Charles,
Interesting comment about focal length and ED glass. I had it pretty much in my head that the lower magnification of the typical hand held binocular received less benefit from ED glass than the higher power of the more typical spotting scope. In other words, what I had always heard was that the ED glass benefit occurred with increase in magnification. I wonder if you could comment a little further there? I'm much more of a binocular guy and prefer a relatively higher power binocular on a tripod when I want to look long. Less strain on my eyes and I can see better with a 12x+ tripod mounted binocular than I can from 25x spotting scope.
As to the poll, I have and use all of the types, so there is no good answer for me. However I have come to really like the full size roof prism with open bridge, like the ZEN ED (and others) and have always liked mid sized porros like the Yosemite. I have a wish for a dream roof prism binocular in 7x35, with ED glass and about an 8.5* fov. I have a Swift Eaglet 7x36 which is really close to the ideal, but not quite.
Steve, Welcome to Hunting-WA!
There are two focal lengths (one for objective lens group, the other is for ocular lens group). To support 20x magnification power, a long objective focal length is required. It is much easier for light to converge with longer focal length optics (less aberration). However, when the light travel through ocular lens group with short focal length, the color abberation will get worse. The higher the magnification, the shorter the ocular focal length, the worse the color abberation gets. So your comment about higher magnification is absolutely accurate.
One reason you might feel eye strain from spotting scope is probably because it is not comfortable to view through one eyepiece vs two through binoculars. I have used some high quality 25x100 binoculars. They are as comfortable as the ZEN ED.
