<title>Use of fiber optics in an astrometrical instrument</title>

Abstract

An idea for a photographic vertical Circle (PVC) was proposed by M.S.Zverev in 1960'. This instrument was used for the observation of the absolute declination of stars in Chile and Pulkovo2. Later in 1980-s modernization of the PVC was made. During its modernization fiber optics were used for improving the readings of the divided circle and making it photoelectrical instead of photographicaJ3. Therefore the precision of the observations were increased up to 0.05". PHOTOGRAPHIC VERTICAL CIRCLEA photographical vertical circle (PVC) was made in Pulkovo Observatory's optico-mechanical workshop from the idea of M.S .Zverev in 19601 • This instrument permits measurement of the absolute zenith distances of the celestial bodies up to 9 magnitude with accuracy up to 0.1". The instrument has the Maksutov objective (D=20 cm, F=200 cm) and photoelectric reading devices for glass graduated circles (now in process of upgrading with CCD device4).Two long series of observation were made with PVC, first in Chile (1964-67) and secondly in Pulkovo . The main purpose of these observations -the determination of absolute declinations of bright and faint stars in both hemispheres2. MODERNIZATION OF PVCSince 1977 the automatic system of reading of two glass circles was introduced into operation with precision of 0.05". Each limb is read by four photoelectric scanning microscopes. During the modernization of the PVC new ligth system of the microscope working fields were designed. The new peculiarity of this device was using only one light source with the fiber optics system for all four microscopes. Four fiber bundles and four transmitting optical systems were installed. The light thread is projected on the enter planes of all 4 fiber bundles and its images are projected on enter pupils of all the micro-objectives. Thus the Kehler illumination scheme was realized. This scheme makes sure the uniform illumination in the limits of several per cent in the working field of 2 mm.The selection of the mode of packing of pixel fibres is very important: in the case of illuminating fiber bundle, photoelectric signals are not so strong as in the case of imaging fiber bundles, when the signals are several times stronger. The selection of the optimal angle of inclination of fibre bundle to the transmitting optical system is essential.Prolonged exploitation of fiber-optical system of our instrument shows a high stability and reliability in the very complicated meteorological conditions of open dome (temperature up to -20° C, 100% of humidity, moisture, hoar-frost etc.). O-8194-1829-3/95/$6.OO SPIE Vol. 2476 / 75 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/17/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx