[ATM] Odd collimation problem

[Jerry]

IF you are going inside and outside focus a significant distance....

The stars not shifting position indicates the optical axis is at least
parallel to the axis of the focuser. It might not be centered but it is
parallel.

IF the ccd were not square to the optical axis the focus would be different
at different parts of the ccd. IF the entire ccd field is in focus at the
same time it is squared on.

The symptoms describe a de-centered diagonal. With an f:4.5 it could be
designed into the diagonal holder. Did you build this scope?

You could use the same alignment procedure except make the in and out of
focus "appearant" centers of field land equal distance either side of the
center of the ccd field.

If you understand which way and how much the diagonal should be de-centered
and verify that it is proper, then I think your method should work well.

Or you could use a sight tube.


Jerry




----- Original Message ----- 
From: "Chris Dalla Piazza" <dalchri at hotmail.com>


The stars do not shift in position as I focus so I don't think this would be
misalignment of the focuser motion with the optical axis.



-----Original Message-----
From: James Lerch

Your secondary, focuser, or both, are out of collimation.  By collimating
using 
only the primary, you are able to get the optical axis of the primary to hit
the 
center of the ccd, it just isn't hitting the center of the ccd square (i.e.
the 
optical axis isn't perpendicular to the surface of the CCD).

If you use a simple site tube, you'll probably see most of the error right
away.