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Out of collimation
Figure 12.
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 right if the optics are
perfectly collimated. If the circle is unsymmetrical, as in the
illustration on left, the telescope needs collimation.
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
collimated, the expanding disk should be a perfect circle
(Figure 12). 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.
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 or finder-
scope. Never use regular glass cleaner or cleaning fluid
designed for eyeglasses
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.
14
Cleaning Mirrors
You should not have to clean the telescope's mirror very often;
normally once every year or so. Covering the telescope with
the dust cap when it is not in use will help prevent dust from
accumulating on the mirrors. Improper cleaning can scratch
mirror coatings, so the fewer times you have to clean the mir-
rors, the better. Small specks of dust or flecks of paint have
virtually no effect on the visual performance of the telescope
The large primary mirror and the elliptical secondary mirror of
Collimated
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, which is easily done.
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 3-
vaned 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 cap 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 loosen the three
screws from the end of the optical tube that are flush with the
end of the tube. Completely loosen all three of the flush
screws (do not loosen the other three screws) until the mirror
cell comes out of the telescope.
Now, remove the mirror from the mirror cell by removing the
three mirror clips that secure the mirror in its cell. Use a
Phillips head screwdriver to unthread the mirror clip anchor
screws. Next, hold the mirror by its edge, and remove it from
the mirror cell. Be careful not to touch the aluminized surface
of the mirror 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 deter-
gent, and if possible, a capful of rubbing alcohol. Submerge
the mirror (aluminized face up) in the water and let it soak for
several minutes (or hours if it is a very dirty mirror). Wipe the
mirror underwater 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 stream of lukewarm water. Any particles on the
surface can be swabbed gently with a series of clean cotton
balls, each used just one time. Dry the mirror in a stream of air
(a "blower bulb" works great), or remove any stray drops of
water with the corner of a paper towel. Water will run off a
clean surface. Dry the bottom and the edges with a towel (not
the mirror surface!). Cover the mirror surface with Kleenex,
and leave the entire assembly in a warm area until it is com-
pletely dry before reassembling the telescope.
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