Collimation is the process of aligning all components in a telescope to bring light to its best focus. All telescopes need to be collimated at some point. So what are we trying to do when we collimate our scopes? Just this: ensure that the eyepiece is aimed at the center of the primary mirror, and that the primary is aimed at the centre of the eyepiece. That’s it. End of story.

Option #1: No Tools

Star test images
This pair of star-test simulations shows an uncollmated scope (top) and one that’s properly aligned (bottom).
Yes, it is possible to collimate your reflector without any tools. It’s called the “star test.” The detailed ins and outs of this method are beyond the scope of this article, but essentially you centre a bright star in the eyepiece, throw it out of focus, and note where the shadow of the secondary mirror is positioned within the expanded disk of light. It should be centred. The test becomes progressively more sensitive the nearer you get to focus. Regardless of what other collimation method you use, the star test is the final arbiter of optical alignment. If it looks right in the star test, it is right.

Option #2: Collimation Cap

Collimation cap
A simple, inexpensive collimation cap.
Possibly your telescope came with one of these. Orion Telescopes supplies them with their reflectors, as do some other manufacturers. The device is simply a plastic cap with a small hole in its centre and a reflective underside. If your telescope didn’t come with one, you can make one with an old plastic film canister. For 90% of the collimation I do, this is the tool that I use. The only time I usually need something more is when I’m assembling a scope from scratch.

Best features: Cheap and effective.
Worst features: Not the best tool for aligning the secondary mirror (though it can be done). Requires the centre of the primary mirror to be marked.
Accuracy: Very accurate if your mirror’s centre dot is correctly positioned.
Ease of Use: Very easy to use.

Option #3: Cheshire Eyepiece

Cheshire eyepiece
This combination tool from Orion is a Cheshire eyepiece and sight tube in one.
Not an “eyepiece” in the usual sense of the word, a Cheshire is a sight tube with a small hole at the top that you look through, and a shiny surface tilted at 45° and aimed at a large hole in the side of the tube. The version Orion (and others) sell also has a set of cross-hairs at the bottom of the tube for aligning the secondary mirror. This “all-in-one” collimation tool is excellent. Indeed, if you have one of these, you need nothing else.
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