Re: ATM recent letter exchange in AA13 between Clark and Suiter

[PFAFF2@delphi.com (Robert C. Pfaff)]

>
>There is an exchange between Tom Clark and Harold Suiterin the reader's
>forum.  Tom says that he sees scopes with large diagonals as having
>abnormally  bright sky background all over through the eyepiece's field
>of view, and Suiter says that this can't be so, that large diagonals
>ruin fine detail, not spread light everywhere.
>
>What is your experiences, thoughts and analysis?
>
>-- 
>Clear skies, Mel Bartels

I totally disagree with Tom Clark. I have used a 17.5 f4.5 scope 
for years with a small diagonal and I am now using my  folded 24 f4.5
with a 33% secondary. Both seem to have the same field darkness
at the same magnification . I had to use some strange baffles
to prevent skyfloding at the EP. When I first used this scope
with a open truss it had problems. The large secondary was
picking up light from the ground and floding the EP. A black
sock over the whole tube asm. solved the problem.

If the field is brighter with a large diagonal it must be
because the diagonal is not baffled enough and a large diagonal just
makes the condition worse. I see many cage asm,s that are just to small
to keep out stray light.

Do you loose a bit of contrast? Sure, but not sky brightening.
Suiter is correct, the math is true :-)


One ATM,s opinion
Bob Pfaff