[APML] Autoguiding Focal Length

["Thom Iwancio" <tiwancio@sc.rr.com>]

Hey all, I think this has been discussed before so I apologize for
covering old ground.  I have been using a Lumicon OAG with my 8" SCT and
the built in focal reducer.  This places the autoguider at f10 and film
camera at roughly f6.  On of my partners says I should move the focal
reducer and guide at the reduced fl as well. His reasoning is two fold,
first it allows for more/brighter guide star choices and second it keeps
the CCD from chasing the seeing and every little bobble of the mount.
Guiding would essentially be at f6 and film at roughly f5. Is this the
way to go?

I know people have been discussing the feasibility of using extremely
short fl's like telephoto lens. It there a rule for guiding tolerances?
I have read Covington's treatise and he speaks of x number of mm's being
the resolution of the film and tolerances in mm's.  Unfortunately the
CCD world uses pixels converted to arc seconds. Or is this a trial and
error, see what works for me thing.

Thanks in advance,

Thom Iwancio
Elgin, SC
www.machunter.org


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