11
ary mirror. This is done by alternately loosening one of the
three alignment set screws while tightening the other two, as
depicted in Figure 12. The goal is to center the primary mirror
reflection in the secondary mirror, as in figure 10d. Don’t worry
that the reflection of the secondary mirror (the smallest circle,
with the collimation cap “dot” in the center) is off-center. You
will fix that in the next step.
Aligning the Primary Mirror
The final adjustment is made to the primary mirror. It will need
adjustment if, as in Figure 10d, 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 three spring-
loaded collimation thumbscrews on the back end of the optical
tube (bottom of the primary mirror cell); these are the wide
thumbscrews. The other three thin thumbscrews lock the
mirror’s position in place; these thin thumbscrews must be
loosened before any collimation adjustments can be made to
the primary mirror.
To start, turn the thin thumbscrews that lock the primary mirror
in place a few turns each. (Figure 13)
Now, try tightening or loosening one of the wide 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 fur-
ther away from being centered in the “ring” of the primary mirror
mark. When you
have that dot centered as much as is possible in the ring, your
primary mirror is collimated. The view through the collima-
tion cap should resemble Figure 10e. 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 and accu-
rately center it in the eyepiece’s field of view. Slowly de-focus the
image with the focusing knob. If the telescope is correctly col-
limated, the expanding disk should be a perfect circle (Figure 15).
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 donut. 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, 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.
Appendix B: Cleaning the
Optics
Cleaning Lenses
Any quality optical lens cleaning tissue and optical lens clean-
ing fluid specifically designed for multi-coated optics can be
used to clean the exposed lenses of your eyepieces. Never
use regular glass cleaner or cleaning fluid designed for eye-
glasses
Before cleaning with fluid and tissue, blow any loose particles
off the lens with a blower bulb or compressed air. Then apply
some cleaning fluid to a tissue, never directly on the optics.
Wipe the lens gently in a circular motion, then remove any
excess fluid with a fresh lens tissue. Oily fingerprints and
smudges may be removed using this method. Use caution;
rubbing too hard may scratch the lens. Never reuse tissues.
Cleaning Mirrors
You should not have to clean the telescope’s mirror very often;
normally once every year or so. Covering the telescope with
Figure 13.
The three thin
thumbscrews that
lock the primary
mirror in place
must first be
loosened before
any adjustments
can be made.
Figure 14.
The tilt of the
primary mirror
is adjusted by
turning one or
more of the three
wide collimation
thumbscrews.
Figure 15.
A star test will
determine if the
telescope's optics
are properly
collimated. An
unfocused view of a
bright star through
the eyepiece should appear as illustrated on the right if optics are
perfectly collimated. If the circle is unsymmetrical, as illustrated on
the left, the scope needs collimation.
Out of collimation Collimated
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