2
For setting the declination circle fixed on the declination axis one should find
the declination of two-three bright stairs in the star catalogue or make use of
the declinations of the planets. With the help of the finderscope one brings the
star or the planet to the center of the field of view of the telescope at maximum
magnification. After that one sets the declination of the required star against the
index. The circle is to be fastened with a screw. Then one makes attempt to find
the second star by its declination. For this purpose one slackens the screws of
the axis brake and adjusts the telescope so that the declination of the star to be
sought is set on he declination circle. Fix the declination axis and, by rotating the
telescope tube slowly clockwise and counter-clockwise around the polar axis,
one brings the star to the center of the telescope field of view. After checking of
the circle setting one tightens it with a nut.
In order to avoid resetting of the polar axis and circles one should choose a
solid horizontal site. Best of all it is made of some concrete of .5x.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 site.
7.2. Photographic observations
Photographing star fields is carried out with the use of the telescope in the
main focus. To make it one should use a small size 35-mm camera or other
devices having fitting thread of 42x.0mm or 42x0.75mm. To mount a camera
it is necessary to remove eyepiece from tube and to mount a bushing with the
thread of 42x.0mm. If it is necessary one should mount an adapter on the bushing
when using the telescope with camera provided with the thread 42x0.75.
Mounted a camera one should make a focus it and to balance the
telescope.
The exposures, which are required for photographing the star fields, are tenths
of minutes without hindrance of the street lighting. Therefore, for this period of
time one should see to it that the camera follows the sky precisely in its diurnal
rotation. Near the center of the field of view of the camera one chooses the
bright star to which the telescope is pointed. To keep the star on the reticle cross
hairs of the finderscope is the problem for an observer for the whole period of
exposure. As the cross-hairs of the finderscope is not illuminated, the image of
the guide stair should be slightly defocused 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.
One applies minor corrections for a clockwork drive with the help of
handwheel 4 (fig. 9) keeping the star on the cross hairs for the whole period
of exposure. One corrects the position of the guide star with the micrometer
screw of the declination axis if necessary. 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, even in the
case when the star image is kept on the cross-hairs, the images of the stars at the
edges of the field of view appear as dashes.
