How do I Set the Secondary Telescope Mirror With the Primary?

Adjust the collimation screws on the back of the primary mirror mount or cell so that the primary mirror reflects light directly back up the telescope tube. If you look down the tube from the open end with your eye at the center of the tube, you should see an image of the edges of the open end centered in the mirror. Adjust the screws and opposing springs till the mirror is aligned with the center axis of the tube.

Mount the spider mount and secondary mirror according to package instructions if the mount wasn't already mounted in the telescope. The instructions for this vary by type of mount and come with the mount. The mount is usually placed about 3 to 4 inches from the open end of the tube, depending upon the focal length of the primary mirror.

Center the spider mount body with the mirror so the mirror is dead center of the tube and reflects the image directly up the focuser tube hole. You will have to tighten and loosen the screws that mount the legs to the tube. Before tightening a leg to shift the position of the secondary, loosen legs on the opposite side of the tube, then tighten the leg that you want to tighten.

Tighten the collimation screws on the secondary mirror mount if yours come with adjustable screws. If the mirror is aligned, you should be able to look down the empty focuser and see your own eye reflected back to you in the center of the secondary mirror. Take it slow and easy so you get the mirrors perfectly aligned. If you collimate the mirrors well, your focus will be more crisp and focused and it will eliminate a distortion phenomenon called "coma" in which starts and objects in the scope have a false tail.

Check for loose collimation screws on the primary and secondary mirror mounts and finger tighten them until they are secure without putting pressure on the screw. Install the eyepieces when you're ready to look at the stars.