ATM binocular telescopes vs. binoviewers

[Peter Abrahams <telscope@europa.com>]

>what is the difference when viewing between a bino
>with two mirrors and a bino using a larger mirror and a bino viewer.

   I have used very well made binocular Newtonian telescopes (Swayze,
Szepanski, Sayre, & others); and Zeiss & Televue binoviewers.
   With the best quality binoviewers, the difference is that you can't get
the lower power, wide field views like with twin telescopes.   The long
light path through binoviewers means that if you use telescopes of f4 to f8
focal ratios, you need to barlow it before it enters the viewer; so if
you're comparing with twin telescopes of typical fast dob ratios -- f/4 or
f/6, the binoviewer is a higher power, narrow field instrument.  This is
assuming the bino-tel and the single scope used with viewer have the same
focal length for similar physical size & for identical magnification
(without the viewer); if you assume that the single, larger mirror has a
longer focal length - for focal ratio identical to the twin telescopes -
you 'lose' even more low magnification.
   That is the only difference that I have found - loss of low power.
   With binoviewers that are less than the best quality, there are more
differences; especially vignetting from small prisms, or light loss from
mediocre coating, even ghost images.
   All binoviewers used with fast scopes require corrective optics (barlows
designed with the correction in mind) because pasing the steep light cone
through thick glass changes the correction for SA.  If these aren't well
designed, you'll get superior images with twin telescopes.

>with a bino-scope we
>have 2 separate optical systems, with separate aberrations.  My thinking is
>that the brain integrates out the aberrations

If you've got bad zones in each of the mirrors, then yes there might be
some effect where the brain uses the sharper portions of the image.
Or -- If at the edge of the field, one scope is giving blurry images & the
other has sharp images -- yes, I suppose that you'd get a better view than
if you were just using the bad scope.  
But given a good or excellent pair of mirrors -- most aberrations of
concern are from the f/ratio of the mirrors & the type of eyepiece, which
would be identical on both sides.   
I can't figure out a fault with the idea you propose, but I don't think it
would be meaningful in practice.

>anyone think that it is possible for 2 optical systems separated by a few
>inches to actually see a difference in atmospheric turbulence?

You can see a planet 'snap into focus' on nights of unsteady seeing, so in
theory you might have situations where one scope is focused and the other
blurry.  But I think during those times, you might be wishing you were just
using one scope!

Either way, binocular viewing is very rewarding & addictive.
My personal solution is the binoviewer, since the setup & hassle factor of
binocular telescopes is significantly higher than monocular scopes.  But I
really enjoy viewing through the twin tubes that I've used.
--Peter
_______________________________________
Peter Abrahams   telscope@europa.com   The history of the telescope & 
   the binocular:   http://www.europa.com/~telscope/binotele.htm