Note that more alignments have been ruined with sloppy collimation than have been fixed. Collimation of a good telescope should be approached with the same trepidation as changing the battery in your car. It's OK if you know how to do it but if you don't then it's best to have somebody show you how. The collimation screws in my telescope are fairly stiff and the instrument seldom requires adjustment but I have seen telescopes in which merely packing and unpacking the telescope from its carrying case is enough to throw the alignment off.

The object of collimation is to ensure that the three optical elements (corrector, primary and secondary) are all mutually centered on the optical axis and are parallel to each other. It is also important to ensure that these three elements are aligned properly with the baffle tube and mechanical axes of the telescope. For most commercially made Schmidt–Cassegrains, the primary mirror is not adjustable in tilt. Similarly, the corrector plate is firmly fixed to the front end of the tube and thus non-adjustable. The secondary mirror, however, is adjustable via three small screws mounted on the backside of the mirror support. In some telescopes the screws may have a plastic cap over them to keep out dust. If there is a fourth, central screw then do not touch that since it keeps the secondary from falling on the primary.