Field Curvature of the Zeiss 15mm f/2.8 Distagon with Focus Bracketing
This extensive comparison incorporates MTF, a dual focus bracket and a visualization.
Even after using the Zeiss 15mm f/2.8 Distagon for over a year now, I found this scene and its analysis contribute to a much improved understanding of how to make the best use of the 15/2.8 Distagon: the field curvature and overall behavior is illustrated especially well, with the dual focus positions adding further insight. I now have a lot more confidence that I can use the 15/2.8 Distagon to its full potential.
Optimizing Focus for Field Curvature and Subject (Campfire / SUV)
While this discussion uses the Zeiss 15/2.8 Distagon, the approach taken can be applied to any lens, and hence it is recommended reading for all brands and lenses, particularly for wide angle lenses.