Gordon,

Some tessars are like that. The 450 Nikkor M and the 14" Kodak Commercial Ektar that I have exhibit huge image circles, and are sharp almost to the very edges, quite unlike the usual tessars that are sharp in the center of the image circle and rapidly go to the worms the farther you stray from the straight and narrow. I have no idea why this is, but its kind of nice, isn't it?