Please Help! I can't get my C-11 to focus!

 Hello Astromart.com, 

Please help me figure out what I'm not seeing here. I have a Celestron C-11 on a CGEM mount. I had a sharply perfect picture with the scope originally, until I installed a set of Bob's knobs to replace the collimation screws. After installing the knobs I collimated the scope to the best of my knowledge using the planets and a few stars, but nothing has brought that sharp picture back. I've cleaned the collector plate a couple times too. I am in Chicago and would really appreciate any help in person or via comments. 

Thank you Astromart.com

It could be atmospheric seeing that's ruining your images. In the last week or two the atmosphere has been very unstable in Northern Illinois, and you won't get very good images of the stars until the atmosphere settles down. It usually gets better toward the end of August as the weather cools down and the strong hot air flow from the gulf stops moving across our region.

Rolando