Pentax 6x25 Porros (1 Viewer)

I've seen a number of Pentax 6x25 porros on ebay. They are a vintage chrome binocular with an 11 deg FOV. Has anyone had any experience with them? I assume the eye relief is quite short, but how is the optical quality? Was there more than one version?

Here's a picture of one.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260688173242&ssPageName=STRK:MEWAX:IT

Thanks,
Mark

Very interesting. I haven't seen this binocular, but looking at the pictures just now I can see that this type of naked prism design could make a wide field binocular like this possible because there's no wasted space inside a conventional body. Notice that the objectives and eyepieces are mounted directly to the prism shelf so that the back prism hypotenuse extends almost to the back of the eyepiece. I imagine the objective focal length could be as short as 75-85mm, so the eyepiece focal length might be 12.5-14mm which would only need a fieldstop of 15-16mm for a 66 degree field, so the prisms wouldn't need to be very large. Construction quality appears to be first rate. Looks potentially like an excellent theatre glass.

I've seen a number of bins made in this general style. Pentax, Bushnell (probably made by Pentax) and Nikon have all made them. The design seems to have been popular in the 50's and maybe 60's, but has fallen from favor more recently. Nikon sold a 7x15 commemorative edition not too long ago, but that's about it. I've always wondered what to call this design. Would "naked prism" be it? I wonder why it isn't popular anymore. It's rare to find a compact with a wide AFOV. These Pentax have a 4mm exit pupil and a 60 deg AFOV. A modern equivalent with enough eye relief for eye glass wearers would be a real gem.