The octagonal mahogany barrel, which is now damaged, is characteristic of telescopes produced in the 18th century for use on board ship. The barrel was designed for strength, since the techniques for manufacturing strong round barrels were not well developed at this time. The brass fittings include a single draw tube on which the maker’s name is inscribed as ‘Dollond, / London’. This was the firm started by the London optical instrument maker Peter Dollond (1731–1820). It was Peter's father, John Dollond (1706–61), who took out a patent for the achromatic lens in 1758. This type of lens eliminated the problem of coloured fringes caused by the distortion of light as it passed through the glass. The objective lens cap and parts of the eyepiece are now missing.