RU162010U1 - OPTICAL SYSTEM WIDE-ANGLE TELESCOPE VT-78D - Google Patents

Abstract

The optical system of a wide-angle telescope containing a three-lens corrector mounted along the beam, consisting of a biconvex positive, biconcave negative and concave-convex negative spherical lenses located at a distance from each other, the main concave spherical mirror and the secondary spherical mirror deposited on the back surface are concave convex negative input corrector lenses, two spherical lenses compensating off-axis aberrations located at a distance from each other, moreover, the optical elements of the three-lens corrector and the first compensating lens along the beam are made of the same optical material of the “crown” type with a refractive index n and a dispersion coefficient v for a wavelength of 587.6 nm, satisfying the following conditions: n = 1.516 ± 0.001, v = 63.8 ± 0.1 and the second compensating lens is made of flint-type optical material with refractive index and dispersion coefficient values for the same wavelength that satisfy the following conditions: n = 1.613 ± 0.001, v = 36.9 ± 0.2, fused silica detector window, and schiysya focus flat detector.

Description

This technical solution relates to the field of astronomical instruments and can be used to create observational telescopes used to monitor near-Earth objects of artificial and natural origin, to detect supernovae and variable stars, and 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 the mirror-catadioptric systems, such as the Schmidt camera, the Maksutov system, and the Richter-Slefogt scheme, are most effective for surveillance 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 Hogton scheme is known (Haughton J.L. 1944, U.S. Patent 2,350,112), which is a modification of the Schmidt scheme. These schemes include a spherical mirror and a full-aperture three-lens corrector, which is a combination of positive and two negative thin lenses, the total optical power of which is zero, used to compensate for some aberrations and providing the possibility of increasing the back segment (distance from the last optical surface to the radiation receiver, back focal length, BFL). 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.

From the well-known modifications of the Schmidt-Hogton system, the most successful one, apparently, is the Laikin system (Milton Laikin, "Lens Design", Second edition, Marcel Dekker, Inc., New York, 1995, pp. 181-182), including an input three-lens corrector with lenses located at a distance from each other, a secondary mirror located on the rear surface of the third lens of the input corrector, as well as correcting spherical lenses located next to the focal plane, and providing an angular diameter of a flat field of view of up to 9 ° with a diameter 206.5 mm mirrors and focal distance of 254 mm. In this case, all the lenses in the optical scheme of Laikin have spherical surfaces and are made of one type of glass. The weak points of the scheme include the insufficient length of the posterior segment (5 mm), which impedes the placement of the radiation detector, and the low image quality (the rms image size in the spectral range of 0.486-0.656 μm is 19-39 μm, or 14-32 arc seconds).

The problem to which the claimed technical solution is directed is to improve the optical design of Laykin to obtain higher quality images and optimize the length of the back section.

This result is achieved by finding the optimal values of the radii of curvature and thicknesses of all lenses and the distances between them, in particular, by replacing the first in the direction of the plane convex positive lens of the input corrector with a biconvex, the second concave-convex negative lens with a biconcave, and also due to the manufacture of two small lenses of the output corrector from different grades of optical glass and their placement not closely, but at a distance from each other, which actually allows finding the theoretically best solution for Schmidt-Hogton systems. The optical elements of the three-lens corrector and the first compensating lens along the beam are made of the same optical material of the “crown” type with a refractive index n and a dispersion coefficient v satisfying the following conditions: n = 1.516 ± 0.001, v = 63.8 ± 0.1, and the second compensating lens from flint-type optical material with refractive index and dispersion coefficient values satisfying the following conditions: n = 1.613 ± 0.001, v = 36.9 ± 0.2. These changes allow us to improve the rms diameter of the images of stars in the field of view up to 5-6 microns (2.4-3.1 arc seconds) with a diameter of 250 mm and a focal length of 395 mm. In this case, the angular diameter of the planar field of view increases to 10 °, the working spectral range of the circuit expands to 0.450-0.850 μm, and the length of the rear segment increases to 40 mm, which is very important in technological and operational terms. The optical system is implemented using spherical optical surfaces and types of optical glass recommended by GOST for optical production. A version of the optical scheme using optical elements from the catalog glass of the Lytkarino Optical Glass Plant (LZOS), basic K8 and glass F1, which is part of the group of preferred types, was calculated. Other glass catalogs used in telescope engineering, in particular, the Ohara and Schott glass assortment, have varieties that are almost identical to K8 and F1, due to which the parameters of the V-78d system will not change much when replacing VLOS varieties with these close analogues. 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 detector window has zero optical power, its position, thickness, and material can noticeably change without compromising image quality, which only requires focus correction. The basic optical scheme does not include an external hood, the shape of which can be changed depending on the observation task and the detector used, and which is therefore supposed to be removable.

