Scientific instruments are becoming increasingly collectable as our obsession grows with all things outer space. Not only are they beautiful and fascinating to look at, they are , on the whole, practical and usable.
Antique telescopes have all these attributes. The US enthusi- ast Bart Fried, founder and past president of the international Antique Telescope Society (ATS), says: "Collectors use them and have them as decoration. I used my telescope just last night to look at the Moon and Jupiter."
Mr Fried owns a 1909 4in-diameter Brashear telescope, which he bought four years ago for $6,000 (£3,300). It is now worth double that amount.
He says many ATS members are amateur astronomers or scientists. They also tend to be antiques aficionados with an interest in the history of astronomy. Some are telescope makers, others simply "telescope nuts".
"Interest in astronomy has exploded over the past few decades, at least at an armchair level," he adds, "and particularly in the US. As a result, the price of telescopes has really gone up."
The ATS has many British members but UK dealers say their customers are often more interested in telescopes for their decorative value than for their practical application. Saf Waterman of antiques dealer Trevor Philip & Sons in Jermyn Street, London, says that many of his clients buy telescopes as "toys for boys".
He has a 6ft-tall, 3in-diameter late 18th-century Dollond telescope for sale, with its own folding stand and wooden case, for £16,000. "Someone who buys this will have a large room with space to display it," he says. "They might use it but mostly it's to look at."
Dollond telescopes are particularly sought after. Their creator, John Dollond, patented an achromatic lens for the telescope in 1758; his sons John and Peter carried on the business. As optics and telescope making are intertwined, it is not surprising to learn that the firm is now known as optician Dollond & Aitchison. Other names to collect in antique telescopes are the German manufacturer Zeiss; Clark and Brashear in the US; and the British firms Troughton & Simms, Carey and Ramsden.
As with other antiques, the price of a telescope depends on several factors, including the item's condition, maker, rarity and age. Its decorative value is also important: Mr Waterman recently sold a hand-held telescope by John Haine in green and gold tooled leather, capable of expanding to five feet in length, for £35,000. Although it looks like the kind of telescope used by the captains of galleons to spy on enemy ships, it was probably made as an accoutre-ment for a gentleman of means and may never have left land.
Collecting antique telescopes is an expensive hobby but it is possible to pick up less pricey models that should still rise in value. The London company Broadhurst Clarkson & Fuller was formerly a telescope maker, but now only imports the instruments. It produced huge numbers of handheld, brass and leather telescopes up until the 1980s. "A good, clean example of one of these from the 1920s to the 1950s would be worth about £100 to £150 because they're really quite rare," says Broadhurst Clarkson & Fuller's Peter Gallon.
"Although thousands were produced, they were well used, so if you find one in good condition it could be worth buying." Examples turn up in antiques markets, collectors' fairs and, sometimes, in dealers' shops.
It is perfectly possible to buy a telescope purely for its decorative value. But unless buying from an accredited dealer, serious telescope collectors - like any antiques collectors - need in-depth knowledge in order to be sure that what they are acquiring is genuine. There are several books on the subject, and the ATS has many members who are happy to share their expertise. There are also several collections on public view, which you can use to increase your knowledge. For example, you could check out the telescopes on show at the Museum of the History of Science in Oxford, the Science Museum in London and the Whipple Museum in Cambridge.
When it comes to collecting, Mr Fried says "caveat emptor" is a wise motto. "The art and value of a telescope is in the lens," he explains, "and it's very difficult to tell if the lens is original - particularly if it was made from the 1920s onwards.
"EBay is a dangerous place to buy telescopes. There are a huge amount of junk telescopes there, coming from India. They make a terrible piece, put an English telescope maker's name on it and call it antique."
You should also beware of period fakes. When John Dollond introduced the achromatic objective lens in the mid-18th century, others forged "Dolond" and "Dolland" telescopes to try to cash in, so you need to know your Dollonds.
GET YOUR FACTS IN FOCUS
From £200 for a basic, fairly recent table-top telescope to upwards of £50,000 for a rare, old and well-preserved model.
The Antique Telescope Society, www1.tecs.com/oldscope; the Museum of the History of Science, www.mhs.ox.ac.uk; the Science Museum, www.sciencemuseum.org.uk; the Whipple Museum www.hps.cam.ac.uk; the Royal Astronomical Society, www.ras.org.uk