[APML]: collimation? was Mirror Flop

["John Petrush" <jpetrush@flosc.net>]

I suppose since I started the flap over mirror flop, I'll pause a moment and
summarize.  First, flop is inherent to the SCT design for a variety of
reasons, not the least of which are the pure economics of manufacturing
precision vs market price pressures.  Next, use of an off axis guider allows
the astrophotographer a way to work around this design comprimise with good
results; using a seperate piggy-back guidescope will likely produce poor
images.  But the design also requires careful attention to collimation.
Because of the large travel of the focuser (i.e primary mirror), the scope
should be recollimated when moving from one extreme to the other.

Am I on track so far?????

Now I get to admit my ignorance......  How does one collimate his/her scope?
I know it involves the set screws on the secondary, but what do you look for
and how do you know when you've got it right?  I'm pretty sure I've never
seen an airy disk through my C-11; I've always blamed it on the crummy
seeing of the high humidity, light polluted observing site known as my back
yard.  If I understand Tom Krajci correctly, the huge amount of refocus
required when switching between f/10 and f6.3 (using the focal reducer) most
likely throws off the collimation.  Is that a valid conclusion?  If so, it
seems I need to become skilled at recollimation.


I've spent a lot of time studying and taking photographs through my scope.
The results so far are encouraging, but clearly the work of a beginner.  The
experience just shows me that the more I know the more I know I don't know.
The insights and hard-won learnings of other's efforts will be greatly
appreciated.

John P