How critical is focus?
What about a 40mm lens at f/8 on a landscape scene— is focusing at 60 feet / 18 meters just as good as focusing at infinity and stopping down to f/8? Well, no, not by a long shot.
Excellent lenses are necessary for high resolution digital, but not sufficient.
The behavior shown in this comparison is not at all unique, nor confined to any brand or any focal length, though behavior varies. For example, see Field Curvature (Tioga Pass) in Guide to Zeiss for the 25mm f/2 Distagon.
Dr S writes:
Creates a lot of work for any photographer with a sizable kit....especially the landscapers! Having only read the above have you discovered the profound sharpness differences in other combos? The D800E w/primes or others? It would seem if one values detail and accuracy one needs to test every combo one owns.
Fascinating and eye-opening!
DIGLLOYD: the issues shown in this piece are present with most lenses, though it varies in degree and directionality. The understanding needs to happen once, but sub-optimal results from failure to understand the behavior of a lens goes on forever until understood.
Technical excellence has never been easy, something I learned with my 4X5. Also, in looking at the old 35mm slides taken in my youth, I clearly had not mastered many things at the time. High-res digital has its own severe demands.
Martin D writes:
“The uninformed photographer after shooting this scene will blame the lens, head over to an online discussion forum, and complain that the 40/2.8 STM is a 'dog'. ”
DIGLLOYD: Corrollary: “When I shot lens X on this scene, it was so much better than Lens Y. Lens X is a god, lens Y is a dog”.
Comparing lenses is a ton of work because doing it means repetition on different scenes for verification, and watching out for subtle errors and variations that will skew the results. Zoom lenses are trebly challenging, and comparing three or more lenses at once is much more work than two. A “quick test” generally means “not a test”.