> I've been kicking around the idea of making some 6" or so binoculars.
> After thinking about it for a while, the idea of making them out of a
> matched set of cassigrain optics seems to have taken hold. The obvious
> advantages are compact tube length and a binocular "feel" with the lenses
> out in front of the eyepieces. Gives them some style points, in my
> opinion.
>
There was a good description in S & T in the 70's of a 6"F15 Cassegrain binocular, on a massive equatorial mount. The whole instrument weighed about 600 lbs ! It looked like a collimation nightmare....
You really need a right angle bend at the back for comfortable viewing. This makes the optical path for a cass rather complicated. Why not build a dob binocular along the lines of the 6" F8's in S & T recently? I have built 8" f8's and they are very comfortable to use. It would be possible to view in the same direction as the sky if you used amici prisms in the place of the tertiary mirror.
Mark