M3 2013-05-03 and triangle shaped stars

Decided a week ago it was time take out and clean the mirrors from my Newtonian. After cleaning and reassembly all the stars were triangular in my images. No collimation nor polar alignment helped. I was at it for several nights to no avail. I was almost giving up all hope when I stumbled on an article that mentioned that a very common error is tightening the primary mirror clamps to tight. This might result in warping the mirror. Taking out the mirror, loosening the clamp screws and only gently tightening them again did the trick. The M 3 image is taken after the exercise.