6m telescope

The 6-m telescope (BTA - Big Telescope Alt-azimuthal) has the status of a national instrument. SAO ensures the telescope being operative and carries out continuous work to provide BTA with modern techniques of astrophysical data accumulation and processing. The telescope is located near Mt. Pastukhova at an altitude of 2070 m above sea level, the coordinates of the site: longitude 41^o26'30", latitude +43^o 39'12".

Main mirror diameter 6 m Focal length 24 m Light collecting area 26 sq.m Wavelength range 0.3 - 10 mkm Angular resolution 0.6 arcsec - with the application of speckle   interferometry techniques 0.02 arcsec Mass of the main mirror 42 tons Total telescope mass 850 tons Telescope height 42 m Dome height 53 m Limiting stellar magnitude (1994) 26

Optical scheme of the telescope

The main mirror (MM) is parabolic in shape and has a focal length of 24 meters. The diameter of the main mirror is 605 cm, the diameter of the cilindrical prime focus cage, where optical devices and the mechanisms of input/output of the lens corrector and hyperbolic secondary focus mirror are located, is 2 m. From the laboratory tests the concentration of energy in a circle 0.8" in diameter is 90%. The image diameter is determined first of all by the microclimat in the dome and by thermal conditions of the mirror. Under favorable conditions (temperature difference between the MM, air inside the dome and outside of it) the seeing is limited by atmosphere turbulence and amounts to FWHM ~1" for 20% of observational nights.

The optical scheme of the telescope provides for working at the prime focus (f/4) and two Nasmith foci (f/30). To correct for field aberrations, when working at the prime focus, a Rosse corrector is used, which is made of K type glass (the short-wave bandwidth is 3800 ). The field of view with coma and astigmatism corrected at a level of <0.5" is about 14'. The time to switch on the beam from one focus to the other is 3-4 minutes, which makes it possible to conduct different observing programs during a night.