On Sun, 29 Feb 2004 19:44:04 GMT, William Hamblen
wrote:

If your diagonal is not exactly collimated you can't collimate the
SCTcorrectly.

As long as you are collimating using a central star, you can tolerate quite a
lot of miscollimation in the diagonal when collimating your scope. The nature of
the limited adjustments on an SCT makes it quite obvious where the _scope_ is
best collimated, independently of the diagonal. This is not the case with a
Newtonian, however.


Changing the mirror spacing should not change the
collimation, only the amount of spherical aberration.

To be clear, I did not say that the collimation was dependent on mirror
position. But other aberrations are, and I think it makes good sense to
collimate the telescope with its optics in as close to optimal spacing as
possible.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com