Figure 20. To center the secondary mirror under the focuser, hold the secondary mirror holder in place with your fingers while adjusting the center screw with a Phillips screwdriver. Do not touch the mirror’s surface!
Figure 21. Adjust the tilt of the secondary mirror by loosening or tightening the three alignment screws with a 2mm hex key.
has a hole in the center and a silver bottom. This helps center your eye so that collimation is easy to perform. Figures 19b through 19e assume you have the collimation cap in place.
In addition to the collimation cap, the primary mirror is marked with a circle at its exact center. This “center mark” allows you to achieve a precise collimation of the primary mirror; you don’t have to guess where the center of the mirror is. You simply adjust the mirror position (described below) until the reflection of the hole in the collimation cap is centered in the ring. The center mark is also required for best results when using other collimating devices, such as Orion’s LaserMate Laser Collimator, obviating the need to remove the primary mirror and mark it yourself.
Note: The center ring sticker need not ever be removed from the primary mirror. Because it lies directly in the shadow of the secondary mirror, its presence in no way adversely affects the optical performance of the telescope or the image quality. That might seem counter- intuitive, but its true!
Aligning the Secondary Mirror
With the collimation cap in place, look through the hole in the cap at the secondary (diagonal) mirror. Ignore the reflections for the time being. The secondary mirror itself should be cen- tered in the focuser drawtube, in the direction parallel to the length of the telescope. If it isn’t, as in Figure 19b, it must be adjusted. This adjustment will rarely, if ever need to be done. It helps to adjust the secondary mirror in a brightly lit room with the telescope pointed towards a bright surface, such as white paper or wall. Also placing a piece of white paper in the telescope tube opposite the focuser (in other words, on the other side of the secondary mirror) will also be helpful in col- limating the secondary mirror. Using a 2mm hex key, loosen the three small alignment set screws in the center hub of the
tube, while turning the screw
Note: When making these adjustments, be careful not to stress the spider vanes or they may bend.
When the secondary mirror is centered in the focuser draw- tube, rotate the secondary mirror holder until the reflection of the primary mirror is as centered in the secondary mirror as possible. It may not be perfectly centered, but that is OK. Now tighten the three small alignment screws equally to secure the secondary mirror in that position.
If the entire primary mirror reflection is not visible in the sec- ondary mirror, as in Figure 19c; you will need to adjust the tilt of the secondary mirror. This is done by alternately loosening one of the three alignment set screws while tightening the other two, as depicted in Figure 21. The goal is to center the primary mirror reflection in the secondary mirror, as in Figure 19d. Don’t worry that the reflection of the secondary mirror (the smallest circle, with the collimation cap “dot” in the cen- ter) is
Adjusting the Primary Mirror
The final adjustment is made to the primary mirror. It will need adjustment if, as in Figure 19d, the secondary mirror is cen- tered under the focuser and the reflection of the primary mirror is centered in the secondary mirror, but the small reflection of the secondary mirror (with the “dot” of the collimation cap) is
The tilt of the primary mirror is adjusted with three spring- loaded collimation thumbscrews on the back end of the optical tube (bottom of the primary mirror cell); these are the larger thumbscrews. The other three smaller thumbscrews lock the mirror’s position in place; these thumbscrews must be loosened before any collimation adjustments can be made to the primary mirror.
To start, turn the smaller thumbscrews that lock the primary mirror in place a few turns each (Figure 22). Use a screw- driver in the slots, if necessary.
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