I seem to have a problem with my SCT and would appreciate any help
Basically, when I focus the telescope using the focusing knob, it reaches a point whereby the image starts to move. It moves out of the visual field. When I turn anymore in that direction, I hear this grinding sound, as though the mirror is pushed against something. When I looked inside the tube with a torchlight, there seems to be a screw that protrudes and prevents the mirror from travelling anymore.
Also, I am unable to reach focus with some eyepieces, esp the ones with very short focal lengths, like 5mm. But then again it is cloudy tonight, so maybe that's another reason.
The scope is a C11, and one possible issue might be that I've left it to stand on its main mirror (ie, where the scope cover goes) for a few months now.
Any suggestion/advice would be very much appreciated. Thank you very much for your time!