RU2560748C1 - Large aperture optical system - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: device comprises positive and negative meniscus lenses arranged along the beam and with their convexity facing the subject, aperture diaphragm, negative component glued of biconcave lens and biconvex lens, biconvex lens and positive meniscus lens with its concavity facing the image. Negative meniscus lens satisfies the following terms: 2.5 mm≤r₄(r₃-d₃)/[n₂r₄-(n₂-1)(r₃-d₃)]≤2.7 mm; 1.723≤n₂≤1.734; 27.9≤υ₂≤29.3, where r₃ and r₄ are negative meniscus lens radii; d₃ is negative meniscus lens depth; n₂ is negative meniscus refractive exponent; υ₂ is negative meniscus lens Abbey number.

EFFECT: improved manufacturability, high image quality.

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Description

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

A known lens of the modified Gaussian type (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 a small field of view angle of 35 °. In a similar lens according to patent RU 2315341 C1, publ. 01/20/2008, the lens contains five components, the first of which (along the beam) is a single positive meniscus convex to the object, the second component is a single negative meniscus convex to the object, and the third component is a double-glued meniscus facing an external convex surface to the image, consisting of negative and positive lenses, the fourth and fifth components are single positive lenses; the lens has a focal length of 24.95 mm, aperture ratio of 1: 1.5 and a field of view angle of 18 degrees. 20 minutes. The distance Δ ₂ between the autocollimation points in the second component, determined by the formula connecting the radii r ₃ and r _{4 of the} lens and the refractive index of its material n ₂ (Elnikov N.T., Ditev A.F., Yurusov I.K., Assembly and adjustment of optical-mechanical devices. M.: Mechanical Engineering, 1974, S. 114-115), equal to:

Δ ₂ = r ₄ (r ₃ -d ₃ ) / [n ₂ r ₄ - (n ₂ -1) (r ₃ -d ₃ )] = 6.85 mm.

As you can see, the distance between the autocollimation points of the second component is quite large, however, this lens has a small angle of view and a relative aperture, which does not allow us to solve the problem.

The closest in design to the proposed is a fast lens according to patent RU 2384869 C1, publ. 03/20/2010, consisting of a single positive meniscus and a single negative meniscus sequentially located along the beam, convex to the object, an aperture diaphragm, a biconcave lens glued to a biconvex lens, a biconvex single lens, and a single positive meniscus. A plane-parallel plate is installed behind the lens, which also acts as a light filter for the spectral region 0.55-0.95 μm. The lens has high image quality and the following technical specifications:

focal length of the lens f ′ = 20.3 mm;

posterior focal segment (without plate) S ′ _{F ′} = 13.96 mm;

relative aperture - 1: 1.3;

the angular field in the space of objects is 48 °.

In the lens, the distance between the autocollimation points of the negative (second along the ray) meniscus is Δ ₂ = r ₄ (r ₃ -d ₃ ) / [n ₂ r ₄ - (n ₂ -1) (r ₃ -d ₃ )] = 0 , 95 mm, which characterizes the low manufacturability of manufacturing the specified meniscus, and also reduces the accuracy of assembly and control of the lens as a whole.

The technical result of the invention is to increase the manufacturability of the manufacture of the lens while maintaining the technical characteristics, quality of the image.

The technical result 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 turned by concavity towards unlike the known, the negative second meniscus is made with the conditions:

2.5 mm≤r ₄ (r ₃ -d ₃ ) / [n ₂ r ₄ - (n ₂ -1) (r ₃ -d ₃ )] ≤2.7 mm;

1.723≤n ₂ ≤1.734;

27.9≤υ ₂ ≤29.3,

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

d ₃ - the thickness of the second meniscus;

n ₂ is the refractive index of the second meniscus along the ray;

υ ₂ is the Abbe number of the second meniscus along the ray.

Fulfillment of these conditions, in particular, the fulfillment of a negative meniscus with a steeper radius of the rear surface with a simultaneous decrease in thickness d ₃ and provided that the refractive index of the second meniscus is in the range from 1.723 to 1.734 and the Abbe number is in the range from 27.9 to 29 3, allows to increase the distance between the autocollimator points from the first and second surfaces of a negative meniscus (2,5 mm≤Δ ≤2,7 ₂ mm), which in turn increases the manufacturability of the optical components and the lens as a whole maintained at NII performance characteristics of the prototype.

The drawing shows an optical diagram of the proposed lens.

The lens consists of a successive single meniscus 1, 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 there is a plane-parallel plate 8, which also acts as a light filter for the spectral region of 0.55-0.95 microns. 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 for two versions are given in tables 1 and 2.

The stated limits of the values of the refractive index and the dispersion coefficient of the negative meniscus are fulfilled in the lens, and when substituting the values of r ₃ , r ₄ , n ₂ in the algebraic formula, the distance between the autocollimation points Δ ₂ will be in the range from 2.5 to 2.7 mm.

The lens has the following specifications (for two versions):

focal length of the lens f = 20.4 mm;

posterior focal segment (without plate) S ′ _{F ′} = 13.6 mm;

relative aperture - 1: 1.3;

the angular field in the space of objects is 48 °.

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 3 compares the PDA of the proposed lens and prototype options.

Thus, in the proposed lens variants, a technical result is obtained in comparison with the closest analogue: with a high relative aperture of 1: 1.3 and a field of view angle increased to 48 °, an increase in the distance between the autocollimation points from the first and second surfaces of the second (along beam) component (2.5 mm≤Δ ₂ ≤2.7 mm), which, in turn, increases the manufacturability of the manufacture of optical parts and the lens while maintaining high (at the prototype level) values of the CCP.

Claims (1)

A fast lens, including positive and negative menisci, convex towards the subject, an aperture diaphragm, a component glued from a biconcave and biconvex lens, a biconvex lens and a positive meniscus, facing concavity to the image, characterized in that the negative meniscus is made with the following conditions:
2.5 mm≤r ₄ (r ₃ -d ₃ ) / [n ₂ r ₄ - (n ₂ -1) (r ₃ -d ₃ )] ≤2.7 mm;
1.723≤n ₂ ≤1.734;
27.9≤υ ₂ ≤29.3,
where r ₃ and r ₄ are the radii of the negative meniscus;
d ₃ - the thickness of the negative meniscus;
n ₂ is the refractive index of the negative meniscus;
υ ₂ is the Abbe number of the negative meniscus.