RU170421U1 - Optical design of an extraclock coronograph - Google Patents

Abstract

A useful model can be used to photograph plasma emissions and plasma inhomogeneities at the boundary of the chromosphere and the near corona on the limb of the Sun. The optical scheme of the extra-corona coronograph contains a lens, a light filter, an artificial moon, a field lens. In addition, a pinhole camera is installed in front of the lens, which separates the radiation of the limb part of the Sun from the total radiation flux of the solar disk and reduces the influence of harmful illumination, which is a thin metal plate with a calibrated round hole that coincides with the main optical axis of the lens. The hole diameter of the pinhole camera exceeds the radius of the lens, which is used as a single biconvex non-chromatic lens. The lens is uncorrected for longitudinal and transverse chromatic aberration, with a relative aperture value in the range D / f '= 1: 4 to 1: 7. The technical result is the achievement of opacity of the chromosphere and the near corona on the limb of the Sun with a significant field of view around the circumference of the limb. 10 ill.

Description

The utility model relates to astronomy, namely to optical instruments for studying and observing the Sun from the Earth’s surface, and can be used to photograph plasma emissions and plasma inhomogeneities at the boundary of the chromosphere and near corona on the Sun’s limb, in the visible part of the wavelengths of the Sun’s electromagnetic radiation from 3900 to 7600 Å.

A coronograph is known that contains a lens that builds the primary image, an opaque “moon” screen, a field lens, a projection lens, an aperture and a photodetector (patent SU 800946, IPC G02B 23/00, published January 30, 1981).

The disadvantage is that the optical scheme does not allow to observe the chromosphere on the limb of the Sun.

A device for observing the solar corona, consisting of a telescope, a brightness compensator and a photodetector, is known. The brightness compensator is made in the form of a combination of several compensation elements located in the working field of the input aperture. Each compensation element consists of an external eclipse disk with a diameter d located at a distance L in front of an opening with a diameter D in the entrance hatch of the telescope. The angular field Δ of the vignetted corona is determined by the relation Δ = (D + d) / 2L. It provides the expansion of the spectral range while reducing scattered light and light loss (patent No. 2226707, IPC G02B 23/00, published April 10, 2004).

The disadvantage is the limited use, namely the ability to observe the solar corona only at the time of the eclipse.

As the closest analogue, the optical scheme of the Lio coronograph was chosen, consisting of a lens, a diagonal mirror, an artificial moon, a field lens, an image transfer lens, a diaphragm, an opaque screen, and an interference filter.

http://www.old.astronomer.ru/data/library/books/sikomk/glava6/6_8.htm.

The disadvantages include the low bandwidth of the filter. In addition, for the full possibility of observing the corona of the Sun, the coronograph must be installed on a hill above the ground.

The challenge facing the author: to achieve the opacity of the chromosphere and the near corona on the limb of the Sun with a significant field of view around the circumference of the limb.

The problem is solved thanks to:

- installing a pinhole camera in front of the telescope objective;

- the use of a single biconvex non-chromatic lens as a lens, which is additionally a dispersing element.

The essence of the claimed optical scheme is the possibility of separating the radiation of the edges of the solar disk from the total radiation flux of the Sun and reducing the influence of harmful illumination, thanks to the pinhole camera additionally installed in front of the lens, which is a thin metal plate with a calibrated round hole that coincides with the main optical axis of the lens, the hole diameter of the pinhole camera exceeds the radius of the lens, which is used as a single biconvex non-achro aticheskaya lens, the lens is on uncorrected longitudinal and lateral chromatic aberration, with relative aperture value in the range D / f '= 1: 4 to 1: 7.

It is known to use pinhole cameras in astronomical instruments, for example, in X-ray and gamma-ray detectors. The chromosphere and corona of the Sun are transparent gas-plasma layers of the Sun with a lower density than the photosphere. When observations of the Sun are conducted from the surface of the Earth, it is possible to observe the chromosphere and the near corona only using special telescopes designed for these purposes.

If the pinhole camera in front of the lens of the solar telescope is not used, light from all points of the solar disk gets to any point on the outer surface of the lens. In this case, the image of the photosphere of the entire solar disk is projected in the focal plane of the lens and harmful illumination does not allow observing the chromosphere without the use of spectrographs and narrow-band light filters.

If a pinhole camera is used in front of the telescope lens, then only the peripheral part of the solar disk gets light on the outer surface of the lens closer to the edges. The images of the limb of the Sun and the central disk of the Sun obtained in the focal plane of the lens differ in orientation and intensity per unit area of the image of the Sun.

