I recently bought the Voigtlander 18 2.8 and find it very interesting and fun, but I'm having an "issue".
At f2.8, with focus set to infinity all is good, enough sharpness in the center slowly fading away towards the edges. As I focus back from infinity I immediately lose sharpness, so infinity mark is right.
Already at f4, but even more visible at f5.6 and f8 (and up) I got a strange behaviour (focus at infinity). The very center looks sharp enough, but then there is a big area around the center that loses sharpness (f8 is much less sharp than 2.8). Moving towards the edges (and closer to the camera in the low part) the sharpness gets much better! Focusing ever so slightly closer (my X-Pro3 says 10m on the display) the situation evens out a lot, increased sharpness in that area and a bit less sharpness on the edges. Again the area I'm talking about is phsically closer to the camera. An example here, f8 focus at infinity: www.matteobricchi.com/private/pictures/XT509312.jpg
Could it be field curvature? So strong? But it's like a wave, sharp in the center, then much less sharp and sharp again on the closer middle/edges.
This is so annoying to me, I cannot focus at infinity f8 and just shoot, I got that weakness which is really bad and pretty visible even without zooming. I always have to focus at infinity and step back that half millimeter to compensate...! Is it a "normal" behaviour of the lens or do I have a bad copy?
