[APML] 80mm refractor as a guide scope? (was: ETX as Guide-scope)

["Frank Schwartz" <fschwartz@rcn.com>]

I've been kinda out of it for quite some time, but caught the tail end of
this discussion.  I have an 8" LX50 (2000mm focal length), and yes, I know
all the PEC problems, etc, so I don't need a lecture about that, but I do
know that OAG guiding is horrible and difficult.

I was considering using an 80mm short tube refractor I have for guiding.  I
have a 201xt, and yes, I know I should have an ST4, but again, this is what
I have- it works great through the OTA, but sucks through an OAG.  The
problem is, the 80mm refractor is a 400mm focal length, and I remember
reading something about that being a bad thing, and I don't remember why.
The refractor obviously has no mirror flop, even has a nice focus lock, and
if I use Chris Veddeler's mirror stabilizer gizmo, and mount the refractor
down tightly, there should be very little slop.  My question, I guess is, is
the 400mm focal length unusable?  What if I used a 2x or 3x barlow to make
it 800mm or 1200mm?

I have a 4.5" mak that I tried once, and although it seemed to work ok, it's
heavy, and anything much away from the zenith, even with proper weight makes
for difficult balancing.  This 80mm is light in comparrison to the mak, and
is a lot easier to mount on the OTA.

For the record, an LX-50 with the Jordan Blessing DEC fix kit, a concrete,
permanent pier (in my observatory), latitude adjuster, and a few other mods
guides just fine with a 201xt through the OTA with a camera mounted
piggy-back.  I have some rather nice shots thru my Nikon F2 w/ 300mm f/4.5
telephoto.  It just gets difficult with the limited magnitude the 201xt has,
the distortion through an OAG, and the fact that you're working with a
fraction of the usable view to find a guide star.

Suggestions?  Any specific articles in the archives about guidescope focal
lenghts?

Thanks
Frank Schwartz
(in between web sites)



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