RU2174695C1 - High-speed lens for near-infrared region of spectrum - Google Patents

Abstract

FIELD: optics. SUBSTANCE: high-speed lens for near-infrared region of spectrum include two components, first component being made of biconvex lens and negative meniscus facing object with concavity and second component being biconvex lens. Proposed lens is characterized by following relations: -1,3f′<r₃<-1,0f′, 0,55f′<r₅<0,67f′,

where f′ is focal distance of entire lens;

is focal distance of lens of second component; r₃ is first curvature radius of second lens of first component; r₅ is first curvature radius of lens of second component. Invention provides for design of high-speed lens with angular field in space of objects over 13 degrees, with length of optical system less than 1,6f′ and rear focal length

Description

 The present invention relates to optical instrumentation, and in particular to special lenses of telescopic systems for observing optical devices for infrared rays, and can be used in night vision devices.

 Known designs for fast lenses, described, for example, in Japanese Patent Laid-Open N 60-64318 (A), cl. G 02 B 9/16, publ. 04/12/85, and N 52-71253 (A), class. 104A412, publ. 06/14/77

The closest analogue to the claimed technical solution is the lens described in the accepted application of Japan N 60-49288 (B2), cl. G 02 B 13/00, publ. 11.11.85 g. It contains the following sequentially arranged components:
- the first component is a biconvex lens and a negative meniscus facing concavity to the object,
- the second component is the positive meniscus, convex to the subject. The following relationships hold:
-1.65 f <r ₃ <-1.0 f,
0.42 f <r ₅ <0.56 f,
f ₃ <0.8 f,
where f is the focal length of the lens,
f ₃ - the focal length of the lens of the second component,
r ₃ is the first radius of curvature of the second lens of the first component,
r ₅ is the first radius of curvature of the lens of the second component.

This lens has a small angular field in the space of objects 2 σ = 2 ^o 4 'and a large optical system length of 1.9 f.

The objective of the invention is to create a high-aperture lens with an angular field in the space of objects greater than 13 ^o , the length of the optical system is less than 1.6 f 'and the rear focal length S' _F > 0.4 f 'with good image quality along the field.

The technical result due to this problem is achieved by the fact that in a fast lens for the near infrared region of the spectrum containing two components, the first of which consists of a biconvex lens and a negative meniscus facing concavity to the object, the second is a positive lens, in contrast to the known , in the second component, the positive lens is made in the form of a biconvex, with the following relationships:
-1.3 f '<r ₃ <-1.0 f',
0.55 f '<r ₅ <0.67 f',
0.8 f '<f' ₃ <1.1 f ',
where f 'is the focal length of the entire lens,
f ' ₃ is the focal length of the lens of the second component,
r ₃ is the first radius of curvature of the second lens of the first component,
r ₅ is the first radius of curvature of the lens of the second component.

 In FIG. 1 is an optical diagram of a lens; FIG. 2 and 3 are graphs of lens aberrations.

The lens (Fig. 1) contains two components sequentially located along the beam, the first of which consists of a biconvex lens 1 and a negative meniscus 2, facing concavity to the subject. The second component is a biconvex lens 3. The following relationships occur in the lens:
-1.3 f '<r ₃ <-1.0 f',
0.55 f '<r ₅ <0.67 f',
0.8 f '<f' ₃ <1.1 f ',
where f 'is the focal length of the entire lens,
f ' ₃ is the focal length of the lens of the second component,
r ₃ is the first radius of curvature of the second lens of the first component,
r ₅ is the first radius of curvature of the lens of the second component.

 The aperture diaphragm is located behind the lens 2.

 The lens works as follows. A parallel light flux from an object located at infinity enters the lens, where it passes sequentially through lenses 1, 2 and 3 and forms an image of the object in the plane of the best lens mount in which the optical image receiver (not shown) is installed.

As a specific example of implementation of the invention, a lens with the following structural data is calculated:
The focal length of the lens - f '= 50 mm
The focal length of the first lens is f ' ₁ = 57.68 mm
The focal length of the second lens is f ' ₂ = -117.34 mm
The focal length of the third lens is f ' ₃ = 48.21 mm
Rear focal length - S '_F' = 22.24 mm
The distance from the last surface of the lens to the plane of the best installation - S ' _mouth = 22.21 mm
The results are presented in the table.

The following ratios are observed in the lens:
-1.3 f '= -65 mm <r ₃ = -58.34 mm <-1.0 f' = -50 mm
0.55 f '= 27.5 mm <r ₅ = 31.77 mm <0.67 f' = 33.5 mm
0.8 f '= 40 mm <f' ₃ = 48.21 mm <1.1 f '= 55 mm
The calculated lens has the following characteristics:
relative aperture = 1: 1.6,
angular field in the space of objects 2 σ = 13 ^o 12 ',
spectral range (0.78 ... 0.68 ... 0.9) μm,
the length of the optical system L = Σd + S _{F ′} , = 57.2 + 22.24 = 79.44 = 1.59f ',
where Σd is the sum of the thicknesses and air gaps in the lens,
S '_F' - the back section,
longitudinal spherical aberration in the area of (-0.003) mm,
image meridional curvature along the field (-0.191) mm,
sagittal image curvature along the field (-0.146) mm.

 The aperture diaphragm is located behind the lens 2 at a distance of 11 mm from it, the diameter of the aperture diaphragm is 24.5 mm.

Thus, as a result of the proposed solution, a technical result is obtained in comparison with the closest analogue: the angular field in the space of objects is 2 σ = 13 ^o 12 ', the length of the optical system is reduced to 1.59 f' instead of 1.92 f ', the rear focal the segment is increased to 0.44 f 'with a high relative aperture of the lens 1: 1.6 and good image quality in the field:
longitudinal spherical aberration in the area of (-0.003) mm,
image meridional curvature (-0.19) mm,
sagittal image curvature (-0.15) mm.

Claims (1)

A high-speed lens for the near infrared region of the spectrum containing two components, the first of which consists of a biconvex lens and a negative meniscus facing concavity to the object, the second is a positive lens, characterized in that in the second component the positive lens is made in the form of a biconvex, The following relationships hold:
-1.3 f '<r ₃ <-1.0 f',
0.55 f '<r ₅ <0.67 f',
0.8 f '<f' ₃ <1.1 f ',
where f 'is the focal length of the entire lens;
f ' ₃ is the focal length of the lens of the second component;
r ₃ is the first radius of curvature of the second lens of the first component;
r ₅ is the first radius of curvature of the lens of the second component.

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