A telescope is an optical instrument that uses lenses or mirrors to make distant objects appear nearer and larger. Antique telescopes fall into two main types: refracting telescopes, which use lenses in a tube, and reflecting telescopes, which gather light with a curved mirror.
The refracting telescope appeared in the Netherlands in the first decade of the seventeenth century and was soon adapted by Galileo for astronomical observation. Isaac Newton built an early reflecting telescope in the 1660s, and in the eighteenth century the Scottish maker James Short became celebrated for fine reflectors. The London optician John Dollond patented the achromatic lens in 1758, greatly reducing the coloured fringes that troubled earlier refractors. Antique telescopes range from pocket spyglasses and naval telescopes with multiple brass draw tubes and leather- or wood-covered barrels to large library telescopes on mahogany or brass tripod stands. Collectors look for a maker's signature, usually engraved on the eyepiece draw tube, clear optics, original lens caps and, where relevant, a fitted case and accessories. Dents, missing parts and cracked lenses reduce value, while a fine brass library telescope remains a handsome addition to a study.
