Zeiss Visual Telescope

The “Visual” telescope is a Zeiss 40 cm refractor; this design allowed for high magnification of small but bright astronomical objects. It was installed under a large wooden dome 8.5 meters in diameter resting on the massive round construction of the palace’s 15th century spiral staircase. Zeiss provided a 40 cm objective of 6 m focal length, together with a set of 9 eyepieces (providing a magnification on the order of 600 x) and various accessories. The observer looked at the object through an eyepiece attached to instruments such as a Graff photometer (made by Zeiss) or a Danjon stellar interferometer (constructed in the Specola workshop, to measure the distances and positions of double stars and the diameters of planets.