Alvan Clark and Sons

Although never widely known among the general public, in the worlds of astronomy and optics the name Alvan Clark has always called to mind the finest craftsmanship possible. With optical glass Alvan Clark was an artist with savant-like capabilities. It was said that with the tips of his fingers Clark could percieve imperfections in a lens that were invisible to the naked eye. In the last stage of the polishing process he used only polishing rouge and his thumb.

The nineteenth century, in some respects, was not that long ago. Telescopes in working order built during the nineteenth and early twentieth centuries are bought and sold nearly every week. They are common enough that the prices, generally speaking, are moderate-- considerably less than the price of a new car. A knowledgable and patient shopper can even turn up the occasional, flawless, turn-of-the-century refractor at roughly the cost of a modern computerized SCT. But if the name Clark happens to have been engraved on a working refractor (from either century), then the price goes up to at least ten thousand dollars per inch of aperture.

When looking at a Clark refractor it becomes immediately obvious that aesthetics has much to do with the valuation of these instruments, but to put one on permanent display is a waste of a good telescope. After a hundred and fifty years, most of these refractors still work and produce images to rival the output of the best achromatic doublets today. Over six hundred Clark & Sons telescopes have been acounted for. Many are still in use by individuals and by observatories, most notably the U.S.Naval Observatory's 26-inch scope, the 36 and 40-inch refractors used by the Lick and Yerkes Observatories. The Naval Observatory's telescope was delivered in 1873 and is still in frequent use, mainly to detect and observe double stars and planetary satellites.

The Lick Observatory 36" scope and the Yerkes 40" refractor were each, at their times of completion, the largest refracting telescopes in the world, a distinction the Clarks accomplished five times over the 87 year course of their company's life. The Lick telescope remains the world's third largest refractor. The Yerkes is still the largest, though it might be more accurate to call it the world's largest successful refractor.

In 1900, the Great Paris Exhibition Telescope was unveiled at that year's Paris Universal Exhibition. It had interchangeable lenses for visual and photographic uses, but its main primary lens diameter was 49.2 inches with a 187 foot focal length. The project was headed by François Deloncle (1856–1922) and took 8 years to build. It was made primarily for exhibition purposes and was so heavy, long and awkwardly mounted that pointing the scope was nearly impossible. Soon after the exhibition it was dismantled. All that remains are the lenses, which are still kept at the Paris observatory.

United States Naval Observatory: 26-inch Alvan Clark & Sons refracting telescope

 

 

 

 

 

 

 

 

 

 

Yerkes' 40" Clark Refractor, Paris Expo 49" and Alvan Clark 8-inch refractor respectively