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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

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The Zverev photographic vertical circle (PVC) of the Pulkovo observatory is in the process of modernization. The features of the vertical circle are: a)Maksutov mirror-lens optical system with small aberrations and wide passband: aperture: 20 cm, focal length: 200 cm, focal scale: 103 arcsec/mm.b)Very compact instrument: 140 cm total length, 60 cm — tube.c)Wide field: 25 × 25 mm = 40′ × 40′. Wide-field imaging can be combined with meridian observations.d)Easily-reversible instrument: reversing takes less than 30 seconds.e)Two divided vertical circles of glass. Photoelectric circle reading microscopes.f)Photographic micrometer in focal plane. This will be changed with a CCD micrometer.

The present-day realization of inertial coordinate system by means of traditional optical astrometry is the Fifth Fundamental Catalogue (FK5). The series of observations with new meridian instruments (CAMC, PMC-190, BAMC, HMC) show the significant correlated differences (up to 0.″1) of observational catalogues from the FK5. Moreover, FK5 mean epoch appears to be old (about 50 years ago) and FK5 proper motions would have essential errors owing to the fact that not many new original catalogues (only 25 in RA and 15 in DEC) were used when compiling FK5. It should be noted also that FK5 has a dissimilar accuracy of positions and proper motions of “old” and “new” stars.