Abstract:

Tracking around the zenith requires a very rapid motion in azimuth, approaching infinity in the limit of a star passing exactly through the zenith.  The result is a  blind zone around the zenith for altitudeazimuth mounts. The zenith blind zone is mainly considered and some formulae are given for estimation of the dimensions of it. The effect of field rotation, which is another disadvantage for altitudeazimuth optoelectronic tracking system, is analyzed briefly. Two solutions to overcome the zenith blind zone are presented, which also leads to some directions for future investigation. 

Key words: altitude-azimuth mounts, optoelectronic system, blind zone