Rodensock APO-Sironar-S Focus Quality

Question

I purchased the 135mm f/5.6 Sironar-S for my 4x5 camera and am somewhat disappointed in the quality. The focus seems very different between the center of the groundglass and the edges. It is as though the lens doesn't focus in a flat field. I was photographing a church with no tilt just a front rise. The steeple and a cross on top were in the same plane in object space but on the groundglass the they did not focus at close to the same point. I had to stop down to f/32 to get everything in focus. I'm concerned because for certain pictures (lighting strikes), I want to shoot wide open at f/5.6, but I'm worried only the center of my image will be in focus. I bought this lens about 2 months ago. I'm using it on a Super Graphic. Any ideas on what might be wrong? Mike