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Russian-Turkish 1.5-m Telescope

High energy Astrophysics department of IKI, Moscow
International astrophysical observatory Spectrum-X-Gamma
International astrophysical space observatory INTEGRAL

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1:48 Coude optical scheme

The primary mirror 1 reflects light to the secondary mirror 2 which sends the converging beam of light to the system of four flat mirrors 3, 4, 5 and 6. That allows the beam of light to leave the telescope strictly along its polar axis and be collected in Coude focus. Mirror 3 is fixed relative to tube and is placed at the crossing point of main optical axis of telescope and declination axis. That's why at any tube position (for any rotation along the declination axis) beam of light parallel to the principal axis after reflection on mirror 3 follows the direction of declination axis. Similarly, mirrors 4, 5 and 6 are fixed within the yoke, hense the beam that was originally parallel to the optical axis of telescope becomes parallel to the polar axis upon reflecting from mirror 6. This design provides the main feature of Coude focus - its fixed position. That is, at any pointing of telescope tube and mount the image of object at the optical axis of the instrument will be at Coude focus independent of telescope rotation during the guiding. This focus usually serves for installing the bulky instruments, for example spectrometers which require of strict thermal stability and absence of mechanical deformations. Since the mount is rotating along the hour axis during the guiding, the image in Coude focus will also rotate at the same speed, i.e. 1 revolution per day, or 15o/hour.

Focal length, mm
Linear field of view, mm
Angular field of view
Central screening area, %
Concentration of light energy at 632.8 nm wavelength
on the optical axis within the circles of diameter:
0.108 mm, %, at least
0.180 mm, %, at least