The technical result provided by the given set of features is to increase the quality of stellar images by 6-10 times relative to the closest analogue (Laikin optical system), increase the aperture and field of view of the telescope by more than 20%, expand the spectral range by more than two times and increase the back section, allowing you to freely install the radiation detector during operation of the telescope.

The VT-78d optical system was developed as part of applied research on the topic: “Creating a system for monitoring near-Earth objects and preventing space threats based on a new cluster of wide-angle telescopes” under the Program “Research and Development in Priority Directions for the Development of the Russian Science and Technology Complex for 2014 -2020 years, "unique identifier of applied research (project) RFMEFI60414X0099, Agreement on the provision of subsidies 14.604.21.0099.

The parameters of the VT-78d optical system are summarized in table 1. The resulting general characteristics of the telescope are presented in table 2.

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

FIG. 1 - Optical design of the VT-78d system.

FIG. 2 - Scatter plots of the VT-78d telescope in integrated light.

FIG. 3 - Integral energy distribution in the image of a point source for field angle values of 0; 1.0 °; 2.0 °; 3.0 °; 4.0 °; 5.0 °. 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 ″).

In FIG. 1 shows the proposed basic optical system of the VT-78e wide-angle telescope, containing a three-lens corrector installed along the beam, consisting of a biconvex positive (surface 1, 2), biconcave negative (3, 4) and concave-convex negative (5, 6) spherical lenses located at a distance from each other, the main concave spherical mirror (9) and the secondary spherical mirror (10) deposited on the rear surface (6) of the concave-convex negative input corrector lens. The rear side of the mirror (10) is a screen (7). Two off-axis aberration compensating spherical lenses are located at a distance from each other, and the optical elements of the three-lens corrector and the first compensating lens along the beam (surfaces 11, 12) are made of the same optical material of the “crown” type (optical glass LZ_K8 in table 1), and the second compensating lens (surfaces 13, 14) is made of optical material of the “flint” type (in table 1, optical glass LZ_F1). Further along the rays there is a fused silica detector window (surfaces 15, 16), and a flat detector (17) in focus.

LITERATURE.

Haughton J.L. 1944, U.S. Patent 2,350,112

Milton Laikin, "Lens Design", Second edition, Marcel Dekker, Inc., New York, 1995

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

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

Emelianenko VV, et al., Report on Applied Scientific Research “Creating a system for monitoring near-Earth objects and preventing space threats based on a new cluster of wide-angle telescopes. Theoretical studies of tasks assigned to PNI. Interim Report (Step 2). ” M .: Institute of Astronomy RAS, 2015

Claims (1)

The optical system of a wide-angle telescope containing a three-lens corrector mounted along the beam, consisting of a biconvex positive, biconcave negative and concave-convex negative spherical lenses located at a distance from each other, the main concave spherical mirror and the secondary spherical mirror deposited on the back surface are concave convex negative input corrector lenses, two spherical lenses compensating off-axis aberrations located at a distance from each other, moreover, the optical elements of the three-lens corrector and the first compensating lens along the beam are made of the same optical material of the “crown” type with a refractive index n and a dispersion coefficient v for a wavelength of 587.6 nm, satisfying the following conditions: n = 1.516 ± 0.001, v = 63.8 ± 0.1 and the second compensating lens is made of flint-type optical material with refractive index and dispersion coefficient values for the same wavelength that satisfy the following conditions: n = 1.613 ± 0.001, v = 36.9 ± 0.2, fused silica detector window, and schiysya focus flat detector.

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