How to Align a Telescope Mirror

Put the laser collimator in the eyepiece hole of your telescope's sighting tube and turn on the laser collimator. If there is an eyepiece there, remove it first. You will know the laser collimator is working because a small red dot (the color depends on the model, but it is usually red) will appear on the primary mirror and on the secondary mirror. If you don't see any dots, check the collimator's battery.

Align the red dot on the primary mirror directly in the center of the mirror by using the primary mirror's tuning knobs to move the red dot around until it is in the center. Most telescope primary mirrors have a small cross hair or circle at the center of the primary mirror, which indicates where the red dot should go for collimation. If your mirror doesn't have one, try to get it as close as possible to what you think is the center. Consider removing the mirror sometime, measuring the center, and indicating it yourself with a sticker. This will make collimation much more precise than guessing with your naked eye.

Align the secondary mirror. Once the red dot is perfectly centered on the primary mirror, the next task is to align the secondary mirror. The red dot needs to appear in the center of this mirror as well. Many models of laser collimators are engineered in such a way that a you will be able to see the red dot through the collimator once the primary and secondary mirrors are aligned properly.

Remove the collimator and do a star test. To do a "star test" put an eyepiece in the sight tube and find a star, using the telescope. Once you are have one fixed in your eyepiece, completely un-focus the image by using the telescope's focusing knobs. As you un-focus the image, it will become so fuzzy that a lighter "ring" will appear around the original image. If the lighter "ring" is perfectly symmetrical around the darker sphere, then the telescope is collimated. If not, go back to the step one and readjust.