Orion SKYQUEST XT12 User Manual download pdf (Page 12)

Aligning the Primary Mirror

The final adjustment is made to the primary mirror. It will need

adjustment if, as in Figure 21d, 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

off-center.

The tilt of the primary mirror is adjusted with the three large

spring-loaded collimation knobs on the back end of the opti

cal tube (bottom of the primary mirror cell). The three smaller

thumbscrews lock the mirror’s position in place. These thumb

screws must be loosened before any collimation adjustments

can be made to the primary mirror.

To start, turn the smaller thumbscrews counterclockwise a

few turns each (Figure 25). Use a screwdriver in the slots, if

necessary.

Now, try tightening or loosening one of the larger collimation

knobs (Figure 26). Look into the focuser and see if the sec

ondary mirror reflection has moved closer to the center of the

primary mirror. You can easily determine this with the collima

tion 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. If

turning the one knob does not seem to bring the dot closer

to the ring, try using one of the other collimation knobs. It will

take some trial and error using all three knobs to properly

align the primary mirror. Over time you will get the feel for

which collimation screws to turn to move the image in a given

direction.

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 21e. 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 27). If the image is unsymmetrical, the telescope

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 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.

Note About the 2"s Focuser

The 2" focuser of the SkyQuest XT12 IntelliScope can be col

limated using three pairs of push-pull screws located at the

base of the focuser (Figure 20). The focuser was collimated

at the factory, however, and should not need to be adjusted.

Focuser collimating is only required under very rare circum

stances, but has been made available for this telescope

should such a need arise.

Figure 25. The three small thumbscrews that lock the primary

mirror in place must first be loosened before any adjustments can

be made.

Figure 26. The tilt of the primary mirror is adjusted by turning one

or more of the three collimation knobs.

Figure 27. 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 telescope needs collimation.

Out of collimation Collimated

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Comments to this Manuals

No comments

Orion SKYQUEST XT12 User Manual Page 12

Comments to this Manuals

Related products and manuals for Telescopes Orion SKYQUEST XT12