06-20-2016, 12:27 AM
Quote:BTW, these are the official MTFs for the lens:
(took a while to find them)
While such MTFs only show half of the truth, they are usually not totally off either.
In this case, it seems unlikely that there's a massive drop towards the edges especially considering the fact that this is a tele lens.
Actually, with telelenses there often is less of a drop-off than with wideangle lenses. What a lot of people do not seem to realize is that the laws which control non-mechanical vignetting, also control resolution to a DEGREE. Essentially the spread of light towards the edges caused by the AoV, not only cause vignetting by spreading the same light over a larger area, but also spreads resolution over that same area, with as result that one could go. e.g, from 100 lp/mm in the center, to say 50 lp/mm the corners just by that effect alone.
Because the AoV in telelenses is so low, especially in long ones, vignetting and the loss of resolution towards the edges is in principle less. This apart from the fact that telelenses are easier to correct for certain flaws than wideangle lenses. Vignetting in telelenses often is caused more by mechanical vignetting in the lens system rather than by optical vignetting.
What we currently see with high MP sensors like the latest FF cameras and with MFT cameras, is that we are seeing more or less actual resolution again of a lens over the entire width of the lens, rather than its limits caused by maximum sensor resolution and the artificial impact of analyzing systems (as compard to film).
Sorry, just thinking aloud here: maybe it could be worthwhile, or at least interesting, to calculate what the maximum edge resolution of a lens is based on AoV in relation to on-axis center resolution, and extrapolate from there how well a lens performs over the whole image. That would actually mean that it would be possible to establish a good quality scale for lenses and their measuring points at all the points used currently in lens tests, and hence make qualification of the results easier, like for the 5DsR .
Hmm. I'll see if i can find anything on this subject.
Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....