Schiefspiegler
As Schiefspiegler be reflecting telescopes referred to in which the secondary mirror (secondary mirror) in the optical axis of the primary mirror is located and the beam path through the tilted mirror is inclined by a few degrees.
The purpose of the construction is to avoid that the secondary mirror part of the main mirror shades , as in all classic systems with the exception of Herschel -Teleskops is the case. This on the one hand eliminates this slight loss of light, but above all, there is no disruptive diffraction on the secondary mirror and its holder.
The imaging errors (astigmatism and coma) that occur during tilting can be reduced by designing the optics with a long focal length and largely compensated for by optical correction on the secondary mirror or a correction plate. A small disadvantage is that the tube has to be partially open because of the inclined beam path. This can lead to local air turbulence and temporary image flickering.
The modern design (cutter) Schiefspiegler was developed in the 1930s by the German mechanical engineer Anton Kutter , after a previous design had been built in 1877 by the Austrian opticians J. Forster and K. Fritsch .
There are other modern Schiefspiegler constructions with different mirror tilting and spherical mirrors or a second or third auxiliary mirror . Please refer
- Brachyte telescope (Forster / Fritsch 1877)
- Kutter-Schiefspiegler - better known in Europe - and
- Yolo-Schiefspiegler - preferred by amateur astronomers in the United States
- A family of modern two-mirror Schiefspiegler after Richard F. Horton, derived from the Cassegrain, with f / 5 to f / 16,
- Tri-Schiefspiegler with three mirrors, designs by Anton Kutter, Arthur S. Leonard (Solano), Richard A. Buchroeder and David Stevick (Stevick-Paul telescope), as well
- Tetra-Schiefspiegler with four mirrors or optically effective mirror surfaces (Brunn, Herrig, Wolter).
All Schiefspiegler are next to the o. A. Advantages higher in contrast than the classic types of mirror telescopes , but also more complex to manufacture. Therefore, they are mostly made in-house by mechanically experienced mirror grinders , for which some astro clubs offer special building instructions (see also Amateur Telescope Making ).
For only one optically effective mirror, a tilted parabolic mirror, R. V. Willstrop and later independently Ed Jones developed a near-focus corrector using a tilted arrangement of a planoconvex and a planoconcave lens and referred to it as a chief mirror , a play on words from "Catadioptric Herschellian oblique mirror".
The Herrig-Schiefspiegler, which consists of a convex and a concave spherical mirror, has a particularly simple structure with very good imaging properties. These are run through twice, which minimizes imaging errors and results in an image field of 0.4 °. Disadvantages of the construction are the mirrors, which have a diameter of approximately one and a half times the aperture, and the large radii of the mirror surface that are difficult to produce. In a variant with a two-part mirror for the first and third reflection, it is commercially available as a Wolterscope.
Richard Buchroeder designed a Tri-Schiefspiegler, which consists of three spherical surfaces and achieves a diffraction-limited image also for a field of view of 0.4 °.
David Stevick developed a particularly well corrected Tri-Schiefspiegler in 1991, who rediscovered the principle of the Paul corrector and avoids its large obstruction by performing as a Schiefspiegler. This design, which consists of a parabolic mirror, a convex and a concave spherical mirror, the latter having the same radii of curvature, is therefore called the Stevick-Paul telescope. Although the focus is more accessible than with a Paul corrector, a fourth, flat mirror is required for observation with an eyepiece, which folds the beam path outwards.
Other well-corrected tetra oblique mirrors with external focus were developed by Michael Brunn in 1989, using either three spherical and one plane deflecting mirror or one ellipsoidal main mirror and three spherical mirrors. For the latter, openings up to about 1 m are planned.
Outside of the amateur field, tilted mirror arrangements are still rarely used. Early examples are the Herschel telescope and the Leviathan , built according to the same principle , which used the principle to construct a telescope with just one mirror, since the metal mirrors available in the 18th and 19th centuries had a low reflectivity. Brachyt-Schiefspiegler by Forster / Fritsch were sold around 1900 and a copy with a 32 cm opening was installed in the Pola observatory . The principle is modernly used in the astrometry space probe Gaia in order to achieve compact dimensions. The principle was also examined to expand the field of view of Liquid-Mirror Zenith telescopes .
Two new US solar telescopes take advantage of the obstruction-free Schiefspiegler technology, the 1.6 m Goode Solar Telescope (GST) of the Big Bear Solar Observatory (BBSO) in Big Bear Lake in the San Bernardino Mountains, about 120 km east of Los Angeles , as well as the world's largest solar telescope with its 4 m primary mirror, the Daniel K. Inouye Solar Telescope (DKIST) near Kula on Maui / Hawaii , which will go into operation in 2020 .
credentials
- ^ RV Willstrop: A simple coma corrector for off-axis guiding , 1980MNRAS.191..777W
- ↑ Ed Jones: Chief Speigler. April 25, 2015. Retrieved August 14, 2016 (American English).
- ↑ Erwin Herrig: Kompakt-Schiefspiegler (mirror telescope) , 1996
- ↑ a b c d Herbert Gross, Fritz Blechinger, Bertram Achtner: Handbook of Optical Systems: Survey of optical instruments , Wiley-VCH Verlag, 2008
- ↑ Wolter Scope
- ^ Tilted Component Telescope
- ↑ The Stevick-Paul Telescope ( Memento of the original from August 24, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ Michael Brunn: Mirror system free of silhouette for astronomical telescopes of the Schiefspiegler type
- ^ Karl Fritsch: Illustrirtes price list of astronomical and optical instruments , Vienna, 1882
