RTT150
Russian-Turkish 1.5-m Telescope

International astrophysical space observatory INTEGRAL

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HEAD IKI

Telescope's optical systems

Telescope has two main foci (Cassegrain and Coude) and allows to use six optical systems based on Ritchey-Chretien system with a common main mirror. At present scientific observations are being performed at the Cassegrain focus in main optical scheme with focal ratio of 1:7.7. Other optical schemes may be used with developing new focal instruments. All optical schemes of telescope are designed to work in the spectral range of wavelengths 325 nm < l < 1000 nm.

**Summary of RTT150 optical schemes**
Scheme	Equivalent focal length	Angular field of view	Linear field of view	Image scale	Central screening in area	Shape of focal surface
1:3 with Meinel camera	4519 mm	1^o	79 mm	45".6/mm	25.8%	flat
1:7.7 with corrector	11639 mm	1^o28'	300 mm	17".6/mm	25.8%	flat
1:7.7 without corrector	11611 mm	26'40"	90 mm	17".8/mm	25.8%	sphere
1:17.3 with corrector	26007 mm	13'	100 mm	7".8/mm	17%	flat
1:16 without corrector	24029 mm	4'18"	30 mm	8".6/mm	11.6%	sphere
1:48, Coude	72257 mm	3'50"	80 mm	2".9/mm	17 %	sphere

The needed optical scheme is achieved by installing appropriate secondary hyperbolic mirror, blends and correcting lenses (if they are used in a given scheme). To use the Coude focus the removable flat diagonal mirror is also needed in the crossing point of declination axis and main optical axis of telescope. This mirror reflects the converging beam of light to the system of 3 mirrors placed inside the base yoke and after reflecting from the latter of them light is going downwards along the polar axis.

Replacment of secondary hyperbolic mirrors is performed at the tube of telescope in horizontal position using the dome crane. To protect the gear of declination axis from hits and shakes during the change of secondary mirrors or during removal/installation of main mirror cell, the yoke base with declination axis drive has fixing element which allows to hold the telescope tube in horizontal and vertical positions.

All drives, both on hour and declinations axis, are placed in the base. To protect the telescope from the possible seismic affects the couplings are provisioned which fix the telescope mount.