Table of Contents
Advertisement
Precisely collimating a clear-aperture Newtonian telescope
can be a bit confusing and time consuming at first, but is nec-
essary to get the best possible optical performance. Once the
telescope is collimated, the mirrors should not need much
adjustment again unless roughly handled or jostled.
Figure 11.
If star test
images are not perfectly
round even though you
believe the telescope
to be well collimated,
try slightly tightening or
loosening the primary
mirror collimation
thumbscrew that is in
line with the telescope's
focuser.
care and Maintenance
If you give your telescope reasonable care, it will last a lifetime.
Store it in a clean, dry, dust-free place, safe from rapid chang-
es in temperature and humidity. Do not store the telescope
outdoors, although storage in a garage or shed is OK. Small
components like eyepieces and other accessories should be
kept in a protective box or storage case. Keep the dust cover
on the front of the telescope and the dust cap on the focuser
drawtube when not in use.
Your 3.6" CA reflector requires very little mechanical mainte-
nance. The optical tube is steel and has a smooth painted finish
that is fairly scratch-resistant. If a scratch does appear on the
tube, it will not harm the telescope. Smudges on the tube can be
wiped off with a soft cloth and a household cleaning fluid.
cleaning Mirrors
You should not have to clean the telescope's mirrors very often;
normally once every year or so. Covering the telescope with its
dust covers when it is not in use will prevent dust from accu-
mulating on the mirrors. Improper cleaning can scratch 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 performance of the telescope.
The primary mirror and the secondary mirror of the 3.6" CA
reflector are front-surface aluminized (enhanced 96% reflec-
tive for primary) and over-coated, 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
stationary while turning the center Phillips-head screw counter-
clockwise. Be careful, there is a spring between the secondary
mirror holder and the Philips-head screw; be sure that it will
not fall into the optical tube and hit the primary mirror. Handle
the mirror by its holder; do not touch the mirror surface. Then
follow the same procedure described below for cleaning the
primary mirror. You do not need to remove the secondary mir-
ror from its holder when cleaning.
To clean the primary mirror, carefully remove the mirror cell
from the telescope. Do this by removing the four screws on the
end of the tube that secure the primary mirror cell. Now, remove
the entire mirror cell from the tube. Completely unthread the
three large primary mirror collimation thumbscrews (actually
thumbnuts) from the primary mirror cell. The inner part of the
cell containing the primary mirror is now free from the cell's
rear end ring. The primary mirror will be cleaned attached to
the inner part of its cell, as it is permanently attached with sili-
cone adhesive.
Lift the mirror cell carefully, do not touch the surface of the mir-
ror with your fingers. Set the mirror (in its cell) on a clean, soft
towel. Fill a clean sink free of abrasive cleanser, with room-tem-
perature water, a few drops of liquid dishwashing detergent,
and if possible, a capful of 100% isopropyl alcohol. Submerge
the mirror and cell (aluminized face up) in the water and let
it soak for a few minutes (or hours if it's a very dirty mirror).
Wipe the mirror surface under water with clean cotton balls,
using extremely light pressure and stroking in straight lines
across the mirror. 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 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. Dry the exterior
of the mirror cell with the towel. Cover the mirror surface with
tissue, and leave it in a warm area until completely dry before
reassembling the telescope.
When reassembling the primary mirror cell, be sure the index
groove on the inner cell's face is oriented with the notches in
the end ring as shown in Figure 12. This assures the low point
of the primary mirror is properly oriented relative to the focuser
when the cell is reinstalled in the tube. Once reassembled, the
telescope's mirrors will need to be re-collimated.
If the primary mirror center mark washes off during cleaning, it
is easy to re-mark the mirror's center using a template. Trace the
outline of the primary mirror on a sheet of paper and cut out the
circle. Fold the circle precisely in half, then in half again. Cut the
very tip of the quarter circle and unfold the template. Center the
template on the primary mirror's surface, and mark the mirror's
center with the very tip of a felt tip marker (Figure 13).
7
Advertisement
Table of Contents
