RU185717U1 - TWO COMPONENT APOCHROMATIC LENS - Google Patents

Abstract

The lens can be used in telescopic systems, including astronomical ones for visual observation. The apochromatic lens contains two components separated by an air gap d ₁ . The first component contains one positive lens made of brand Y glass, the second contains a biconcave lens made of brand X glass, and a positive meniscus made of brand Y glass, separated by an air gap of d ₂ . The 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 glass grade X; n _Y is the refractive index of glass of brand Y; ν _X is the Abbe number of glass grade X; ν _Y is the Abbe number of glass of grade Y; f is the focal length of the lens. The technical result is the provision of a simple and compact design with high correction of chromatic and monochromatic aberrations and an increased relative aperture. 3 ill., 1 tab.

Description

The utility model relates to the field of optical instrumentation and can be used as an apochromatic lens for telescopic systems for various purposes, including astronomical telescopes for visual observation.

A known refractor system with an apochromatic corrector containing two components, the first of which (the lens) is made of two lenses, and the second (corrector) of three [R. Christen in Sky and Telescope (Oct., 1985), pp. 375-378].

The disadvantages of this system are the large (1/3 of the focal length) air gap between the lens and the corrector, the use of glass with a special dispersion course in the corrector, and the residual chromaticity of the increase.

Known apochromatic lens, consisting of three components [RF Patent No. 2429508, 2010. Apochromatic lens], the first and third of them are positive, and the second is negative. Lenses are made of two brands of optical glasses.

The disadvantages of this lens are large (of the order of the focal length of the lens) air gap between the components, which leads to a complication of the design and instability of the relative position of the components during operation.

Known three-lens two-component apochromatic lens Kohler (Kohler) [US patent No. 785602, 1957.]. The lens consists of two components separated by an air gap. The first component along the rays consists of one positive lens, and the second consists of positive and negative lenses glued together. The air gap between the components is 2-6% of the focal length of the lens. The first positive lens along the rays has a refractive index for the d line greater than 1.6 and an Abbe number greater than 55, and the lenses of the second component have an Abbe number less than 35, a relative partial dispersion difference of more than 1.61, and a difference of refractive index of less than 0.1. In this case, the difference in the refractive indices of the lenses of the second component and the lens of the first component should be greater than OD. The Kekhler lens allows you to get a good quality correction of geometric aberrations and the correction of the chromaticity of the position for three wavelengths only with relative openings not higher than 1:12 (with an entrance pupil diameter of 102 mm).

The disadvantages of this lens are the use of three brands of glasses, two of which are expensive heavy flints, including lanthanum flint, gluing, which limits the diameters of the lenses to be glued, strict requirements for the optical constants of the glasses, which limits the designer in choosing glasses, insufficient correction spherochromatism in the blue region of the spectrum.

The closest technical solution adopted for the prototype is a thin super-chromatograph of three lenses [Popov G.M. Modern astronomical optics. - M .: Science. Ch. ed. Phys.-Math. Lit., 1988 .-- 192 p. Page 62-68], consisting of two positive and one negative lens. One positive and one negative lens are glued, and the second positive lens is separated from the gluing by the air gap. For the manufacture of lenses, three different optical materials are used, including “special” glasses and fluorite.

The disadvantages of this lens are the use of three brands of glass, including expensive and low-tech “special” glasses and fluorite, gluing, low (1:15) relative apertures of lenses that use only “normal” glasses. With such relative holes, the device has a significant overall length.

The technical solution is aimed at creating an apochromatic lens of a simple and compact design with high correction of chromatic and monochromatic aberrations and an increased relative aperture.

The technical result is achieved in that in the bicomponent apochromatic lens comprising two optically coupled component separated by an air gap d _1, the first component comprises one positive lens made of a glass marks Y, the second - biconcave lens made of glass mark X and a positive meniscus, made of glass of brand Y, separated by an air gap of d ₂ , the 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 glass grade X;

n _Y is the refractive index of glass of brand Y;

ν _X is the Abbe number of glass grade X;

ν _Y is the Abbe number of glass of grade Y;

f is the focal length of the lens:

The properties of the materials from which the lenses were made were selected by software methods in such a way as to achieve maximum correction of longitudinal chromatism. Air gaps d ₁ and d ₂ between the components of the lens are used to correct spherical and spherochromatic aberrations, respectively.

