RU2752813C1 - Apochromatic objective for wide spectrum area - Google Patents

Abstract

FIELD: optics.SUBSTANCE: objective can be used in telescopic systems, including astronomical telescopes for visual observation. An apochromatic objective includes two optically coupled components. The first component is a biconvex lens made of grade Y glass and the second is a double-lens positive meniscus made of grade Z glass, containing a biconcave lens made of grade X glass, the air gap between the components is d1and the air gap between the lenses of the second component is d2. Refraction indices and Abbe numbers of the glasses X, Y and Z comply with the following conditions: 1.7≤nX≤1.8 and 34≤νX≤36; 1.6≤nY≤1.7 and 51≤νY≤54, 1.6≤nZ≤1.7 and 30≤νZ≤33, and the air gaps comply with the conditions d1≤0.0018f, d2≤d1, wherein nXis the refraction index of the grade X glass; nYis the refractive index of the grade Y glass; nZis the refractive index of the grade Z glass; νXis the Abbe number of the grade X glass; νYis the Abbe number of the grade Y glass; νZis the Abbe number of the grade Y glass; f is the focal length of the objective.EFFECT: provided is simple and compact design with an extended operating spectral range (400 to 900 nm) and improved chromatic aberration correction.1 cl, 3 dwg, 1 tbl

Description

The invention relates to the field of optical instrumentation and can be used as an objective for telescopic systems for various purposes, including in astronomical telescopes for visual observation.

Known thin superapochromat of three lenses [1], consisting of two positive and one negative lenses. One positive lens and one negative lens are bonded, and the second positive lens is separated from the bonding by an air gap.

The disadvantages of this lens are the presence of gluing, low (1:15) relative aperture, significant overall length of the device, high residual chromatism of the position outside the limits of the F-C spectral region.

Known three-lens two-component Kohler apochromatic objective (Kohler) [2]. The lens consists of two components, separated by an air gap. The first component consists of one positive lens, and the second consists of a positive and negative lens glued together. The first positive lens along the path of the rays has a refractive index for the d line greater than 1.6 and the Abbe number greater than 55, and the lenses of the second component have an Abbe number less than 35, the difference in relative partial dispersions greater than 1.61 and the difference in refractive indices less than 0.05. In this case, the difference between the refractive indices of the lenses of the second component and the lens of the first component must be greater than 0.1.

The disadvantages of this lens are the presence of gluing, which limits the diameters of the lenses to be glued, stringent requirements for the optical constants of glasses, which limits the designer in choosing glasses, and a narrow working spectral range.

The closest technical solution adopted for the prototype is a two-component apochromatic lens [3], which includes two optically coupled components separated by an air gap d ₁ . The first component contains one positive lens made of Y grade glass, the second - a biconcave lens made of X grade glass and a positive meniscus made of Y grade glass, separated by an air gap d ₂ . Refractive indices and Abbe numbers of glasses X and Y satisfy the following conditions: 1.6 n _X 1.8 and 49 ν _X 55; 1.5 n _Y 1.7 and 51 ν _Y 66, d ₁ 0.005f, d ₂ d ₁ , where n _X is the refractive index of grade X glass; n _Y is the refractive index of Y-grade glass; ν _X is the Abbe number of grade X glass; ν _Y is the Abbe number of Y glass; f is the focal length of the lens.

The disadvantage of this objective is the limited working spectral range (0.434 ÷ 0.700 μm).

The technical solution is aimed at creating an apochromatic objective of a simple and compact design with an extended working spectral range (400-900 nm) and improved correction of chromatic aberrations.

The technical result is achieved in that an apochromatic lens is proposed, including two optically coupled components - the first component is single-lens, the second is two-lens, with an air gap between the components d ₁ and an air gap between the lenses of the second component d ₂ , characterized in that the biconvex lens of the first component and the positive meniscus of the second component is made of different brands of glasses Y and Z, respectively, and the refractive indices and Abbe numbers of glasses X, Y and Z satisfy the following conditions: 1.7 n _X 1.8 and 34 ν _X 36; 1.6≤ n _Y ≤1.7 and 51≤ ν _Y ≤54, 1.6≤ n _Z ≤1.7 and 30≤ ν _Z ≤33, and the air gaps satisfy the conditions

d ₁ ≤ 0.0018f, d ₂ ≤ d ₁

where

n _X is the refractive index of glass grade X;

n _Y is the refractive index of Y-grade glass;

n _Z - refractive index of glass grade Z;

ν _X is the Abbe number of grade X glass;

ν _Y is the Abbe number of Y glass;

ν _Z is the Abbe number of Y-grade glass;

f is the focal length of the lens.

