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ES Comet Hunter/mak-newt collimation problems

Started by Gene Carsia, 09/21/2014 01:56PM
Posted 09/21/2014 01:56PM Opening Post
My ES David Levy Comet Hunter has never given decent views since purchased. After hours of collimation attempts w/ a 2" Hotech laser and a combo Cheshire/sight tube I threw in the towel and shipped it back to ES. Their customer service is great, but when I received it was still horrible- when tried on the moon it was never in focus. Maybe rough shipping, so I recollimated it and the laser is spot on, but a "focused" star looks like a small doughnut and moving the focuser one way looks like a horizontal line and the other side of focus is a vertical line-?astigmatism. Any ideas on what would cause this? Please help if you can.

Posted 09/22/2014 09:56AM #1
Astigmatism probably caused by tight mirror clips. The mirror should be loosely held, never pinched, and allowed to float on the mirror support. If the mirror is glued in place, then all bets are off and it's suitable for the trashcan.

Posted 09/22/2014 10:32PM | Edited 09/23/2014 04:53AM #2
Problem solved- removed the primary and was surprised to see the head of a large screw was protruding about 1 cm and actually made a divot in the mirror back due to the pressure applied when turning the collimation knobs. Once screwed in flush like the other two screws no more astigmatism. These screws can only be accessed by removing the mirror, so I can't see how I could have caused this problem. Anyone who owns this scope should be aware since I've never seen these screws on any other primary assembly. Anyway all's well that ends well. Rolando,thanks so much for your help.