Prospect or opera glass, 18th century.
© Science Museum / Science & Society Picture Library
Known as an opera or prospect glass, this device is a small Galilean telescope. Fitted with a large front convex lens and a concave one for the eyepiece, this example has a tooled vellum main tube and a single leather drawtube. Unsigned, this prospect glass can be dated to the 18th century. Small telescopes of this type were popular for viewing the stage from afar when at the theatre or opera house.