Re: [APML]: "Doughnuts" in AP Scope

[Michael Stecker <mstecker@earthlink.net>]

Mike Cook (and Chuck):
     I looked at your night time images at:
http://www.webcom.com/af9y/971217.jpg.  On the third row down and third
and fourth images from the left (#11 and #12) you show severe
vignetting. 
This is the type of vignetting I have seen with both the Lumicon Giant
Easy Guider at f/11 and the LONG rear adapter for my AP scope.  When I
received my 5-inch f/6 EDF AP scope, it came with two screw-in rear
adapters which would hold the standard 2-inch 35 mm adapter tube.  The
short adapter worked fine, but the longer adapter had a shiny interior
which resulted in the severe doughnuts.  Astrophysics has redesigned the
long adapter which no longer has this problem.  If you have one of the
older long adapters (before I bought mine) then you can use the short
adapter which works fine.  Also, in some of your images you show mild
vignetting of the corners.  I still get this vignetting myself with both
the 5-inch and 6-inch EDF AP refractors.  I was told by Brad Wallis that
this was caused by the relatively narrow T-ring for my Nikon camera.  I
wonder if this is also a problem with other non-Nikon cameras.  I also
wonder if the T-ring could be widened by a machinist which might solve
the problem.  Has any one tried this?

                     Michael Stecker