Visuale Telescope

A “Visuale” Telescope is a large refractor designed to be used by an astronomer looking “visually” through an eyepiece (as opposed to telescopes designed to be used as photographic cameras). The Specola’s largest visuale, with a 40 cm objective lens of 6 m focal length and a set of 9 eyepieces and various accessories, was installed by Zeiss in 1935 on an equatorial mounting under a wooden dome 8.5 meters in diameter, located above the massive round tower housing the central spiral staircase of the Papal Palace.

The instrument was also provided with a Graff photometer for observing variable stars and with a micrometer for measuring double stars. Later on a Danjon stellar interferometer was added, to determine the distances and positions of double stars and the diameters of planets.