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 turn the R.A. slow motion control cable clockwise
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.
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
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 rear of the mirror cell 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.
14
mary mirror. Repeat this process on the other two sets of colli-
mation screws, if necessary. It will take a little trial and error to
get a feel for how to tilt the mirror in this way. When you have
the dot centered as much as possible in the ring, your primary
mirror is collimated. The view through the collimation cap should
resemble Figure 8e. Make sure all the collimation screws are
tight (but do not overtighten), to secure the mirror tilt.
A simple star test will tell you whether the optics are accurate-
ly collimated.
Star-Testing theTelescope
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
Out of collimation
Collimated
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 illustration on left, the
scope needs collimation.
Figure 11. Loosen one screw of one of the sets of
screws one full turn and tighten the adjacent
screw until tight to adjust the primary mirror.
