Orion XT10, XT6, XT8 instruction manual Astronomical Observing, Star-Testing the Telescope

To start, turn the smaller thumbscrews counterclockwise a few turns each (Figure 22). Use a screwdriver in the slots, if necessary.

Now, try tightening or loosening one of the larger collima- tion thumbscrews with your fingers (Figure 23). Look into the focuser 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 watch- ing 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. If turning that one thumbscrew does not seem to be bringing you closer to collimation, try using one of the other collimation thumbscrews. It will take some trial and error using all three thumbscrews to adjust the telescope properly. Over time you will get the feel for which collimation screws to turn to move the image in a given direction.

Figure 22. The three small thumbscrews that lock the primary mirror in place must first be loosened before any adjustments can be made.

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 18e. Re-tighten the locking thumbscrews.

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 high in the sky and center it in the eyepiece’s field of view. Slowly defocus the image with the focusing knob. If the telescope is correctly collimated, the expanding disk should be a perfect circle (Figure 24). If the image is unsymmetrical, the scope is out of collimation. The dark shadow cast by the secondary mirror should appear in the very center of the out-of-focus circle, like the hole in a doughnut. If the “hole” appears off- center, the telescope is out of collimation.

If you try the star test and the bright star you have selected is not accurately centered in the eyepiece, then the optics will always appear out of collimation, even though they may be per- fectly 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.

Note About the Collimatable 2" Focuser (XT8, XT10 only)

The 2" focuser of the SkyQuest XT8 and XT10 can be col- limated using three pairs of push-pull screws located at the base of the focuser (Figure 13). The focuser was collimated at the factory however, and should never need to be adjusted. Focuser collimation is only required under very rare circum- stances but has been made available for this telescope should such a need arise.

5. Astronomical Observing

SkyQuest IntelliScope Dobsonians provide prodigious capa- bility for observing the many wonders of the heavens, from the major planets to deep-space nebulas and galaxies. In this section we give you some observing tips and briefly summa- rize what you can expect to see.

Out of collimation Collimated

Figure 24. 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.

Figure 23. The tilt of the primary mirror is adjusted by turning one or more of the three larger thumbscrews.

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