Astronomical equipment, telescope, 3 3/6" refractor, metal / glass, maker unknown, used at Sydney Observatory, Sydney, Australia, 1874-1890
There are two main types of telescopes. One uses a curved reflecting mirror to capture an image of the celestial bodies the other uses a refracting lens to magnify the image. Refracting telescopes were the first type of telescopes to be invented, appearing in around 1608.
This telescope was likely used as a finder telescope on the Observatory's 11.4 inch refractor telescope (H9886). Finder telescopes are generally smaller instruments of low power and large field of view that attach to a larger more powerful telescope, such as H9886. They allow an observer to find a celestial object more readily, then swap to the larger telescope for more detail. The telescope was fitted with a camera and enlarging lens that magnified the Sun's image to four inches
In 1874, after two years of enquiries, the New South Wales Government Astronomer H. C. Russell acquired a number of new instruments in preparation for the upcoming Transit of Venus. One of these was a new 11.4 inch refractor telescope (H9886), purchased for the observation of double stars from the optician and instrument maker, Hugo Schroeder.
The 11.4 inch telescope was specially made to fit into Sydney Observatory's South Dome. The original dome built in 1858 was taken down and a larger dome built to fit the telescope. The telescope had a clear aperture of 11.4-inches and a focal length 12 feet 6 inches and Russell commented that while this shortened focal length was a disadvantage to definition it was an advantage to its light catching power.
The telescope was adapted for taking photographs of the Transit of Venus in December of 1874. For the Transit of Venus it was fitted with a camera and enlarging lens that magnified the suns image to four inches. The wet collodion photographic plates were placed at the end of the camera and held in place by a spring. The camera end passed into a dark room tent raised inside the dome and connected to the telescope by a flexible sleeve. A shutter was used to take the picture which was developed on the spot and another inserted immediately. Three persons working in this fashion managed to take one photo per minute. The telescope was also used by Russell on the 7th of May 1879 to measure the 'Gem' star clusters in Arago.
Geoff Barker, Assistant Curator, August, 2007
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