Thus, the light of the left side of the solar disk gets on the right side of the outer surface of the lens, the light of the right side of the solar disk gets on the left side of the outer surface of the lens, and so on around the entire circumference of the lens.

Using the listed properties of the pinhole camera of the lens, it is possible to isolate the radiation of the edges of the solar disk from the total radiation flux of the Sun and reduce the influence of harmful exposure.

There are similar purposes, for example, prominence spectroscope and prominence telescope, coronograph.

The composition of the optical scheme of a solar telescope-refractor

The inventive optical scheme consists of a pinhole camera 1 installed in front of the lens 2. To select two images or separate them, a light filter 3 and an artificial moon 4, or a mask, are installed. In the main focus, after the lens of field 5, there is a light detector 6.

In FIG. Figure 1 shows the optical scheme of the coronograph, which shows how a pinhole camera transmits the radiation of the limb of the Sun to the edges of the lens, so that the radiation of the central parts of the solar disk does not fall on the edges of the lens.

In FIG. Figure 2 shows the projection of the radiation of the Sun onto the outer part of the lens (A is the radiation of the entire solar disk; B is the radiation transmitted by the pinhole camera).

The method of operation of the optical scheme of a solar telescope-refractor

The pinhole camera 1, in the proposed optical scheme, is a calibrated round hole in a thin metal plate, which is installed at some distance in front of the lens 2 on the main optical axis. The plane of the plate with the pinhole hole is set perpendicular to the main optical axis of the lens 2. The center of the hole of the pinhole camera 1 coincides with the main optical axis of the lens 2. The choice of the caliber of the hole of the pinhole camera 1 and the distance of the hole to the lens 2 is the essence of the pinhole camera 1.

The gauge of the hole of the pinhole camera 1, no matter how far from lens 2, is selected so that the rays of the Sun projected by the pinhole camera 1 onto lens 2 do not reach the edge of the useful part of the aperture of lens 2.

The distance of the hole of the pinhole camera 1 to the lens 2 determines the quality indicators of the resulting image of the limb of the Sun. This distance is selected based on the practicality of the proposed telescope and the angular dimensions of the Sun. The distance of the hole of the pinhole camera 1 to the lens 2 is conveniently expressed in relation to the diameter of the lens to the distance to the hole of the pinhole camera 1 (on experimental telescopes, this ratio is selected in the range from 1:15 to 1:18). The diameter of the hole of the pinhole camera 1 exceeds the value of the radius of the lens 2.

Lens 2 builds in the main focus two images of the Sun, in the center is an inverted image of the entire disk of the Sun and, on the periphery of the image of the disk of the Sun, is a direct image of the limb part of the Sun. Lens 2 single-lens uncorrected for longitudinal and transverse chromatic aberration, to highlight several images of the Sun at different wavelengths, while the value of the relative aperture is selected in the range D / f '= 1: 4 to 1: 7

The image of the solar limb of the Sun and the central disk of the Sun obtained in the main focus differs in orientation and intensity per unit area, which allows the use of broadband filters 3 to highlight the radiation of the chromosphere and near corona on the solar limb, with a bandwidth of 200 to 1000 Å.

By selecting filters 3 and ocular lenses, which, like the lens, can be non-chromatic, some opacity of the boundary of the chromosphere and the near or inner corona of the Sun is achieved. Based on the proposed optical design, experimental telescopes were manufactured. Using these telescopes, a number of photographs of the Sun were obtained from which it is possible to evaluate the operability of the optical scheme (see explanatory materials).

The technical effect of using an optical circuit is:

- a significant field of view around the circumference of the limb of the Sun;

- comparative simplicity of optical elements;

- the possibility of manufacturing a relatively large telescope.

Thus, the task set for the author is completed.

Claims (1)

The optical scheme of an extra-coronary coronograph containing a lens, a light filter, an artificial moon, a field lens, characterized in that an obscuration camera is additionally installed in front of the lens, which emits the limb portion of the sun from the total radiation flux of the solar disk, which is a thin metal plate with a calibrated round hole, which coincides with the main optical axis of the lens, while the hole diameter of the pinhole camera exceeds the radius of the lens, which is used as a single biconvex non-chromatic lens, the lens is uncorrected for longitudinal and transverse chromatic aberration, with the value of the relative aperture in the range D / f '= 1: 4 to 1: 7.

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