If you can’t reach the focus to infinity (the stars) then the focuser of your telescope is too high. Maybe you should try to pull the primary mirror more in the tube with collimation screws in the back of you telescope. Perhaps this will sole the problem. But careful! If you screw to the wrong way (out) your mirror can fall out the cell!

Thanks for this ‘how-to’ tutorial.
I have a 6″ reflector telescope and a Sony A300 DSLR with T-ring and a 1 1/4″ adaptor. I can’t get a focus on anything beyond about 15m. Is the problem with the telescope or the camera? I’ve used the eyepiece adjustmant through the whole of its range, but with no success.