>I hope so! The Tamron at full aperture at 20mm had dreadful corner
>performance, and it wasn't even fixed by 5.6. I'm going to have to look at
>my series again. To my untrained eye, the whole field of houses looked
>identical over much of teh frame except for the very corners, but you say
>you see field curvature, so I'm assuming that means some sharpness loss as
>it gets towards the edges, but you say the edges come back again? I'm going
>to have to look more closely. What do you look at? Pick one detail and
>follow it from fstop to fstop? Look at edge acutance and how it varies
>across the field? I'm just wondering what you pick to evaluate, and what
>does it tell you?
>Nick

Field curvature can be like rubber laid over a doughnut, or any other rotationally symmetrical continuous shape, and can be used to even-up the
field flatness when it otherwise might have been unuseably curved (the 21mm Nikkor non-retro and the Rollei 3.5 Planar also do this [the planar FC is serious, and makes the camera almost unuseable at wide apertures]). I look for uniformity of detail or shift in focus (I make the possibly wrong assumption that they look the same near infinity) as I look from center to corner in the frame. David