RU2384869C1 - Large-aperture lens - Google Patents

Abstract

FIELD: physics, optics.

SUBSTANCE: large-aperture lens can be used in night vision devices. The large-aperture lens has a positive and a negative meniscus along the beam path whose convex sides face the object side, an aperture diaphragm, a negative component made from a biconcave and a biconvex lens glued together, a biconvex lens and a positive meniscus whose concave side faces the image. The focal distance of the lens, radii of certain surfaces, thickness of the second meniscus, the Abbe number and refraction indices of the last three elements are related through expressions given in the formula of invention.

EFFECT: increased aperture ratio and viewing angle with good image quality.

1 dwg, 2 tbl

Description

The invention relates to the field of optoelectronic technology and can be used in night vision devices.

A known modified Gaussian type lens (patent DD 245059, class G02B 9/62, published in 1987) containing a positive meniscus located along the beam, a component glued from two menisci facing concavity to the diaphragm, a component glued from biconcave and a biconvex lens, a biconvex lens, and a positive meniscus with a concavity toward the image.

The lens has an aperture of 1: 1.4 and an angle of field of view of 35 °. In a similar lens according to patent RU 2315341 C1, publ. 01/20/2008, the second component is made in the form of a single negative meniscus, and the fifth component is in the form of a convex-flat lens; the lens has an aperture of 1: 1.5 and a field of view angle of 18 degrees. 20 minutes.

The closest to the proposed invention according to the optical design and the achieved result is a fast lens (DE 41 02377 A1, publ. 1991), including positive and negative menisci located along the beam, convex towards the object, aperture diaphragm and filter, positive component, glued from a biconcave and biconvex lens, a biconvex lens and a positive meniscus facing concavity to the image, the following conditions being met:

;

;

;

;

;

;

,

;

;

,

where f 'is the focal length of the lens;

r ₃ and r ₄ are the radii of the second meniscus;

r ₇ and r ₉ are the radii of the front and rear surfaces of the third (glued) component;

d ₂ is the thickness of the second meniscus;

n ₄ , n ₅ , n ₆ , n ₇ are the refractive indices of the corresponding element;

υ ₅ , υ ₆ , υ ₇ is the Abbe number of the corresponding element (three rear lenses).

However, this lens also has a relatively low aperture ratio of 1: 1.4 and a field angle of 2ω = 40 °.

The objective of the invention is to create a high-aperture lens with increased relative aperture and field of view angle with good image quality.

The technical result due to the task is achieved by the fact that in a fast lens, including positive and negative menisci located along the beam, convex towards the object, an aperture diaphragm, a component glued from a biconcave and biconvex lens. a biconvex lens and a positive meniscus facing concavity to the image when the following conditions are met:

unlike the well-known, the double-glued component is negative and the conditions are additionally introduced:

,

,

where f 'is the focal length of the lens;

r _i is the radius of the corresponding surface of the element;

d ₃ - the thickness of the second meniscus;

n _i is the refractive index of the corresponding element;

υ _i is the Abbe number of the corresponding element.

Since the optical circuits of the lens and its prototype are different, the numbering of the structural elements has slightly changed. So, d _{3 of the} lens corresponds to d _{2 of the} prototype, ar ₇ and r _{5 of the} lens corresponds to r ₉ and r _{7 of the} prototype.

Fulfillment of the indicated conditions, in particular, the fulfillment of the double-glued component with a negative and steeper radius of the rear surface when the refractive index of the front lens is exceeded by more than 0.03, makes it possible to increase the field of view angle from 40 ° to 48 ° and the relative aperture from 1: 1.4 to 1: 1.3.

The drawing shows an optical diagram of the proposed lens.

The lens consists of a successive single meniscus 1 and a single negative meniscus 2, convex to the object, an aperture diaphragm 3, a biconcave lens 4, glued with a biconvex lens 5, a biconvex single lens 6, and a single positive meniscus 7. Two-glued component overall is negative. Behind the lens, a plane-parallel plate 8 is installed, which also acts as a light filter for the spectral region of 0.55-0.95 μm.

