The Vacuum Solar Telescope has been described elsewhere by Dunn (1964, 1969). A brief summary of its characteristics is included here as background for discussing the computer control of this instrument.
This telescope is altazimuth in design. Image rotation is accomplished by rotating the inner tube structure together with all the auxiliary instruments. Azimuth and elevation torque motors drive the two mirrors at the top of the tower to track the sun automatically. The input to the servo is derived from a photoelectric guider. When clouds intervene, the servos are switched from the photoelectric guider to an electromechanical coordinate converter that also generates the signal for the rotation of the table. An elaborate 25: 1 synchro system connects the mirror servos to the coordinate converter.