Test results from resolution charts provide a narrow and often misleading snapshot of actual lens behavior.
The only reliable way to understand lens performance is by making real images in the field, and even then distance and subject matter can make significant differences. I recommend against making any lens choices based on test charts or MTF or other by-the-number silliness.
from "Understanding Field Curvature"
This of course is selective self-reinforcement on my part, since I've been saying essentially the same thing for years. Still, I believe we're both right. And although I've never been able to find the reference, I could swear that I once read that a Leica lens designer (that would have been during the Leitz years—it was probably Mandler) once said that the only way to get to know a lens is to use it for a year and that everything else is a shortcut. Entertainingly, Lloyd goes on to note that when you're testing a lens with field curvature, you can, using small changes of focus, prove that a lens is better than itself. Made me laugh.
Don't subscribe to Diglloyd? It's like having access to a lavish technical library. It's expensive, but Lloyd is probably the best equipment reviewer on the planet.
(I was going to add something about quality not coming cheap, but then I remembered what I charge for TOP and figured maybe that's a road I'd better not go down. Makin' myself laugh again.)
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