RU152320U1 - OPTICAL SYSTEM WIDE-ANGLE TELESCOPE VT-72E - Google Patents

Abstract

The optical system of a wide-angle telescope containing a two-lens corrector installed along the beam, consisting of positive and negative spherical lenses located at a distance from each other, the main concave spherical mirror and a secondary spherical mirror deposited on the surface of the negative lens, three spherical compensating off-axis lens aberrations, the first two of which are distant from each other, and the third is located close to the second, plane-parallel filter, fused silica detector window, and the detector in focus, as well as a system for eliminating direct illumination of the detector, containing a set of diaphragms located in a hood 290 mm long, counting from the top of the first lens, and covering a conical beam of useful light, providing a telescope field of view.

Description

Wide-angle telescope optical system VT-72e

This technical solution relates to the field of astronomical instruments and can be used for the serial creation of observational telescopes that serve to monitor near-Earth objects of artificial and natural origin, to detect supernovae and variable stars, a number of other important astronomical tasks that require frequent updating of information for wide observational areas.

Modern optical telescopes make it possible to obtain more detailed images of objects than their predecessors, in particular, the “atmospheric barrier” of image quality is overcome. A class of wide-angle optical telescopes that provide image quality no worse than one second of arc within the field of view of at least one angle of degree is designed to detect objects of variable brightness in the sky and conduct survey work. A number of optical schemes are known from the prior art, of which mirror-lens (catadioptric) systems, such as the Schmidt camera, the Maksutov system, and the Richter-Slefogt scheme, have the highest efficiency for survey tasks. Since chromatic aberration increases rapidly with increasing optical power of the lenses, it is desirable that the lens component be as close to the afocal system as possible, that is, have the largest effective focal length. Thus, it is desirable to assign power functions to mirror elements, while the main purpose of close to afocal lens optics is to eliminate monochromatic aberrations of the system, if possible without introducing intrinsic chromatism. The following Richter-Slefogt scheme is known (R. Richter, N. Slevogt, German Patent Application 1941, No. Z 26592 IXa 42h.), Which is a modification of the Schmidt scheme. This scheme includes a spherical mirror and an afocal two-lens corrector, which is a close doublet of positive and negative thin lenses, the total optical power of which is zero, used to compensate for some aberrations. This system, however, is not sufficiently wide-angle due to the chromatism of the increase at large field angles, due to the dependence of the coefficient of increase of the system on the wavelength.

A larger angular field is achieved in the optical system of the TTM telescope described in Tarasenko I., Terebizh V., Markelov S. "Some Issues of Creation of Wide-Field Telescopes for Monitoring Satellites and Space Debris in High Earth Orbits", 8th US / Russian Space Surveiiance Workshop, Maui, Hawaii, April 18-23, 2010. This scheme includes an input two-lens corrector with lenses spaced apart from each other, a secondary mirror located on the rear surface of the second lens of the input corrector, as well as corrective spherical lenses located next to the focal plane. Moreover, the elements included in the system have spherical surfaces, which reduces the complexity of manufacturing and the cost of the system. This optical system provides a mean-square diameter of stellar images over the field of view from 12 μm to 17 μm (1.8-2.5 arc seconds), the diameter of a circle covering 80% of the energy in the star image is for the ТТМ 2.6 ″ -4.0 ″.

The problem to which the claimed technical solution is directed is to improve the optical scheme of the TTM to obtain higher quality images.

This result is achieved by adding a third, negative, lens to the output corrector, when placed close to the second. This allows us to improve the mean square diameter of the images of stars in the field of view to 4.5-6.8 μm (1.1 ″ -1.6 ″), while the diameter of the circle, covering 80% of the energy in the image of the star, is 2.0 ″ -2.7 ″. In addition, the described change in the optical system makes it possible to approximately double the rear segment of the system (distance from the last optical surface to the radiation receiver, back focal length, BFL) and move the image plane away from the main mirror by the same amount; These features are very important in technological and operational terms. The optical system is implemented using spherical optical surfaces with radii of curvature from the list of GOST 1807-75 and the types of optical glass recommended by GOST for optical production. The diameter of the central hole in the main mirror can be arbitrarily selected in the range of 120-160 mm without introducing additional light vignetting into the system. It is assumed that one of the currently available CCD arrays with a diagonal of ~ 52 mm and a pixel size of 9 or 12 μm can serve as a radiation receiver. A version of the optical scheme with an aperture of 400 mm was calculated provided that optical elements were made of glass from the catalog of the Lytkarino Optical Glass Plant (LZOS), and the most common optical curvature radii were selected

surfaces from the list of GOST 1807-75, which allows to significantly simplify and reduce the cost of manufacturing the optical system, as well as alternative versions using the range of glasses from Ohara and Schott. The main characteristics of the system are common to all three versions. The material of the detector window is usually fused silica; the calculations were based on Fused Silica material from the ZEMAX MISC or INFRARED catalogs. However, since the filter and the detector window have zero optical power, their position, thickness and material can noticeably change without compromising image quality. Verification showed that in the optical system there are no dangerous glare due to double reflection of light from optical surfaces.

