I have looked on the Schneider website at the lens specs for these two lenses an d found that the Xenars have a lower value of distortion across a 4x5 frame. Doe s this make them better lenses than the Symmars? What is this field curvature I have been hearing about on Xenars? Distortion is very low on Xenars according to Schneider. Could we be misled by wrong data from the Schneider website? Anybody want to comment?