Optical quality of the Calar Alto 3.5 M telescope

The optical quality of the Calar Alto 3.5-m telescope with an improved Hartmann tester allowing for Hartmann tests as well as Foucault tests was examined. The radius containing 50 percent of the geometrical energy concentration was found to be 0.26 arcsec for the Ritchey-Chretien focus and 0.31 arcsec for the prime focus. Decentering coma is the main contribution to the optical aberration. The Seidel aberrations and the light concentration do not depend on the zenith distance. The actual focal lengths of the 3.5-m telescope differ by less than 0.08 percent from the specified values.