The proposed optical circuit operates as a lens. The light flux from an object located at infinity falls into the lens, where the light filter 8 passes through the lenses 1, 2, 4, 5, 6, 7 and forms an image of the object in the plane of the best setup in which the optical radiation receiver is installed.

The design parameters of the lens are shown in table 1:

Table 1 Radius mm Thickness mm Glass mark Impression prel. n _e Coeff. Disp. υ _e Lens diameter mm r ₁ = 19.815 d ₁ = 3,5 Bf-16 1.67438 47.00 21 r ₂ = 57.02 d ₂ = 1.17 21 r ₃ = 12.531 d ₃ = 4.91 TF5 1.76171 27.32 fifteen r ₄ = 7,112 d ₄ = 8.21 10 r ₅ = -7.586 d ₅ = 0.83 TF5 1.76171 27.32 9.8 r ₆ = 25.94 d ₆ = 4.06 STK3 1,66224 57.09 12.9 r ₇ = -10.593 d ₇ = 0.1 12.9 r ₈ = 159.96 d ₈ = 4 STK3 1,66224 57.09 16,2 r ₉ = -15,417 d ₉ = 1.37 18.0 r ₁₀ = 17.947 d ₁₀ = 3,5 STK3 1,66224 57.09 20.8 r ₁₁ = 48.19 20.8

The following conditions are fulfilled in the lens:

r ₃ -r ₄ -d ₃ = 0.509, which with f '= 20.3 mm is in the range of 0.02 f' ... 0.05 f ', as claimed in the prototype;

, т.е. больше 51, как и в прототипе;

, i.e. more than 51, as in the prototype;

r ₇ : r ₅ = 10.593: 7.586 = 1.39, i.e. more than 1.3 declared in the prototype;

n ₄ -n ₅ = 1.76171-1.66224 = 0.1, i.e. more than 0.03 (the prototype 0.027);

, т.е. меньше 1,73, заявленных в прототипе.

, i.e. less than 1.73 declared in the prototype.

The lens has the following specifications:

- focal length 20.3 - relative hole 1: 1.3 - angle of view 48 ° - back section (without plate) 13.96 mm

The lens is designed to work in night devices. It gives an image of objects on the photocathode of the image intensifier tube. The lens is designed together with a protective plane-parallel plate 8 of the image intensifier tube, which also acts as a light filter in the spectral region of 0.55-0.95 μm and is located near the focal plane of the lens.

The image quality of the lens is characterized by its contrast transfer coefficients (CPC). Table 2 compares the PDA (K) of the proposed lens and prototype:

table 2 PDA Lens Prototype N = 20 lines / mm N = 50 lines / mm N = 20 lines / mm N = 50 lines / mm 1. For a point on the axis 0.816 0.628 0.835 0.451 2. For the field zone ω ₁ = 11 ° 40 ' - meridional 0.690 0.398 0.560 0.288 - sagittal 0.760 0.602 0.654 0.334 section 3. For the field zone ω ₁ = 20 ° - meridional 0.713 0.247 0.291 0.105 - sagittal 0.628 0.180 0.647 0.220 section 4. For the edge of the field ω ₁ = 24 ° - meridional 0.590 0.140 0,031 0.006 - sagittal 0.694 0.217 0.450 0.144 section

Thus, in the proposed lens, a technical result is obtained: when the relative aperture is increased 1: 1.3 and the field of view angle is increased to 48 °, a high image quality is achieved.

Claims (1)

A fast lens, including positive and negative menisci located along the beam, convex towards the object, an aperture diaphragm, a component glued from a biconcave and biconvex lens, a biconvex lens and a positive meniscus facing concavity to the image, under the conditions

characterized in that the double-glued component is negative and the conditions are additionally fulfilled

where f 'is the focal length of the lens;
r _i is the radius of the corresponding surface of the element;
d ₃ - the thickness of the second meniscus;
n _i is the refractive index of the corresponding element;
υ _i is the Abbe number of the corresponding element.