Quote Originally Posted by jeroldharter View Post
I don't think it is lens field curvature because I can measure
it on the easel with the levels. The lens is a Schneider
Apo-Componon 150 mm.
If the field is convex downward I'd expect easel center
to first come into focus then the corners with a mite
less extension of the bellows. Has that lens any
specific best magnification?

A long shot: By way of trouble shooting you might try
a red, green, and blue focusing. Dan