Figure 13: The three small thumbscrews that lock the primary mirror in place must first be loosened before any adjustments can be made. A flat head screwdriver may be used to loosen these screws.
To start, turn the smaller thumbscrews that lock the primary mirror in place a few turns each (Figure 13). Use a screw- driver in the slots, if necessary.
Now, try tightening or loosening one of the larger collimation thumbscrews with your fingers (Figure 14). Look into the fo- cuser and see if the secondary mirror reflection has moved closer to the center of the primary. You can tell this easily with the collimation cap and mirror center mark by simply watching to see if the “dot” of the collimation cap is moving closer or further away from the “ring” on the center of the primary mirror mark. When you have the dot centered as much as is possible in the ring, your primary mirror is collimated. The view through the collimation cap should resemble Figure 10e.
A simple star test will tell you whether the optics are accu- rately collimated.
Star-Testing the Telescope
When it is dark, point the telescope at a bright star and accu- rately center it in the eyepiece’s field of view. Slowly
If you try the star test and the bright star you have selected is not accurately centered in the eyepiece, the optics will always appear out of collimation, even though they may be perfectly aligned. It is critical to keep the star centered, so over time you will need to make slight corrections to the telescope’s position in order to account for the sky’s apparent motion.
Figure 14: The tilt of the primary mirror is adjusted by turning one or more of the three larger thumbscrews.
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Figure 15. A star test will determine if a telescope’s optics are properly collimated. An unfocused view of a bright star through the eyepiece should appear as illustrated on the right if the optics are perfectly collimated. If the circle is unsymmetrical, as in the illustration on the left, the scope needs collimation.
6. Astronomical Observing
Site Selection
Pick a location away from streetlights and bright yard light- ing. Avoid viewing over rooftops and chimneys, as they often have warm air currents rising from them, which distort the image seen in the eyepiece. Similarly, you should not observe through an open (or closed!) window from indoors. Better yet, choose a site
Cooling Your Telescope
As a general rule, telescopes should be allowed to “cool down” (or warm up) before they are used. If you bring optics from a warm air to cold air (or vice versa) without giving it time to reach “thermal equilibrium”, your telescope will give you distorted views. Allow your telescope 30 minutes to reach the temperature of the outdoors before using.
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