All binoviewers, regardless of brand, require a lot of IN travel, just because of their nature. You'll need at least the physical length of the binoviewer itself, plus any additional length from lateral and reverse reflections in the prism clusters. This puts them all in the 5 to 7 inch range, for the most part. *It's really more a question of matching a particular telescope to the bino-viewer concept, instead of finding a binoviewer for a particular telescope.* I have a 10" Newtonian that was built with about 6" of IN travel, to accommodate video imaging 19 years ago, but at f/5.6 there is considerable loss of effective aperture when using the binoviewer. The optical path throught them is very, very narrow, so sticking with f/10 and higher will mean you're using more of your objective- maximizing the light-gathering ability of the system. Think of it as trying to get a very wide-angle cone shoved through a narrow pipe. Won't work- only the central part of the cone goes all the way through. Only a very narrow angle cone will make it, unvignetted. I haven't discounted the idea of replacing the focuser on my 100mm refractor, with a lower-profile model, or even shortening the main tube. Many commercial refractors have enough travel as-is. And as I mentioned, SCT's are the ideal telescope for bino-viewer use by virtue of their focusing system and f/10 focal ratio. The good news is, all three of the scopes at SPOC are very well suited to bino-viewer use, by virtue of their designs. On Thu, May 7, 2009 at 6:38 AM, jim Gibson <jimgibson0@gmail.com> wrote:
Hey Chuch thanks for making me aware of that. I didn’t realize that there could be different kinds of issues with binoviewers.
I remember being at a star party and looking through someone’s binoviewers and how comfortable it was. I was thinking that a public star party would be a good place to have a pair for the comfort factor.
I may have to try out a few different pairs to see if I can find one that works on my equipment before I jump into this.