Portable telescope

The barrel of this non-achromatic telescope is made of hand-coloured vellum, decorated with gold-tooled motifs. Each of the seven draw tubes is also decorated with gold tooling. The eyepiece and objective lenses are mounted in lignum vitae and each has a sliding brass cover.

The style and workmanship, in particular the gold tooling on the barrel, suggest that it was made by Christopher Cock, a telescope maker working in Long Acre, London, in the late 17th century. He made telescopes, microscopes and other instruments for clients who included Robert Hooke, John Flamsteed and Isaac Newton.

Like many early telescopes, this example can be extended to a great length. This was to allow the use of lenses with long focal lengths in order to reduce the problem of chromatic aberration - the appearance of coloured fringes around the object viewed. Black rings on each draw tube indicate an optimum length in use of almost 1.7m.

Object Details

ID: NAV1543
Collection: Astronomical and navigational instruments
Type: Portable telescope
Display location: Not on display
Creator: Cock, Christopher
Date made: circa 1680
Credit: National Maritime Museum, Greenwich, London, Caird Collection
Measurements: Length: 574 mm (closed); 1666 mm (open to stop lines); Diameter: 80 mm (barrel)