The Schmidt Telescope

In 1949 a Schmidt telescope was ordered from the firm of Hargreaves & Thomson of London. Five years later work began on the construction of the Schmidt building, joined to the dome built in 1942 for the Carte du Ciel. The telescope was delivered in 1957; after several years for installation and testing, observational programs began in 1962.

The instrument has a spherical mirror 98 cm in diameter, with a 65 cm corrector plate (its aperture) mounted at the center of curvature of the primary near the tube opening. The focal length is 2.4 meters. The 20 x 20 cm photographic plate is placed at the focal plane, about half way down the tube. The usable field is about 5 x 5 square degrees, more than six times larger than that of the Carte du Ciel astrograph.

For spectroscopy it used a combination of three objective prisms at the tube opening; these prisms are among the most powerful in the world. The Schmidt telescope was used for about twenty years to study the evolution of star clusters by stellar spectroscopy and polarimetry; unfortunately, light pollution from the surrounding towns made the site unusable by the early 1980s.

Mounting: Fork mounting by Thomson & John Bowton Ltd

The severe deterioration of the instrument in recent years is clearly visible

Vatican Observatory 2025.09.27