Nikon 50ED straight vs Opticron MM3
Based on reviews and eyepiece availability/selection I recommended the MM3 to a friend who purchased an angled body with the 24x eyepiece (special order via Eagle Optics since they don't regularly stock Opticron eyepieces or body only MM3). I had a chance to look through it a bit in the field this past weekend. I didn't do any rigorous testing, but the optical quality was excellent--a very comfortable view, good eye relief wearing glasses, bright and superb contrast, resolution across most of the field superb. Sun falling directly on the objective had minimal effect on the view, and performance against the sun and looking at ducks on the water with bright backlighting was excellent. The dual knob focus didn't seem necessary to me for what is inherently a low magnification scope, but it operated very smoothly and with no slop. The tripod mounting foot is definitely more robust (solid metal) than that of the 50ED, even the improved version that I have (with solid metal thread rather than helicoil) since Nikon replaced my original 50ED body under warranty.
In comparison to my straight Nikon 50ED with 27x WF eyepiece (same optical formula predecessor to the MC and DS versions but more compact and maybe not as efficient multicoating), the view was overall very similar. The most obvious differences to me were that the Opticron was not as sharp at the edges of the view (due to aberrations that I could not focus out) and that it had some blue color fringing and other CA around objects well off-axis (nearly nonexistent in the Nikon), but these differences were trivial (even to someone like me who likes to use the full view), and I don't think that I would select one scope over the other based on optics. Otherwise, the biggest differences were in size and weight. The MM3 is small, but the ED50 is definitely smaller in size and lighter weight. If you are the sort of person who would choose the Leica 8x20 Ultravid BL over the Nikon HG for its smaller size, you'll want to take the trouble to put together a Nikon 50ED kit. Otherwise, the MM3 is a great little scope with the option of fixed WA eyepieces, and here in the USA, getting the MM3 body only and with 24x eyepiece is easier than ordering the Nikon equivalent from Japan.
--AP