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Focusing

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Posted by Daniel Johnson on November 28, 2002 03:18:17 UTC

There are many ways to focus. One way that works is to rig some way to make an old eyepiece perfectly parfocal with your camera. By rummaging through a dozen old eyepieces, an couple of old diagonals, and by using the Parfocal Ring sold by scopetronix.com , I was able to find a combination whereby I could plop in an old diagonal-plus-eyepiece-plus-parfocalizing-ring and have it reach focus exactly at the same plane as my camera-plus-T-adapter combination. I made sure one day, by focusing on a distant glint of sunlight, that the camera was at perfect focus on the scope. Then I took the camera off and put in the old diagonal/old eyepiece, and slid the eyepiece carefully in and out of the diagonal until it reached perfect focus, and screwed the parfocal ring tight. I have a ton of old eyepieces and diagonals, plus old barlows, and I tried every combination. I could only make one come to focus, but it is perfect. I focus through the eyepiece on a star, and I know the camera will be fine when I put it on the scope in place of the eyepiece.
One nifty gadget sold by www.taurus-tech.com is a device specifically made for focusing their camera with your eyepiece, in much the fashion just described. I don't know if it will work for your camera, but it has some adjustability.
Another possibility is to make a mask for the front of your scope with two or three or four holes in it. (Try 3 three-inch holes for a 10-inch scope.) You point the scope at a bright star. If you are out of focus, you see three star images that merge into one as you reach focus.

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