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Do You Have A Scope?

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Posted by Daniel Johnson on April 20, 2003 03:26:29 UTC

If you use an ordinary 35mm camera with a 50mm focal length lens, you can use that lens on a fixed tripod for exposures of 15 or 20 seconds before the stars start to streak from Earth's rotation. For a typical ISO400 film, that will catch a lot of visible stars but not much nebulosity. If you have any way to piggyback your camera on a motorized, polar-mounted telescope (even a low-quality scope), you can extend that time to a few minutes without guiding, if your polar alignment is within a mile of being right. With your 50mm lens opened to, say, f/2 or so, a 3-minute exposure of the summer Milky Way near the tail of Scorpius will make your neighbors gasp and think you're a genius.
The choice of film can be hard. Lots of films don't show red hydrogen-alpha nebulae well (the Orion nebula, for example). I order Kodak Supra 400 film from adorama.com . It has nice color sensitivity at the important wavelengths for astrophotography.
Photographing through the scope itself is much harder, since the greater focal length magnifies Earth's rotation and reduces your time-without-streaking interval to a fraction of a second. Accurate polar alignment with a good mount becomes essential if you want to use the scope itself as a lens. If that's what you want, let us know.

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