Opera or prospect glas with vellum tube, mid 18th century.
© Science Museum / Science & Society Picture Library
This miniature telescope is a instrument that has been variously called an opera or prospect glas. It is a small Galilean telescope that provides a low magnification using a large convex front lens with a concave eyepiece lens. This unsigned example is made of tooled vellum with a single drawtube and is dated to the mid 18th century. Small telescopes of this type were popular for viewing the stage from afar when at the theatre or opera house.