Hello---I've been curious about how the image circles between these two lenses compare. Both, its said, will cover 12x20 with movements. Which lens has the largest, sharpest image circle?(forgetting for now that the Nikkor M's multicoated)I was under the impression that tessars generally have smaller useable(is that the word?) image circles than double anastigmats---certainly the 300 M is substantially tighter than a 12" Dagor, but why does the 450 M seem to "go on and on" if it is the same lens as the 300M in just a different focal length?---------Thanks!