RU2746941C1 - Optical system - Google Patents

Abstract

FIELD: optical systems.

SUBSTANCE: optical system can be used in television and photographic systems, as well as in measuring devices with multi-element matrix radiation detectors. The optical system consists of the first lens group containing the first negative convex-concave, the second positive convex-concave, the third negative convex-concave lens, the second lens group containing the first negative convex-concave, the second biconvex, the third negative concave-convex and fourth negative a concave-convex lens, and a radiation receiver. The following relations are fulfilled: -6,3≤fʹ₁/fʹ≤-5,3; 0,7≤fʹ_II/fʹ≤1,3; 1,2≤d_1-2/fʹ≤1,8; 0,4≤d_6-7/fʹ≤0,6, where fʹ₁ is the focal length of the first lens of the first lens group; fʹ_II - focal length of the second lens group; d_1-2 is the distance between the first and second lenses of the first lens group, d_6-7 is the distance between the third and fourth lenses of the second lens group; fʹ - focal length of the system.

EFFECT: technical result is an increase in the relative aperture of the optical system while reducing its length, simplifying the design and high image quality within the entire field of view.

1 cl, 4 tbl, 2 dwg

Description

The invention relates to optical instrumentation and can be used to create television and photographic systems, as well as in measuring instruments with multi-element matrix radiation detectors.

Known lens (see patent for utility model RU 147364 U1, IPC ⁷ G02B 9/12, 11/12, publ. 10.11.2014) with a focal length of 50 mm, aperture ratio of 1: 2.94 and an angular field of view of 35 °. The disadvantages of this lens are the presence of two aspherical surfaces, which increase manufacturing costs, and the high distortion value at the edge of the field of view (-6%).

The closest in technical essence to the claimed system, adopted as a prototype, is a telecentric lens (see patent RU 2278403 C1, IPC ⁷ G02B 13/22, 9/64 publ. 20.06.2006). The lens consists of two lens groups containing four and seven lenses, respectively. In the first group, the first lens is made negative convex-concave, the second is biconcave, the third is biconvex, and the fourth is positive concave-convex. In the second group, the first lens is negative convex-concave, the second is biconvex, the third is negative concave-convex, the fourth is negative convex-concave, the fifth is biconvex, the sixth is negative convex-concave, the seventh is positive convex-concave. An aperture diaphragm is located in the space between the groups. The lens is designed to operate in the spectral range of the spectrum from 0.5 to 0.9 microns, has a focal length f = 40 mm, relative aperture 1: 6, angular field of view 54 °. The length from the first surface to the plane of the sensitive elements of the matrix radiation detector (MRR) is L = 201.7 mm.

The disadvantages of this lens include a low relative aperture, long length and a large number of lenses. In addition, the given values of the MTF (modulation transfer function) indicate a low quality of its image. The best MTF values are obtained for the spectral range of 0.5-0.6 μm and are 0.67 for 70 lines / mm in the center of the field of view, 0.58 in the meridional section (m) and 0.64 in the sagittal section ( s), at the edge of the field of view - 0.43 (m) and 0.56 (s).

The problem to be solved by the invention is to increase the relative aperture of the optical system while reducing its length, simplifying the design and high image quality within the entire field of view.

This goal is achieved by the fact that in the optical system, consisting of the first lens group located along the optical axis, containing the first negative convex-concave, second and third lenses, and the second lens group containing the first negative convex-concave, second biconvex, third negative concave - convex and fourth negative lenses, and a radiation receiver, in the first group the second lens is made positive convex-concave, the third one is negative convex-concave, and in the second group the fourth lens is made concave-convex, while the following relations are fulfilled:

-6.3≤f ' ₁ / f'≤ -5.3;

0.7 f ' _II / f'1.3;

1.2 d _1-2 / f '1.8;

0.4≤d _6-7 / f'≤0.6,

where f ' ₁ is the focal length of the first lens of the first lens group; f ' _II - focal length of the second lens group; d _1-2 is the distance between the first and second lenses of the first lens group, d _6-7 is the distance between the third and fourth lenses of the second lens group; f 'is the focal length of the system.

