Pointing models for the Calar Alto 2.2 M and 3.5 M telescopes

The pointing properties of the 2.2 m and the 3.5 m telescopes of Calar Alto Observatory are discussed. An empirical approach for the pointing models was chosen. The procedure for the development of these models is described. Results show rms-accuracies between 2.6 arcsec and 4.0 arcsec for the Ritchey-Chretien and prime foci observations. The main parameters in the pointing models can be interpreted as encoder alignment errors, alignment errors of the mounting relative to the absolute reference system, and some flexure of the systems. The time dependency of the pointing model and tests of the tracking accuracy of the 3.5 m telescope are reported.