RU192789U1 - FOUR-LENS APOCHROMATIC LENS - Google Patents

Abstract

The lens can be used in telescopic systems, including astronomical telescopes for visual observation. The lens contains two components separated by an air gap d. The first component contains biconvex and biconcave lenses made of two grades of glasses Y and X, respectively, and separated by an air gap d, and the second contains a biconvex lens and a negative meniscus separated by an air gap d. The relations are satisfied: 1.6≤n≤1.7 and 49≤ν≤55; 1.5≤n≤1.7 and 51≤ν≤66, d≤0.002f; d≤d, d≤d, where n is the refractive index of glass grade X; n is the refractive index of glass brand Y; ν is the Abbe number of glass grade X; ν is the Abbe number of Y-grade glass; f is the focal length of the lens. The technical result is the creation of a simple and compact design with an increased relative aperture (up to 1: 6) and a reduced overall length of the device while maintaining good correction of geometric and chromatic aberrations. 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.

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) values of the air gaps between the components, which leads to a complication of the design and instability of the relative position of the components during operation.

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) is of three [R.ChristeninSkyandTelescope (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 thin superachromat from 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 glasses, 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.

Known four-lens apochromat, consisting of a meniscus lens facing a concave surface to an object, a biconcave lens and two biconvex lenses [Slyusarev G.G. "Calculation of optical systems", L-d, Engineering, 1975, 640 S. Page 114-116]. For the manufacture of lenses, three different optical materials are used, including a “special” flint.

The disadvantages of this lens are the use of three brands of glass, including an expensive “special” flint, a low (1:10) relative aperture of the lens, and a large residual chromaticity of the position in the blue region of the spectrum.

The closest technical solution adopted for the prototype is a two-component apochromatic lens [RF patent for utility model No. 185717 of 09/11/2018. Two-component apochromatic lens], including two optically coupled components separated by an air gap of d ₁ , the first component contains one positive lens made of brand Y glass; the second contains two lenses: a biconcave made of brand X glass and a positive meniscus made of brand Y glass separated by an air gap 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,

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 disadvantages of this lens are the low (1:10) relative aperture and, as a result, the large overall length of the device, as well as the presence of optical surfaces with high curvature in the lens.

The technical solution is aimed at creating an apochromatic lens of a simple and compact design with an increased relative aperture of 1: 6 and a reduced overall length of the device.

The technical result is achieved by the fact that a four-lens apochromatic lens is proposed, including two optically coupled components separated by an air gap d ₂ , characterized in that the first component is double-lens and contains biconvex and biconcave lenses made of two grades of glasses Y and X, respectively, and separated by air a gap d _1, the second - bi-convex lens and a negative meniscus made, as in the prior art of glass marks Y and X, respectively, separated by an air spacing d m _3, than the air gap satisfy the following conditions:

d ₂ ≤0.002f,

d ₁ <d ₂ and d ₃ <d ₂ .

The four-lens apochromatic lens shown in FIG. 1 consists of two components: the first component contains a biconvex lens 1 made of grade Y glass and a biconcave lens 2 made of grade X glass, the second contains a biconvex lens 3 made of grade Y glass and a negative meniscus 4 made of grade X glass The first component is separated from the second by an air gap d ₂ , and the lenses inside the components are separated by air gaps d ₁ (lenses 1 and 2) and d ₃ (lenses 3 and 4).

Air gaps d ₁ and d ₃ are used to correct for spherical aberration, and the space d ₂ is used to correct spherochromatic aberration. 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,

and the air gaps are such that:

d ₃ ≤0.002f;

d2, d ₁ ≤d ₃ ,

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;

All optical surfaces are spherical in shape.

The action 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 lens with a diameter of 102 mm, which coincides with the first surface, and, having refracted successively through the surfaces of four lenses, 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:

Focal length F '- 612 mm

Relative aperture - 1: 6

The working spectral range of the lens is 0.479 ÷ 0.656 μm

Angular field in the space of objects - +/- 0.3 °

Refractive index n _d glass X - 1,743

The number of Abbe ν _d glass X - 49.95

Refractive index n _d glass Y - 1,622

The Abbe number _{d of the} glass Y is 56.63

The design parameters of the calculated lens are shown in table 1. The lines “1”, “2”, “3” and “4” indicate the radii of curvature, thickness, refractive index and Abbe number for four lenses. The lines "d ₁ ""d ₃ " indicate the air spaces between the lenses 1-2 and 3-4, respectively, and in the line "d ₂ " - the air gap between the components.

The high quality of the image created by the proposed four-lens 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 shown for the spectral range F '- C. The longitudinal chromatic aberration in microns is plotted on the abscissa, and the wavelength in nanometers is plotted on the ordinate. The S-shaped nature of the curve of longitudinal chromatic aberration is clearly visible, which indicates that in the proposed lens in the specified spectral range, three wavelengths are brought together in one focus and thereby a high degree of correction of chromatic aberration is achieved, the value of which in this example is 42.29 microns, which is 1/14550 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 on the ordinate axis. The system has diffraction quality in the working spectral range within the entire field of view.

The technical result achieved by solving the problem lies in increasing the relative aperture of the lens to 1: 6 while maintaining the values of air gaps within 0.002f, which also reduced the overall length of the device.

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 a high relative aperture and good correction of chromatic and monochromatic aberrations, which can be used in telescopic systems for various purposes, including, as lens of astronomical telescopes for visual observation.

Claims (12)

A four-lens apochromatic lens including two optically coupled components separated by an air gap d ₂ , characterized in that the first component is made of two-lens and contains biconvex and biconcave lenses made of two grades of glasses Y and X, respectively, and separated by an air gap d ₁ , the second two a convex lens and a negative meniscus, separated by an air gap of d ₃ , the refractive indices and the Abbe numbers of the glasses X and Y are such that: 1.6≤n _X ≤1.7 and 49≤ν _X ≤55; 1.5≤n _Y ≤1.7 and 51≤ν _Y ≤66, and air gaps satisfy the following conditions: d ₃ ≤0.002f; d ₂ ≤d ₃ , d ₁ ≤d ₃ , 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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