Collimating Nexstar refractor?

I've been looking for resources but haven't yet found
what I think I need. I suspect an expect is reading
saa ...

I have a Celestron Nexstar 102 GT refractor. It has begun
showing symptoms of a collimation problem - "comet tails"
on stars at high magnification. There are no adjustments
I can find on the objective cell, and no information in
any of the docs I can find from Celestron.

I've read this symptom on a refractor might also be caused
by a problem with the diagonal or drawtube. I've tried
a friend's diagonal, and also better brands of eyepieces,
with the same symptoms. I don't know how to check the
drawtube for misalignment.

How do I decide which adjustment this Nexstar needs and
apply it correctly? Does somebody have the procedure I
need written up somewhere?

I'll be very grateful for pointers. Thanks.

--
Glenn Holliday

Glenn Holliday wrote:

I have a Celestron Nexstar 102 GT refractor. It has begun
showing symptoms of a collimation problem - "comet tails"
on stars at high magnification. There are no adjustments
I can find on the objective cell, and no information in
any of the docs I can find from Celestron.

I've read this symptom on a refractor might also be caused
by a problem with the diagonal or drawtube. I've tried
a friend's diagonal, and also better brands of eyepieces,
with the same symptoms. I don't know how to check the
drawtube for misalignment.

How do I decide which adjustment this Nexstar needs and
apply it correctly? Does somebody have the procedure I
need written up somewhere?


Hi:

Do you mean at the center or near the center of the field OR out toward
the field edge (as 50% or so toward the field edge)? If the latter, you
just have to live with it (or buy expensive eyepieces, which can help
some). At f/5 the field is not flat. Expect stars toward the edge to
look...uh..."icky." ;-)

If the former, these (Synta) scopes can be collimated after a fashion.
All you can do is loosen the screws on the tailpiece/focuser where it
connects to the tube and move the entire rear assembly gently in the
required direction until good collimation is achieved. I've frequently
done this with Short Tube 80s with good results, though this is
certainly not an optimum solution.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
and
_The Urban Astronomer's Guide_
http://skywatch.brainiac.com/astroland/index.htm
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers:
http://groups.yahoo.com/group/sct-user

RMOLLISE wrote:
Glenn Holliday wrote:
How do I decide which adjustment this Nexstar needs and
apply it correctly? Does somebody have the procedure I
need written up somewhere?

Do you mean at the center or near the center of the field OR out toward

At the center.

All you can do is loosen the screws on the tailpiece/focuser where it
connects to the tube and move the entire rear assembly gently in the
required direction until good collimation is achieved. I've frequently
done this with Short Tube 80s with good results, though this is
certainly not an optimum solution.

Thanks Rod. I'll go to work on it.


--
Glenn Holliday