Roger Cicala: Understanding field curvature for fun and profit

When deciding which 35mm lens to buy, what do you want to know? How sharp it is? How it handles? How much it costs? I want to know what its field curvature looks like. (Spoiler: the plot on the right is from the little guy.) I’m not a fan of lens testing purely for the purpose of winning pissing contests. I am, however, a great fan of lens testing for learning how to best use a lens. There are a few tests I find particularly useful, and the single most important one is field...