The apochromatic lens shown in FIG. 1 contains two components: the first component contains one positive lens 1 made of grade Y glass, the second contains a biconcave lens 2 made of grade X glass and the positive meniscus 3 made of grade Y glass. The first component is separated from the second by an air gap d ₁ . In the second component, the lenses 2 and 3 are separated by an air gap d ₂ .

The action of the lens shown in FIG. 1. carried out as follows: a parallel beam of rays from a distant object passes sequentially the first and second components and builds an image of this object in the focal plane F '.

The following is an example of a specific implementation of the proposed lens.

The following lens is calculated as an example:

The refractive index n of the glass X is 1.744; the Abbe number v of the glass X is 50.26; the refractive index n of the glass Y is 1.572; the Abbe number ν of the glass Y is 57.33; focal length F '- 990 mm; relative aperture - 1:10; the working spectral range of the lens is 0.434 ÷ 0.700 microns; the main wavelength is 0.587 microns; angular field in the space of objects - +/- 0.25 °

The design parameters of the calculated lens are shown in table 1. The lines “1”, “2”, “3” indicate the radii of curvature, thickness, refractive index, and Abbe number for the yellow helium line d for three lenses. The lines “d ₁ ” and “d ₂ ” indicate the air spaces between the lenses.

The high quality of the image provided by the proposed optical system of a two-component apochromatic lens is confirmed by the graphic materials presented in FIG. 2 and FIG. 3.

In FIG. 2. A graph of longitudinal chromatic aberration is given for the spectral range from 0.434 μm to 0.700 μm. The horizontal chromatic aberration in microns is plotted on the abscissa, and the wavelength in nm is plotted on the ordinate. The W-shaped nature of the curve of longitudinal chromatic aberration is clearly visible, which indicates that in the proposed lens in the specified spectral range, the four wavelengths are brought together in one focus and thereby achieved a high degree of correction of chromatic aberration, the value of which in this example is 78.8 microns, which is 1/12563 of the magnitude of the focal length of the lens.

In FIG. 3. shows a graph of the polychromatic Strehl number in the working spectral range of the lens. The coordinates of the field points in the angular measure are plotted along the abscissa axis, and the Strehl number along the ordinates. The system has diffraction quality in the spectral range of 0.434-0.700 μm within the entire field of view.

The technical result achieved in solving the problem lies in increasing the relative aperture of the lens (up to 1: 10-1: 8) and reducing the air gaps between the components (up to 0.005ƒ), which reduced the overall length of the device, using only lens materials two grades of glass - crowns with a normal dispersion course, which increases the manufacturability of the design and reduces the cost of the lens and in improving the correction of aberrations in a wide spectral range of 0.434-0.700 microns due to the selection of the dispersion properties of optical Sgiach materials and optimization of the design parameters of the circuit.

Thus, the implementation of the technical advantages of the proposed device, which has a combination of these distinguishing features, allows you to create a simple and compact design apochromatic lens with high correction of chromatic and monochromatic aberrations, which can be used as a lens in astronomical telescopes for visual observation.

Literature

1. Popov G.M. Modern astronomical optics. - M .: Science. Ch. ed. Phys.-Math. Lit., 1988 .-- 192 p. Page 62-68.

2. A. Rogers "On the Construction of large Achromatic Telescopes", Memoirs of the Astronomical Society of London 3.2 (1829), pp. 375-378.

3. R. Christen in Sky and Telescope (Oct., 1985), pp. 375-378.

4. US patent No. 785602, 1957.

5. RF patent No. 2429508, 2010. Apochromatic lens.

Claims (10)

A two-component apochromatic lens, comprising two optically coupled components separated by an air gap d ₁ , characterized in that the first component contains one positive lens made of brand Y glass, the second a biconcave lens made of brand X glass and a positive meniscus made of glasses of brand Y, separated by an air gap of d ₂ , the 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 glass grade X; n _Y is the refractive index of glass of brand Y; ν _X is the Abbe number of glass grade X; ν _Y is the Abbe number of glass of grade Y; f is the focal length of the lens.

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