Figure 1 shows a diagram of an optical system.

Figure 2a presents plots of the MTF of the system, where the maximum value of the spatial frequency (117 lines / mm) is determined for the pixel size of the radiation receiver (4.25 μm).

Figure 26 is a graph of the distortion of the optical system.

The optical system consists of the first lens group I located along the optical axis, containing the first negative 1, the second positive 2 and the third negative 3 convex-concave lenses, and the second lens group II, containing the first negative convex-concave 4, the second biconvex 5, the third negative the concave-convex 6 and the fourth negative concave-convex lens 7, and the radiation receiver 8. The system satisfies the following ratios: -6.3 f ' ₁ / f' 5 -5.3; 0.7 f ' _II / f'1.3; 1.2 d _1-2 / f '1.8; 0.4≤d _6-7 / f'≤0.6, where f ' ₁ is the focal length of the first lens 1 of the first lens group I; f ' _{II is the} focal length of the second lens group II; d _1-2 is the distance between the first 1 and the second 2 lenses of the first lens group I, d _6-7 is the distance between the third 6 and the fourth 7 lenses of the second lens group II; f 'is the focal length of the system. The first surface of the first lens 5 of the second group II is the aperture diaphragm of the system.

Table 1 shows the design parameters of an example of the implementation of the optical system.

Table 2 shows the ratios performed in the claimed system, where f ' ₁ is the focal length of the first lens 1 of the first lens group I; f ' _II - focal length of the second lens group II; d _1-2 is the distance between the first 1 and the second 2 lenses of the first lens group I, d _6-7 is the distance between the third 6 and the fourth 7 lenses of the second lens group II; f 'is the focal length of the system.

Table 3 lists the technical characteristics of the optical system.

Table 4 shows the MTF values of the system for 70 lines / mm in the entire spectral range for the center, middle and edge of the field of view.

As follows from table 3, the relative aperture of the claimed system is increased by 1.5 times compared to the prototype, while the length has decreased by 1.9 times. In contrast to the prototype, the claimed system contains seven optical elements, and in the first lens group there was one less lens, and in the second - by three.

An increase in the relative aperture, a decrease in the length and number of elements while ensuring high image quality is achieved by choosing the focal lengths of the lenses and lens groups, their relative position when performing the ratios given in Table 2, and the appropriate choice of materials.

From the MTF plots shown in figure 2 (a), it follows that the optical system has high image quality in a wide spectral range within the entire field of view. As can be seen from table 4, the values of the MPF for 70 lines / mm in the inventive system significantly exceed those of the prototype. From the graph shown in figure 2 (b), it follows that the system has a well-corrected distortion within the entire field of view, which makes it possible to use it in measuring instruments.

The optical system works as follows: the radiation flux passes through the lenses 1-7 of the system, is refracted on each surface in accordance with the radii of curvature and lens materials and is focused in the plane of the sensitive elements of the radiation receiver 8. The radiation beam diameter is determined by the diameter of the aperture diaphragm coinciding with the first surface of the first lenses 5 of the second group II.

Thus, the implementation of the optical system in accordance with the proposed technical solution provides an increase in the relative aperture while reducing the length, simplifying the design and high image quality within the entire field of view.

Claims (6)

An optical system consisting of a first lens group located along the optical axis, containing the first negative convex-concave, second and third lenses, and a second lens group containing the first negative convex-concave, second biconvex, third negative concave-convex and fourth negative lenses, and a radiation receiver, characterized in that in the first group the second lens is made positive convex-concave, the third one is negative convex-concave, and in the second group the fourth lens is made concave-convex, while the following relations are fulfilled: -6.3≤f ' ₁ / f'≤ -5.3; 0.7 f ' _II / f'1.3; 1.2 d _1-2 / f '1.8; 0.4≤ d _6-7 / f'≤0.6; where f ' ₁ is the focal length of the first lens of the first lens group; f ' _II - focal length of the second lens group; d _1-2 is the distance between the first and second lenses of the first lens group, d _6-7 is the distance between the third and fourth lenses of the second lens group; f 'is the focal length of the system.

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