Colimating a Celestron EdgeHD SCT with Bob's Nobs
Posted 20 May 2019 - 04:49 AM
I changed my 8" EdgeHD's seccondary collimation screws with Bob's Knobs.
When I tried to collimate the scope (using an artificial star) I managed to centre the central hole while looking in the eyepiece. However I couldn't get to see any diffraction rings. It was only the central hole and a white hailow around it, hence I couldn't't collimate. I can't focus anything either. I am using an Electric Focuser.
What am I doing wrong?
Can I damage the scope/mirror if I over focus?
Your comments would be highly appreciated.
Posted 20 May 2019 - 06:55 AM
Not sure, but it sounds like you're too out of focus during collimation. That and the fact that you can't focus has me wondering if your focuser is working.
Posted 20 May 2019 - 06:59 AM
Is your electric focuser connected to the small stock focus knob or is it attached to the rear of the baffle? Make sure your two mirror locks are disengaged while you are trying to focus.
Posted 20 May 2019 - 09:13 AM
How far away is your artificial star? It is best to have it hundreds of yards away, both to better approximate focus at infinity and to make the pinhole appear small enough that your scope can’t resolve it. If you calculate the diameter of the pinhole in arc seconds at the distance from the artificial star you can compare the result with your scope’s resolving power, which is about 0.5 arc seconds. This requires a tiny pinhole at a long distance!