Re: ATMing in the September Sky & Telescope

[MitchAlsup@aol.com]

 fundo@bellsouth.net write:

<< << Clyde's scope is in fact a Mersenne reflector, a design that doesn't
 get a lot of play amongst ATMs.  Given the number of interesting
 features this scope has, that is something of a surprise.  Perhaps after
 some of you have seen Clyde's piece in the September Sky & Telescope
 this will change.  >>
 
 Gary,  I have heard of the Mersenne design before, but I thought it was
 an afocal Cassegrain arrangement.  This should be interesting.  With the
 availability of ray tracing software, the imaging lens could be designed
 with the necessary corrections to make it work with current advanced
 eyepieces.  Is this what Clyde has done?  It seems to me that you could
 also cut your secondary obstruction to 10-15% of the primary diameter.
  >>
astrojoe@erols.com writes:

<<Back in 1994, Clyde attended Stellafane. He brought with him his trailer
and farm tractor to remove the 20" Mersiene from the trailer. We thought
it was novel at the time; but given today's larger DOBs, 40" and up, it
makes a lot of sense. I think we are going to see many more Mersienes
DOBs in the near future. Sure beats climbing the 8-10 foot ladder. The
design seems simple. The only question I have is how to optimize it for
a specific size mirror and refractor. Maybe Michael Pantratz could
comment on the design aspect optimization.>>

The Mersenne telescope uses two confocal paraboloids of the same
F/ratio. In this configuration, the secondary colimates the light cone
from the primary, and eliminates the inherent coma, astig, and field 
curvature. The colimated beam is the re-imaged by a refractor in
Clyde's incarnation. One can actually see through a Mersenne scope
without an eyepiece.

Since Only the F/ratio is fixed, the size of the secondary can be any
convienent size. Cylde choose his size based on his Genniss refractor
entrance aperture. When well focused there are two fields of view,
the magnified image off the secondary, and the field beyond the secondary 
that is within the FOV of the refractor.

Mitch