User's Manual

47
Maintenance
a. The only adjustments possible, or necessary, on
the Advanced Coma-Free Telescopes LX600 ACF
models are from the three screws (as shown in
Fig 15.)
Caution: Do not force the three collimation
screws past their normal travel and do not
loosen them more than two full turns in a
counterclockwise direction or the secondary
mirror may come loose from its support.
You will fi nd that the adjustments are very
sensitive, usually requiring only one-half turn
or less to produce the desired result.
b. While looking at the defocused star image, notice
which direction the darker shadow is offset in
the ring of light or notice which part of the ring is
the thinnest (Fig. 16,1). Place your index fi nger
in front of the telescope so that it touches one
of the collimation set screws. You will see the
shadow of your fi nger in the ring of light. Move
your fi nger around the edge of the black plastic
secondary mirror support until you see the
shadow of the fi nger crossing the thinnest part
of the ring of light. At this point, look at the front
of the telescope where your fi nger is aiming. It
will either be pointing directly at a set screw, or
it will be between two set screws aiming at the
set screw on the far side of the black secondary
mirror support. This is the set screw that you will
adjust.
c. Using the AutoStar II’s Arrow keys at the slowest
slew speed, move the defocused image to the
edge of the eyepiece fi eld of view (Fig. 16, 2), in
the same direction as the darker shadow is offset
in the ring of light.
d. Turn the set screw that you found with the
pointing exercise while looking in the eyepiece.
You will notice that the star image will move
across the fi eld. If while turning the defocused
star image fl ies out of the eyepiece fi eld, then
you are turning the screw the wrong way. Turn
the opposite direction and bring the image back
to the center of the fi eld.
e. If the screw you are turning becomes very loose,
tighten the other two screws by even amounts. If
the screw you are turning gets too tight, unthread
the other two by even amounts.
f. When you bring the image to center (Fig. 16,
3), carefully examine the evenness of the ring
of light (concentricity). If you fi nd that the dark
center is still off in the same direction, continue
to make the adjustment in the original turning
direction. If it is now off in the opposite direction,
you have turned too far and you need to turn in
the opposite direction. Always double check the
image in the center of the fi eld of the eyepiece.
g. You may fi nd after your initial adjustment that the
dark center is off in a new direction (e.g., instead
of being off side-to-side it is now off in an up-
and-down direction). In this case repeat steps b
through f to fi nd the new adjustment screw.
h. Now try a higher power eyepiece (e.g., 9mm
or less) and repeat the above tests. Any lack of
collimation at this point will require only very
slight adjustments of the three set screws. You
now have good collimation of the optics.
i. As a fi nal check of alignment, examine the star
image in focus with the higher power eyepiece
as suggested (h), under good viewing conditions.
The star point should appear as a small central
dot (commonly referred to as an “Airy disc”)
with a diffraction ring surrounding it. To give
a fi nal precision collimation, make extremely
slight adjustments of the three set screws,
if necessary, to center the Airy disc in the
diffraction ring. You now have the best alignment
of the optics possible with this telescope.
Inspecting the Optics
A Note about the “Flashlight Test”: If a fl ashlight or other
high-intensity light source is pointed down the main telescope
tube, the view (depending upon the observer’s line of sight and
the angle of the light) may reveal what appear to be scratches,
dark or bright spots, or just generally uneven coatings, giving
Fig. 16. Defocused star images. Misaligned (1, 2), aligned (3)
123