Samuli Vahonen wrote:
Even it's "PLANAR" the field curvature is pretty bad, but at f/8 it's possible to shoot image which sharp from edge to edge. Good thing about field curvature is that the shape is round and smooth (e.g. no midzone dip). In practice when photographing 3D subjects, and not so much test targets, photographer can use the field curvature as to one's benefit. If you want to shoot planar subjects with wide aperture, please select some other tool for the job.
I've always loved the 50/1.4 ZE/ZF Planar. I still have a ZF.2 version that I use on the A7 series. I feel that the field curvature is quite a bit stronger on these cameras than when I used it on my ex Canon cameras. Probably because of the thicker sensor cover glass.
I actually think it has become nearly unusable for landscape shooting on my A7RII (I already felt this way ever since I starting using it on the first A7). It's sharp enough, but the curvature is so strong that I'm very often not able to get everything in the frame sharp. I'm not talking about planar subjects here but the usual 3D landscapes.
When focusing more to the foreground (like 1/3rd into the frame) you need to stop down a LOT to get the background edges in focus. When you focus more in the direction of the background... the whole center foreground is completely out of focus, while the foreground corners are razor sharp.
I go back to so many landscape photos from this lens on my old 5DII/6D and I never notice that extreme behavior. The same field curvature is there, just not nearly as strong. Such a shame, because it was one of my favorite lenses in my Canon days. It's the only reason why I now mostly use the FE55 for landscape shooting. Very minimal field curvature.