Zeiss Double Astrograph

The principal instrument of the observatory, the Zeiss Double Astrograph, was located in a rotating wooden dome 8 meters in diameter constructed on the solid foundation offered by the northeast corner of the palace. It consists of a refractor with a 40 cm four-lens objective of 240 cm focal length, to be used as exclusively as a photographic camera, and a reflecting telescope with a 60 cm parabolic mirror of 200 cm Newtonian focal length and an equivalent 8.2 m focal length at Cassegrain focus. 

The four-lens astrograph took 30×30 cm photographs, particularly suitable for observations of variable stars and the determination of the positions of minor planets and comets. The reflector could be used with eyepieces, or with large astrophysical research instruments mounted at the Cassegrain focus that could be counterbalanced by large moveable weights.

Both instruments plus two finders and a guide telescope (itself an excellent refractor) are rigidly linked together and mounted on the same polar axis. Two large (61.2 cm diameter) flint prisms of refracting angle 4 and 8 degrees respectively could be attached singly or together at the upper end of the reflector or refractor, thereby allowing spectra to be taken over large fields.