By Steve Walters, 1999
- Orient your scope so it’s easy to reach the collimation screws. South at
a slight elevation is a good position.
- At the center of the guide are the reference designations for the screws
and their orientation as you face the front of the telescope.
- Check the orientation of your collimation screws “A”, “B” and “C”. They
may be rotated from the guide depending on your mount and the direction you’re
pointing the tube. All that matters is that the screw that is lowest to the
ground be called “A” in the drawing and that the eyepiece be pointing up away
from “A”. The guide shows the eyepiece position with the dotted box (EP) which
is the eyepiece as you would see it from the front of the tube. Use a diagonal.
- To begin collimating, place a star at the center of the field of view of
a fairly high magnification eyepiece (I use a 12mm), focus the telescope and
then rack it out of focus with a counterclockwise twist. If you’ve never done
this before, use a fairly bright star but as you become more skilled, you’ll
find dimmer stars give better results.
- If the scope is properly collimated, you’ll see a perfect “donut” having
a black “hole” perfectly centered. If not collimated, the donut’s hole will
be off center to one side or another. Your first time, you’ll want to make
the donut pretty large, but with experience, a small donut (just slightly
out of focus) will be better.
- Simply note the direction of the hole offset and find the corresponding
image on the collimation guide. Each image has a label telling which screw
“A”, “B” or “C” to turn and the direction (clockwise CW or counterclockwise
CCW). Make VERY SMALL adjustments, 1/16 of a turn at a time.
- Remember to re-center the star to see the effect of the adjustment. Stars
at the edges of SCTs are distorted by other optical impairments such as field
curvature, astigmatism, etc. If you do not re-center the star, you are wasting
your time. Also, remember that it does not have to be the very same star at
each step in the iteration. Just center any star and check the shape of the
- Refer to your Meade or Celestron manual about the maximum number of turns
that these screws can be turned. Usually, it’s only 3 or 4 turns. Then, evil
will beset your secondary.
- Good luck and Happy Collimating! Your SCT will reward you with great images!