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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 42x1.0mm or 42x0.75mm. To mount a camera
it is necessary to remove eyepiece from tube and to mount a bushing with the
thread of 42x1.0mm. 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 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.
7.3. Telescope and atmospheric conditions
Telescope has a high magnification. In this case one should remember the
following feature. When increasing a magnification of telescope a distortion of
image to be made by aerial heterogeneity becomes more visible. It is a
scintillation and distortion of image of remoted objects, scintillation and distortion
of image of stars, reduction of sharpness of small parts of Moon and stars. So,
one should make a testing of telescope resolution by double pares of equal
brightness and permeability by photometric standards, observation of little
contrast parts of planets in good atmospherical conditions such as calm, high
transparence of atmosphere and low turbulent air torrents.
Because a resolution of telescope TAË-150K is sufficiently high the testing
should be made in atmospherical conditions which are valued by Pikerings
scale. It is 6 scopes that to allow obtaining the satisfactory and good images
when diffractional disk of star is visible constantly.