[Strider_ (Dylan)]

I have been collimating my 12 inch dob using a saxon laser collimator for about 12 months now. I watched a video on youtube showing my how to perform collimation. I had been turning my scope horizontal when doing this aligning the secondary then the primary. All was well... so I thought, my views to the best of my knowledge had been fine although I have nothing to compare it to? My issue is, when I last collimated my scope I turned it verticle with the collimator still in the focuser, the collimation was no longer centred on the target, the more verticle I moved the scope the more the dot moved. The collimator was secured tightly and could not move. The primary lock knobs were also secured tightly, as far as I can tell the secondary is tight also. Any ideas people? Rubbish collimator? Loose mirrors? Any help would be greatly appreciated.