ and f ₅ , respectively, of the first and fifth components are selected depending on the maximum focal length of the infrared lens as follows:

f ₁ = (from 0.804 to 0.948) f _t

f ₅ = (from 0.342 to 0.346) f _t ,

where f ₁ and f ₅ are the focal lengths of the first and fifth components, respectively;

f _t is the maximum focal length of the lens.

The choice of the focal lengths of the first and fifth components smaller than recommended in the known IR lenses with a smoothly changing focal length, allowed to reduce the size of the lens (the ratio of its length to the maximum focal length is 1.35 in contrast to 1.48 in the prototype) and increase the magnification changing the focal length of the lens to 5.86 (in prototype 5).

The implementation of the second negative lens of the second component in the form of a convex-concave 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 61.4 mm to 360 mm with an arrangement of components corresponding to a maximum focal length of 360 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 convex-concave lens 3, and a movable third component III in the form of a negative concave-convex lens 4, the stationary component IV in the form of a positive concave-convex lens 5 and the stationary component V, consisting of the first positive convex-concave lens 6 and the second positive uklo-concave lens 7. The second surface of the first lens 6 of the fifth component of V is formed aspherical.

The aspherical surface of the first lens 6 of the fifth component V is made in accordance with the equation

² + z ² = 730.332x-3.57413x ² -0.06271x ³ + 0.01527x 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 focal length of the first component f ₁ = 341.2 8 mm, its ratio to the maximum focal length of the lens f _t = 360 mm, is 0.948. The focal length of the fifth component is f ₅ = 123.169 mm, its ratio to the maximum focal length of the lens is 0.342.

The design parameters of the inventive infrared lens with a smoothly changing focal length from 61.4 to 360 mm for the spectral region of 8.0-12.0 μm with the location of the lenses for the focal length of 360 mm are presented in table 1.

Table 1 Component
No. Lens
No. The value of the radius of the spherical surface, mm Axial thickness, MM Material I one r1 = 386.54 d1 = 16 Germanium r2 = 601.37 d2 = 194.5 II 2 r3 = 325.86 d3 = 6 P04 r4 = 243.17 d4 = 12 3 r5 = 268.48 d5 = 6 Germanium r6 = 212.22 d6 = 19 III four r7 = -273.05 d7 = 6 Germanium r8 = -19547.0 d8 = 5.73 IV 5 r9 = -449.95 d9 = 6 Germanium r10 = -271.68 d10 = 6.6 V 6 r11 = 247.95 d11 = 6 Germanium r12 = 365.166 ^*) d12 = 119.7 7 r13 = 161.98 d13 = 6 Germanium r14 = 278.5

^*) Aspherical surface of the form

² + z ² = 730.332x-3.57413x ² -0.06271x ³ + 0.01527x ⁴ .

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 6. Inclined beams of rays also pass through all the lenses of the lens and are focused accordingly 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 360 194.5 19 5.73 180 152.45 14.68 52.1 61,4 6.45 132 80.78

The table shows that the ratio of the maximum value of the focal length to the minimum M = 5.86.

With the claimed design, the lens length is 488.53 mm and does not exceed the maximum focal length more than 1.35 times.

Calculations of the energy concentration in a spot of a given diameter of 50 μm (from 78% for a small focal length to 83% for a large focal length) showed that the image quality characteristics of the inventive lens are not inferior to the same characteristics of the prototype.

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 and increase the interval for changing the focal length while maintaining high image quality.

Claims (1)

An infrared 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 consisting of a first negative convex-concave lens and a second negative lens, a movable third component, motionless fourth and fifth components, characterized in that the second component of the second lens is formed convex-concave, while the focal lengths f ₁ and f _5, respectively, the first and fifth components vybi ayutsya depending on the maximum focal length of the infrared lens as follows: f ₁ = (from 0.804 to 0.948) f _t , f ₅ = (from 0.342 to 0.346) f _t , where f ₁ and f ₅ are the focal lengths of the first and fifth components, respectively; f _t is the maximum focal length of the lens.