The apochromat lens shown in FIG. 1 consists of two components: the first component contains a biconvex lens 1 made of Y grade glass, the second — a biconcave lens 2 made of X grade glass and a positive meniscus 4 made of Z grade glass.The first component is separated from the second by an air gap d ₁ , and the lenses of the second component are separated by an air gap d ₂ .

The air gap d ₁ is used to correct spherical aberration, and the gap d ₂ is used to correct spherochromatic aberration.

All optical surfaces are spherical.

The operation of the lens shown in FIG. 1 is carried out as follows: a parallel beam of rays from a distant object passes through the entrance pupil of the objective, which coincides with the first surface, and, having refracted successively through the surfaces of three lenses, builds an image of this object in the focal plane F '.

Below is an example of a specific implementation of the proposed lens. The following lens is calculated as an example:

focal length F '- 1021 mm;

back section - 973.14 mm;

relative aperture - 1:10;

working spectral range of the objective - 400 ÷ 900 nm;

angular field in the space of objects - +/- 0.25 °.

The design parameters of the calculated objective are given in Table 1. Lines "1", "2", "3" indicate the radii of curvature, thickness, refractive indices and Abbe numbers for three lenses. Line “d ₁ ” indicates the air gap between the components, and line “d ₂ ” indicates the air gap between lenses 2 and 3.

The high quality of the image created by the proposed apochromatic objective is confirmed by the graphic materials shown in Fig. 2 and FIG. 3.

FIG. 2. shows a graph of longitudinal chromatic aberration for the spectral range of 400-900 nm. The abscissa is the longitudinal chromatic aberration in microns, the ordinate is the wavelength in nanometers. The S-shaped character of the longitudinal chromatic aberration curve is clearly visible, which indicates that in the proposed lens in the specified spectral range, three wavelengths are brought together in one focus, and thus a high degree of correction of the longitudinal chromatic aberration is achieved, the value of which in this example is 153. 5 microns.

FIG. 3 shows a graph of the polychromatic Strehl number in the working spectral range of the objective. The abscissa shows the coordinates of field points in angular measure, and the ordinate shows the Strehl number. The system has a diffraction quality in the working spectral range within the entire field of view.

The technical result achieved when solving the problem is to increase the working spectral range of the lens to 400-900 nm while maintaining a high level of correction of geometric and chromatic aberrations and small dimensions of the device.

Thus, the implementation of the technical advantages of the proposed device, which has a combination of these distinctive features, allows you to create a simple and compact design of an apochromatic objective with a relative aperture of 1:10 and good correction of chromatic and monochromatic aberrations, which can be used in telescopic systems for various purposes, including, as a lens for astronomical telescopes for visual observation.

Literature

1. Popov G.M. Modern astronomical optics. - M .: Science. Ch. ed. physical-mat. lit., 1988 .-- 192 p. P. 67-68.

2. US patent No. 785602, 1957

3. RU No. 185717, 2018

Claims (8)

Apochromatic lens, including two optically coupled components, the first component is a single-lens positive, made of Y glass, the second is a two-lens, containing a biconcave lens made of X glass and a positive meniscus, with an air gap between the components d ₁ and an air gap between the lenses the second component d ₂ , characterized in that the first component is made in the form of a biconvex lens, and the positive meniscus of the second component is made of grade Z glass, and the refractive indices and Abbe numbers of glasses X, Y and Z satisfy the following conditions: 1.7≤n _X 1.8 and 34 v _X 36; 1.6≤n _Y ≤1.7 and 51≤ν _Y ≤54, 1.6≤n _Z ≤1.7 and 30≤ν _Z ≤33, and the air gaps satisfy the conditions d ₁ ≤0.0018f, d ₂ ≤d ₁ , where n _X is the refractive index of grade X glass; n _Y is the refractive index of Y-grade glass; n _Z - refractive index of glass grade Z; ν _X is the Abbe number of grade X glass; ν _Y is the Abbe number of Y glass; ν _Z is the Abbe number of Y-grade glass; f is the focal length of the lens.

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