Just a general comment as to why we're seeing a lot more curvature in recently released lenses. It's a way for manufacturers to design a fairly fast lens with increased sharpness at a somewhat lower price point (and associated costs). In other words, unless the manufaturer intended to also correct for this curvature and pass along the costs with a very expensive lens, this now is becoming an acceptable alternative, There are many other factors to consider and it's somewhat of an oversimplification, but compared to flat field general use lenses, these lenses have excellent sharpness but exhibit a fair amount of curvature, some more than others.
Some recent lenses that illustrate this point are the Sigma 35mm f1.4, the Nikon 16-35mm f4 VR, the Voigtlander M mount 35mm f1.2and the Samyang 14mm f2.8. In the past, I think manufacturers were afraid to release such lenses for fear that there was no easy way to correct in the film only era....but with the advent of a relatively easy fix in software post processing, most users are more receptive to these compromises. You generally can't make a lens sharper than it is, in post processing, but you can generally correct curvature with use of software.
Dave (D&A)
