Meade Instruments Corporation - Meade LX200 Instruction Manuals
Fig. 27: Defocused Star Images
While looking at the de-focused star image and noticing which direction the darker shadow is offset in the ring of light or noticing which part of the ring is the thinnest (1, Fig. 27), place your index finger in front of the telescope so that it touches one of the collimation set screws. You will see the shadow of your finger in the ring of light. Move your finger (or an assistant's finger) around the edge of the black plastic secondary mirror support until you see the shadow of the finger crossing the thinnest part of the ring of light. At this point, look at the front of the telescope where your (or your assistant's) finger is aiming. It will either be pointing directly at a set screw, or it will be between two set screws aiming at the set screw on the far side of the black plastic secondary mirror support. This is the set screw that you will adjust.
Using the telescope's slow motion controls, move the de-focused image to the edge of the eyepiece field of view (2, Fig. 27), in the same direction as the darker shadow is offset in the ring of light. Turn the set screw that you found with the pointing exercise while looking in the eyepiece. You will notice that the star image will move across the field. If while turning the out-of-focus star image flies out of the eyepiece field, then you are turning the screw the wrong way. Turn the opposite direction and bring the image to the center of the field.
If while turning, you feel the screw get very loose, tighten the other two screws by even amounts. If while turning the set screw gets too tight, unthread the other two by even amounts.
When you bring the image to center (3, Fig. 27), carefully examine the evenness of the ring of light (concentricity). If you find that the dark center is still off in the same direction, continue to make the adjustment in the original turning direction. If it is now off in the opposite direction, you have turned too far and you need to turn in the opposite direction. Always double check the image in the center of the field of the eyepiece.
●You may find after your initial adjustment that the dark center is off in a new direction, e.g. instead of side to side off, it is off in an up and down direction. If this is the case follow steps 2 through 6 as described above to find the new adjustment screw.
●Now try a higher power (e.g. 9mm or less) eyepiece and repeat the above tests. Any lack of collimation at this point will require only very slight adjustments of the 3 set screws. You now have a good collimation.
As a final check on alignment, examine the star image in-focus with the higher power eyepiece as suggested above, under good seeing conditions (e.g. steady atmospheric conditions). The star point should appear as a small central dot (the so-called "Airy disc") with a diffraction ring surrounding it. To give a final precision collimation, make extremely slight adjustments of the 3 set screws, if necessary, to center the Airy disc in the diffraction ring. You now have the best alignment of the optics possible with this final step.
