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31
tube (bottom of the primary mirror cell); these are the wide
thumbscrews (Figure 31). 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 counterclockwise a few turns each.
Now, while looking into the focuser through the collimation
cap, turn one of the wide collimation thumbscrews a half turn
or so in either direction and see if the secondary mirror reflec-
tion moves closer to the center of the primary. That is, does the
“dot” of the collimation cap appear to move closer to the ring on
the center of the primary mirror? If it does, great, keep going
until you get it as close as you can. If it doesn’t, try turning
the collimation thumbscrew in the opposite direction. If turning
the one collimation thumbscrew does not seem to bring the
dot closer to the ring, try using one of the other collimation
thumbscrews. It will take some trial-and-error using all three
collimation thumbscrews 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 possible in the
ring, your primary mirror is collimated. Now lightly tighten the
three thin locking thumbscrews to secure the primary mirror
in place.
The view through the collimation cap should now resemble
Figure 27e. A simple star test will indicate how well the tele-
scope optics are 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 correct-
ly collimated, the expanding disk should be a perfect circle
(Figure 32). 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 tele-
scope 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. Point the
telescope at Polaris (the north star) if you do not have a mount
that tracks.
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. On larger lenses, clean
only a small area at a time, using a fresh lens tissue on each
area. Never reuse tissues.
Cleaning the Mirrors
In general, your telescope’s mirrors will only need to be cleaned
very infrequently, if ever. Covering the front opening of the tele-
scope with the dust cover when it is not in use will prevent dust
from accumulating on the mirrors. Keeping the dust cap on the
focuser’s 1.25" opening is also a good idea. Improper cleaning
can scratch the mirror coatings, so the fewer times you have
to clean the mirrors, the better. Small specks of dust or flecks
of paint have virtually no effect on the visual or imaging perfor-
mance of the telescope.
The large primary mirror and the elliptical secondary mirror of
your telescope are front-surface aluminized and over-coated
with hard silicon dioxide, which prevents the aluminum from
oxidizing. These coatings normally last through many years of
use before requiring re-coating.
To clean the secondary mirror, it must be removed from the
telescope. Do this by holding the secondary mirror holder sta-
tionary with your fingers (don’t touch the mirror itself) while
unthreading the Phillips head screw in the center hub of the
4-vane spider. Completely unthread the screw from the holder,
and the holder will come loose in your fingers. Be careful not to
lose the spring on the Phillips head screw.
Handle the mirror and its holder carefully. You do not need
to remove the secondary mirror from its holder for cleaning.
Follow the same procedure described below for cleaning the
primary mirror.
To clean the primary mirror, carefully remove the mirror cell
from the telescope. To do this, you must remove the four
screws that connect the mirror cell to the steel tube. These
screws are located on the outer edge of the mirror cell. Then
pull the cell away from the tube. You will notice the primary
mirror is held in the mirror cell with three clips, each held by
two mirror clip anchor screws. Using a Phillips screwdriver,
unthread the mirror clip anchor screws and remove the clips.
Next, hold the mirror by its edge, and remove it from the mirror
cell. Be careful not to touch the aluminized surface of the mir-
ror with your fingers. Set the mirror on a clean, soft towel. Fill
a clean sink, free of abrasive cleanser, with room-temperature
water, a few drops of liquid dishwashing detergent, and if pos-
sible, a cap-full of rubbing alcohol. Submerge the mirror (alu-
minized face up) in the water and let it soak for several minutes
(or hours if it is a very dirty mirror). Wipe the mirror under-
water with clean cotton balls, using extremely light pressure
and stroking in straight lines across the surface. Use one ball
for each wipe across the mirror. Then rinse the mirror under a
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