With the field of view, which is provided by the VT-72e telescope, almost the entire space between the primary and secondary mirrors is filled with light beams from objects, therefore, the commonly used internal direct light cutoffs in the form of truncated cones are not applicable, since they would introduce an undesirably large screening of useful light. Elimination of direct illumination of the detector is achieved by placing a set of diaphragms in a hood with a length of 290 mm, counting from the top of the first lens. The diaphragms cover a conical beam of useful light, providing a field of view of 3.5 °. The inner surface of the hood should be made porous. The diameter of the light beam near the first lens of the light corrector is only 15 mm larger than the light diameter of 115.6 mm of this lens.

The technical result provided by the given set of features is to increase the quality of stellar images by 1.5 times relative to the closest analogue (optical system ТТМ), while achieving a quality close to diffraction (3.5 ° at an aperture of 400 mm), lengthening the back section by half, simplifying and cheaper manufacturing of the optical system, compact telescope, low requirements for grades of glass, lack of aspherical surfaces and soft tolerances.

The parameters of the VT-72e optical system are summarized in Table 1. The characteristics of the diaphragms placed in the hood to eliminate direct exposure to the detector are shown in Table 2. The resulting general characteristics of the telescope are presented in Table 3.

1) All surfaces are spheres. The numbering of surfaces corresponds to the course of the rays.

2) Aperture diaphragm.

3) The diameter of the central hole in the main mirror is selected in the range of 120-160 mm.

4) A secondary mirror is applied to surface No. 4.

5) Fused Silica - fused silica.

The VT-72e system is resistant to replacing LZOS glass types with the corresponding Ohara catalog brands. The radii of all optical surfaces and the thickness of the lenses remain the same; changes are reduced to replacements listed in table. four.

The system can also be implemented using glass grades manufactured by Schott. All radii remain the same, the changes concern only two lenses of the output corrector (Table 5).

The proposed utility model is illustrated by the following graphic materials:

FIG. 1 - Optical design of the VT-72e system.

FIG. 2 - Scatter plots of the VT-72e telescope in integrated light.

FIG. 3 - Integral energy distribution in the image of a point source for field angle values of 0; 0.5 °; 1.0 °; 1.25 °; 1.5 °; 1.75 °. At the top of each square is the field angle of the point source, and at the bottom are the coordinates of the image on the detector. The side of the square corresponds to 12 μm (2.9 ").

FIG. 4 - The proportion of non-vignette rays depending on the field angle.

FIG. 5 - The path of the rays in a telescope equipped with a hood and a system of input diaphragms. The numbers of the diaphragms are given in table. 2.

In FIG. 1 shows the proposed optical system of the VT-72e wide-angle telescope. The system contains a two-lens corrector installed along the beam, consisting of positive (surface 1, 2) and negative (3, 4) spherical lenses made of the same glass (in table 1 LZ_K8 LZOS) and located at a distance from each other , the main concave spherical mirror (5) and the secondary spherical mirror (6) deposited on the surface of the negative lens (4), three spherical compensating off-axis lens aberrations (surfaces 7 and 8, 9, 10, 11 and 12) immediately before the focus, two the first of which are removed from each other made of glass of a different grade (in table 1 LZ_T16 LZOS), and the third is located close to the second and made of glass of the same grade as the lenses (1,2) and (3,4), plane-parallel filter (surfaces 13 and 14) of the same material (LZ_K8), a fused silica detector window (surfaces 15 and 16) and a detector (17). The rays of light pass through the two-lens corrector (1,2) and (3,4), reflected from the main mirror 5 and the secondary mirror 6 deposited on the surface 4 of the corrector lenses, and are collected by the lenses (7,8), (9,10) and (11,12) of the off-axis aberration compensator in the image plane of the telescope at a small distance behind the compensator.

In FIG. 5 shows a technique for eliminating direct exposure to the detector, avoiding undesirably large shielding of useful light when using the VT-72e optical circuit. This goal is achieved by placing a set of diaphragms (18-21) in a hood 290 mm long, counting from the top of the first lens. The diaphragms cover a conical beam of useful light, providing a field of view of 3.5 °.

LITERATURE.

R. Richter, N. Slevogt, German Patent Application 1941, No. Z 26592 IXa 42h

Tarasenko I., Terebizh V., Markelov S. "Some Issues of Creation of Wide-Field Telescopes for Monitoring Satellites and Space Debris in High Earth Orbits", 8th US / Russian Space Surveiiance Workshop, Maui, Hawaii, April 18-23, 2010 .

V.Yu. Terebizh, "Modern optical telescopes." M .: Fizmatlit, 2005.

V. Terebizh, "New designs of survey telescopes", 2011, Astronomische Nachrichten 332, iss. 7, p. 714.

Claims (1)

The optical system of a wide-angle telescope containing a two-lens corrector mounted along the beam, consisting of positive and negative spherical lenses spaced apart, the main concave spherical mirror and a secondary spherical mirror deposited on the surface of the negative lens, three spherical compensating off-axis lens aberrations, the first two of which are distant from each other, and the third is located close to the second, plane-parallel filter, fused silica detector window, and the detector in focus, as well as a system for eliminating direct illumination of the detector, containing a set of diaphragms located in a hood 290 mm long, counting from the top of the first lens, and covering a conical beam of useful light, providing a telescope field of view.

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