Alexis Powell
Natural history enthusiast
There is a vagueness about field edge aberrations on this thread that I think is preventing a reader (at least this one) from understanding exactly how the HG performs off-axis.
Edge sharpness is primarily determined by two aberrations: field curvature and astigmatism. This old post attempts to explain how they interact.
http://www.birdforum.net/showpost.php?p=1879542&postcount=5
Geometrical distortions at the field edge are unrelated to edge sharpness. The first two posts in this old thread attempt to sort them out.
http://www.birdforum.net/showthread.php?t=161309
Some of Nikon's "flat field" binoculars (like the SE series) have employed an edge sharpness solution that corrected astigmatism well, but field curvature much less well (condition "c" in the first link), and a distortion solution that relied on a small amount of pincushion combined a small amount of angular magnification distortion (the Nikon EDG in the second link) . Are those approaches what the Monarch HG is using?
Henry
Thanks for this question--I was wondering the same. I'm guessing that the Monarch HG corrects astigmatism and doesn't correct field curvature much, but we don't have enough information to know whether anything at all is corrected. Can the Monarch HG view at the periphery be brought into sharp focus (even if not in synchrony with sharp focus in the center)? Is the periphery at its sharpest focus (even if still blurry) when the center is at its sharpest focus? I hope the former rather than the latter because I prefer a bin w/curved field and low astigmatism (e.g. Nikon 8x32 SE, Leica 8x32 BN) over a bin w/astigmatism but low field curvature (e.g. B&L 8x42 Elite waterproof, Zeiss 8x32 FL).
--AP