The focal length of a telescope is an important parameter in determining the
angular pixel size. This parameter is used for the purpose of determining the
relative coordinates (angular separation and positional angle) of double and
multiple stars, and the precise coordinates of extragalactic radio sources
(ERS) that are visible at optical wavelengths. At the Astronomical Station
Vidojevica we have collected observations of these objects using two CCD
cameras, Apogee Alta U42 and SBIG ST-10ME, attached to the 60 cm telescope.
Its nominal focal length is 600 cm as given by the manufacturer. To determine
the telescope focal length more precisely for both attached detectors, we
used angular-separation measurements from CCD images taken at Astronomical
Station Vidojevica. The obtained focal lengths are: F42 = (5989 ? 7) mm using
the CCD camera Apogee Alta U42 attached to the telescope, and F10 = (5972 ?
4) mm with the CCD camera SBIG ST-10ME attached to the telescope.
Near-field diffraction-based focal length determination technique
