Not everyone gets why an f16 test is necessary: ‘With a lens this wide, why stop down that far?’, they ask. Most of those people tend to be locked into the film paradigm: in truth, given that wide angle lenses uniquely struggle to deliver resolution to a 16MP full frame sensor, even sharpness across the frame can often only be achieved by stopping down to f11/16. Which is why I maintain that an f16 optimised lens is far more useful than an f4 optimised lens – certainly for architecture. It’s another reason why I find Zeiss optics typically more useful than Leica!
|Canon 14mm at f16 (centre)||Sigma 12-24mm at f16 (centre)||Nikon 14mm at f16 (centre)|
As you might have expected, resolution differences have flattened out somewhat by this point, but interestingly, it is now the slower Sigma that appears to hold the advantage over either of the more exotic primes.
|Canon 14mm at f16 (corner)||Sigma 12-24mm at f16 (corner)||Nikon 14mm at f16 (corner)|
I’ve dropped down the test sample a little to demonstrate what CA remains at f16. All the uPVC visible here is white: any trace of green and purple (Canon) or red (Nikon) is an aberrant optical artefact. The Sigma has none. Not only that, but by f8 the Sigma has practically no vignetting: its uncommonly even illumination retains contrast far better into the extreme corners, giving the illusion of greater accutance.