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Chif, where did you get your dob from? Is it a home-made one, or a manufactured scope? If it's home-made, the maker may not have done his math right, and placed the focuser a bit to close to the primary, or the primary is in the wrong type of cell. If it's manufactured, it may be too high up in the cell (collimation screws pushed in all the way, pushing the mirror forward). The main collimation cell, where the mirror is, actually "floats" in the mirror cell (the part attached to the tube walls). Collimation screws are typically about 3/4" long, so your mirror may actually be too far forward.
Of course, without actually seeing your scope, this is all just guesswork on my part. Can you post a pic of your scope?
Last edited by cmknight; 20-10-2012 at 02:06 AM.
Reason: Fat fingers
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