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telescope tube slowly clockwise and counter-clockwise around the
polar axis, one brings tile star to the telescope viewfield centre. After
checking of tile circle setting, one tightens it with a nut.
In order to avoid resetting of tile polar axis and circles one should
choose the solid horizontal site. Best of all, it is a concrete section of
l.5xI.5 m size. The position of three supports of the telescope pier
should be marked on this site. The telescope is mounted according to
the marks on the concrete.
6.2. Photographic observations
The complete set of the telescope includes the bracket for a camera
with the help of which one can mount a miniature camera.
For this purpose the bracket is mounted on the axis of declimations
from the counterweight side and the camera is fixed to it with the help
of a captive screw.
The exposures witch are required for photographing the star fields
are tenths of minutes without hindrance of the street lighting. There-
fore, for this period of time one should see to it that the camera follows
the sky precisely in its diurnal rotation. With this purpose the Barlow
lens and the eyepiece with the reticle possessing great magnification
are inserted in the eye piece tube. Near the viewfield centre of the
camera one chooses the bright star to which the telescope is pointed.
To keep the star on the reticle cross-hairs is the problem for an observer
for the whole period of exposure. As the cross-hairs of the telescope is
not illuminated, the image of the guide star should be slightly defo-
cused in order to cross a light circle of the unsharp image of the star by
the cross-hairs and to keep the star in this position for the period of
exposure. For the whole period of exposure one rotates carefully a mi-
crometer screw of the polar axis.One corrects the position of the guide
star by means of the micrometer screw of the declination axis as well
in case of necessity. To obtain the minimum corrections in declination
the polar axis should be set as precisely as possible to the celestial
pole. One should remember that, if the polar axis is set incorrectly,
the images of the stars at the viewfield edges appear as dashes even in
the case when the star image is kept on the cross-hairs.
The bracket makes it possible to use the camera with tile remov-
able objectives, if their mass is not so great.
