If it's a singlet lens, the chromatic abberation (false color) will be horrendous. The images will be blurry and probably unusable. What's the focal length? If the focal ratio is reasonable, say f/6 or higher, about all you could do with it for astronomy is use it with a narrow bandpass filter, like an O-III filter or H-beta. Then you could use it on nebulae without a penalty from the chromatic abberation. You could also pair it with an energy-rejection filter and Hydrogen-alpha filter for solar use. Or grind it into a mirror, aluminize it, and make a reflector out of it. On Mon, Dec 8, 2008 at 10:17 PM, Dan Hanks <danhanks@gmail.com> wrote:

I have an old lens that I think came out of a theater spotlight. It's about 6" in diameter, flat on one side, convex on the other. I've tried holding it at arms length while holding an eyepiece to my eye and found that the combination can magnify things. I'm curious if it might make for an objective lens in a home-brew refractor, if I were to mount it up in some kind of tube or something?

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I'm not an optics expert by any stretch, but curious if it would be worth the effort to put together into some kind of frankenstein refractor. Thoughts?

Dan

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