The Large dome of the Observatory houses the first telescope in Bulgaria mounted on a permanent foundation – The 6-inch (152mm) refractor has a focal length of 2200mm and an equatorial mount. It was manufactured by the company “Grubb” and installed in the Large dome of the Observatory in 1897. For many years it was used for practices – during regular training of Astronomy students. It also contributed to scientific observations conducted in the first half of the 20th century.