RTT150
Russian-Turkish 1.5-m Telescope

International astrophysical space observatory INTEGRAL

(C) Copyright
HEAD IKI

Guides and finders

RTT150 telescope is equipped with two guides - photoelectric and visual ones which are attached to the telescope tube from opposite sides, symmetrically relative to the declination axis. Each guide has its own finder.

Photoelectric guide

Photoelectric guide consists of tube and photoelectric head.

Guide is built on Cassegrain optical scheme. The main mirror 1 reflects light to the secondary mirror 2 which collects it in the focal plane of system. To improve image quality lens corrector 3 is placed between focal plane and secondary mirror. Blends A, B and C fully remove dispersed light. The system is thermally stable due to usage of quartz as a material for optical parts and thermally stable connection based on invar. That allows to maintain the constant air volume between primary and secondary mirror during the daily and season temperature changes at the observatory.

Guide characteristics
Primary mirror diameter, mm	359
Focal length, mm	3590
Focal ratio	1:10
Linear field of view, mm	80
Angular field of view	1^o16'
Central screening area, %	34
Concentration of light energy at 632.8 nm wavelength on the optical axis within the circle of diameter
0.036 mm, %, at least	81
The same at the edge of field of view, at 40 mm from optcal axis within the circle of diameter
0.036 mm, %, at least	81

The tube has a blend at the front side which is attached to it with the aid of hinge and shutter. It can be moved aside during the changing the secondary mirrors of the telescope. Blend has the door with electro-mechanical drive which is operated from the telescope control station.

Photoelectric head includes modulator, block of photoamplifier and optical-mechanical system represented by narrow field (2mm) lense placed on two slides for its motion within guide FOV. Slides motion directions are mutually perpendicular, X axis corresponding to image motion along hour angle (right ascension) and Y axis - along declination.

Range of narrow-field lens motion along X and Y axes covers +/-40 mm from the average value that corresponds to the position of photoguide line of sight parallel to the telescope line of sight. X and Y slides have optical rulers with 1 mm step and raster grids which provide 0.01 mm readout accuracy. Kellner eyepiece with focal length of 56 mm is placed at the outer side of the focal part of photoguide. Guide star and central cross can be seen through this eyepiece. The second eyepiece with 28 mm focal length is also available for X and Y values readout. For the observer's convenience position of this eyepiece can be changed using the optical knuckle.

Control of X and Y slides motion is provided by the special key from the tools set. The plug connector for it is located at the photohead.

Besides that, the assembly carries the following items:

Switch for changing the position of diagonal mirror from V (visual guiding) to PH (photoelectric guiding).
Two toggles for switching the light in central cross of eyepiece and readout scales of X and Y slides motion.
Two rheostats for adjusting the illumation level of X and Y readout scales and that of eyepiece grid.
Plug connector for photoguide - telescope control system cable.

Visual guide

Visual guide consists of a tube analogous to that of photoelectric guide and micrometric eyepiece.

Micrometric eyepiece has the following parameters:
Limits of eyepiece motion from the average position, mm:
along X axis	+/-40
along Y axis	+/-40
Accuracy of eyepiece motion readout with the grid in the system, mm	0.01
Focal lengths of interchangeable eyepieces, mm	10, 20, 28, 40, 56
Power voltage, V	27

The motion of eyepiece with grid is performed with the aid of two flywheels over two mutually perpendicular directions designated as X and Y in the field of readout system. Illumination of eyepiece grid is switched on by two toggles, brightness of light can be adjusted by two rheostats placed near flywheels.

The moving part of micrometric eyepiece can be rotated by any angle around the axis of visual guide with the aid of positional bearing. To readout rotation angle the scale with 1^o step and 1' nonius are available. To fix the needed angle there is a clamp with holder under the scale of position angles.

Finder

A-319 finder is a telescopic spyglass. Due to a small (20x) magnification and large (4^o) field of view the finder allows to quickly locate the necessary objects and roughly control the telescope axis alignment.

Finder lens:
Lens diameter, mm	120
Focal length, mm	504
Focal ratio	1:4.2
Angular filed of view	4^o

The focal plane has grid with cross in it. The circle of 1^o09' angular diameter and the square with side of 1^o00' are marked around the center of cross. Sides of square are parallel to the lines of cross. Central cross has 1'.4 gap. Eyepiece provides compensation of vision in the range from -4.0 +/- 0.25 to +4.0 +/- 0.25 dioptres.

Finders are fixed to the bodies of visual and photoelectric guides. Their protective covers are opened manually. Connector of eyepiece grid illumination is attached to the small connector on the photoguide tube. The voltage used is 27 V.