Originally posted by Fototim Simply because I don't photograph focus charts a lot.
I prefer to photograph the world as I see it, in three dimensions, not flat. When I watch a wall in real life, I see the objects in the corner as further away than a centered object. You loose that dimension when using a flat field lens. And that's why good lens designers usually makes lenses with field curvature, ON PURPOSE.
The exception is macro lenses, they usually are designed with flat field on purpose. Because they are intended for a different purpose, to reproduce the word differently.
I attached 1 shoots (not very good but that for showing the problem) and 2 crops. 1 center and one border crop. This shoot as the problem and it is not a wall // to the camera. In fact it is almost as plane as a wall but not parallel to focal plane.
Field curvature at this level is not on purpose. On FA77 I never have the problem even through it is a lens known to have been designed to be pleasing and not give highest possible resolution numbers. Many thing are under corrected on purpose. But FA77 is tele, with almost no distorsion and no field curvatuve. At f/8 everything is razor sharp borders to borders.
But as you can see on theses DA15 pictures really show the DA15 can be quite soft on border in bad cases. I don't need the crop personnaly, I notice it at normal viewing size. On the example it seems that if focus is put near infinite on center, border are not focussed on infinite and subjects futher away are really soft.
I think I need to investigate more, but if somebody can explain how to solve this issue (I have heard here to use hyperfocal distance ?) I'am glad to ear.