Several of the test sites are pretty much aiding Canon/Nikon to make their lenses look better, by using older low res bodies for their Imatest routines. Any lens that works on an a7r
just works, believe me.
Much of Canon's inventory is simply not up to scratch exactly where lenses need to be 'good enough' - in the outer frame where low res sensors let them get away with lesser performance. a7s users are even reporting some Leica M lenses are not too bad on the low demand 12Mp sensor, so that is the effect.
Sony (not Zeiss) wisely opted to make the FE 24-70 excellent in its middle range, 35-55mm, where most images are produced. It will show micro-contrast no Canon zoom lens can deliver.
'Not similar at all: the canon is tested on a 22MP body, the Sony Zeiss on a 36. On a 36MP body it'll do very much better.'
"The whole story is revealed with the (EF 24-70/4) lens mounted on the full-frame 1Ds mkIII. With the aperture set to ƒ/4, we note areas of sharpness in the center of the frame, bounded by significant corner shading, at the 24mm, 35mm and 70mm settings. At 50mm and ƒ/4, we see the same spot of sharpness as on the subframe, but
it now covers a much smaller area, and there's
significant softness across the rest of the full-frame image area. It's worth noting that these results were found on the third of the three lenses we tested: on the first two lenses, results were poor indeed" Oh.
If you suggest that the Canon lens would benefit from being mounted on an a7r you are mistaken - what happens is that weaknesses become more apparent compared with strong performance - so while all image data gets a leg up from the extra 22% resolution, the image centres now look so much better than the outer frame that the overall impact is weakened severely - the image goes from 'wow' to 'oh' as your eye moves outwards to the corners.
This is the experience due to 36Mp not just the a7r - when this sensor was introduced in the D800 the exact same phenomenon was observed, even Nikon issued several statements about it, including a recommended lenses list among other tips on maximising IQ. See it on p16 in this document:
..and note the absolute paucity of prime lenses they recommend, this from a huge company with a huge inventory of lenses - there are
just three primes outside of the mainstay of DSLRs - telephoto usage. See also the emphasis on heavyweight pro zooms. Actually there is no Nikon 50mm lens considered 'suitable' in that list...how they must look at the FE55 with envy! Even their primes in the list, apart perhaps for the 85mm, are quite substandard from a 36Mp point of view.
Here is a terrific list of various lenses from various makers and how they go on the D800 - note how few non-tele/non-pro zoom Nikon lenses make the cut!
Note the Zeiss and Sigma lenses, among the Nikon pro zooms and teles.
If and when these crook old companies - Canon and Nikon - introduce 50Mp sensor cameras it will clearly be for the benefit of cashed up pros, not the enthusiast market Sony is providing for. As Zeiss says and I paraphrase: we don't think the big guys are making lenses good enough for the bodies they are producing.
So we have this strange situation where C/N are passing off as a great strength something that is in fact a great weakness for the great majority of their user base -
inadequate under-performing prime lenses in the focal length range most often needed - loads of them, dating from last century, not even up to 20Mp in most cases. Even the new ones like the $2000 (!) 24/1.4 are poor at wider apertures, so they have not learn much, it seems.
Sony (with partner Zeiss) is now the enthusiast camera and lens maker par excellence.
