[ATM] Two secondaries, one backwards

[artbianconi@blast.net]

I recently submitted an idea to friends at S*T*A*R  for a
critique that I hoped would solve a problem I have.

I would like to be able to move my head slightly and look
down through an second eyepiece instead of using a Telrad 
or
similar device.

With that in mind, I went to my engineering software and
inserted a second secondary (sic!) on the same axis as the
first one but aimed towards the sky instead. Then I simply
positioned a second eye piece next to the existing focuser
to view the sky through that opposed secondary. 

I reasoned that since the second mirror is in the shadow of
the first, there would be no additional obstruction of the
light going to the primary and I could develop the
appropriate lens combination for the second eye piece to
help aim the telescope. Perhaps a simple change in lenses
would alter the viewing field.

I concentrated on studying the mechanical feasibility of
such a design. The inappropriatness of my expectations and
my lack of optical knowledge were apparent and my friends
were quick to point out as much.

Since the attempt is an integral part of an exceptionally
light (purposefully!) 6" f-8 open truss "port-a-ball" type
telescope, it's important that the solution be of low mass.

What kind of lens(s) must I use to focus on the new 
secondary, view the sky with low magnification and not
obstruct the light path?

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