Prior to collimating the primary mirror holder, locate the three (3) screws on the end plate at the end of the tube. Unthread the three screws and remove the plate from the end of the tube. Under the end plate there are three (3) sets of two (2) screws. The shorter Allen screws push the mirror holder which is held by the longer outer screws. In order to make an adjustment, the outer screw is loosened while the shorter screw is turned in or out. Then, the outer screw is tightened. Only one of the three (3) sets is adjusted at a time. Normally motions on the order of 1/8 turn will make a difference, with only about 1/2 to 3/4 turn being the maximum required. Do NOT remove
or back out the holder screws more than one (1) to two (2) turns!
With Polaris or a bright star centered in the field of view, focus with your highest power eyepiece (i.e., one with the shortest focal length). This includes eyepieces in the 4mm to 6mm range. The star should be well centered to avoid confusing collimation problems with coma, a problem common to all Newtonian telescopes especially near the edge of the field. If you notice a flare in the star at one side (same side) just as you go inside and outside of exact focus, then collimation will help sharpen the image.
Take note of the direction of the flare. For example, if the flare is toward the 3 o’clock position in the field of view, then you must adjust the screw or combina- tion of collimation screws necessary to move the star TOWARD the direction of the flaring. In this case you want to move the star with the adjusting screw to the right, toward the 3 o’clock position in the eyepiece field of view. It may only be necessary to adjust the screw to move the star from the center to about half way or less toward the field’s edge (for higher power oculars). Prior to making any adjustment, it is advisable to gently back off the pressure on the three (3) outer screws to where they are snug, yet easily loosened without moving the telescope unnecessarily.
Collimation adjustments are best made while viewing the star’s position in the field of view while turning the adjustment screws. This way you can see exactly which way the movement occurs. It may be helpful for two people working together, while one views and instructs the other which screws are correctly turned and by how much. Start by loosening the outer screws and advancing an inner screw to see if the motion is correct. If not, undo what you did and try another set of screws.
IMPORTANT: After making the first of each adjustment, it is necessary to reaim the telescope tube to center the star again in the field of view. It can then be judged for symmetry by going just inside and outside of exact focus and noting the star’s pattern. Improve- ment should be seen if the proper adjustments are made. Since three (3) sets of screws are present, it may be necessary to move at least two (2) sets of screws to achieve the necessary mirror movement. Do NOT over tighten the outer holding screws!
Once in collimation, your telescope should not need additional collimation unless the telescope has been bumped or jarred severely. In fact, most observers will find the telescope’s collimation right out of the box to be satisfactory. Exact collimation is only necessary for discriminating observers that require optimal imagery. Adjust- ing the secondary mirror is NOT needed unless the telescope has been dropped or damaged. If it requires an adjustment, contact your local astronomy club for more detailed instructions, consult a telescope users handbook, or call the Celestron technical support department.
