Saturday, October 22, 2011

Bob's Knobs and the Unsharp Mask

In search of better pictures, but with a mind toward economy, I keep trying different things. On Schmidt-Cassegrain scopes, the major cause of poor performance is bad alignment of the secondary mirror. For my Celestron CPC1100, collimating (aligning) the secondary mirror is a pain. You have to risk scratching the front glass cover with a phillips screwdriver while you're looking in the eyepiece to make an adjustment. So clever Bob made up some replacement screws that don't need a screwdriver. These knobs make it easy to collimate your scope's secondary mirror every time you set it up.
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I replaced the phillips screws with Bob's Knobs. Easy.
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After putting in the Bob's Knobs, you need to do a rough collimation. Stand about 10 feet in front of your scope. See how the circular reflections are listing to the right? Adjust the knobs until things look symmetrical.
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 Then take the scope out and find a bright star. Defocus thusly and fiddle with the Bob's Knobs until the image is symmetrical. Just a small improvement in symmetry yields a huge improvement in clarity.
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Here's a moon shot I took this morning. In addition to the improvement from tightening up the collimation, I used the unsharp mask in Nikon's Capture NX2 to get further sharpness. Capture is a must-have if you have a Nikon DSLR.
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