Preparing the Telescope for Collimation
Once you get the hang of collimation, you will be able to do it quickly even in the dark. When trying it for the first time or two, though, it is best to collimate in daylight, preferably in a brightly lit room and with the telescope aimed at a white wall. It is recommended that the telescope tube be oriented hori- zontally. This will prevent any parts from the secondary mirror from falling down onto the primary mirror and causing damage, should something come loose when you are making adjust- ments. Place a sheet of white paper inside the optical tube directly opposite the focuser. This will provide a bright “back- ground” when viewing into the focuser. When properly set up for collimation, your telescope should resemble Figure 20.
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.
Using the included 2mm hex key, loosen the three small alignment set screws in the center hub of the
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 loosen- ing one of the three alignment hex screws while tightening the other two, as depicted in Figure 22. Do not make exces- sive turns of these hex screws or force them past their normal travel. A simple 1/2 turn of the screw can dramatically change the tilt of the mirror. The goal is to center the primary mir- ror 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 center) 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 mir- ror is centered in the secondary mirror, but the small reflection
Figure 20.
The SkyQuest XTi IntelliScope properly set up for collimation. Note the white paper placed across from the focuser, and the level angle of the optical tube. Ideally, the telescope should be pointing at a white wall.
Figure 21. To center the secondary mirror under the focuser, hold the mirror holder in place with one hand while adjusting the center bolt with a Phillips screwdriver. Do not touch the mirror’s surface!
Figure 22. Adjust the tilt of the secondary mirror by loosening or tightening the three alignment set screws with the 2mm hex key.
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