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The sample crops from TDP suggest that the performance at 50 mm (center of image) is worse than all other zoom lenses, including cheap ones, and that it does not improve substantially by stopping down, and that the copy variation is significant.
It is not about being less excellent than at the extremes, but about being the worst lens you can choose for 50 mm stopped down work. The sample #1 at TDP is that bad.
I find it strange that someone who has not used the lens, can dismiss several reports that support the results from TDP, based on measured numbers...Show more →
Not sure if you are referring to my post or to something else, but since I responded a bit negatively to the new "bad at 50mm" business I'll reply a bit.
The familiar "you haven't used the lens" criticism is useful as far as it goes, but at this point few of us have extensively used all three of the current 24mm-(more than 24mm) Canon L options. I have not used it yet, and I don't think I made any claims to have concrete personal experience with the 24-70mm f/4. I think I kept my comments in the realm of things that a person could reasonably observe both about the specific lens and about the general question of how lens performance is evaluated - at least that was my intent.
It is reasonable and possible to have something useful to say about a lens performance discussion from that perspective - though I'll freely acknowledge that long and intense use of a lens can inform one's opinion in other useful ways. (I have that experience with the 24-105, and I now also have some experience with the f/2.8 24-70 II.) My comments were more about how we judge lenses than about the specific performance of the f/4 24-70.
My points were basically two:
1. Forum discussions often seem to morph the observation that a good thing is best in condition A into an assumption that it must therefore be bad in condition B. I think that something like that may be happening here with the f/4 24-70 lens, where there doesn't seem to be much evidence that the lens performs in a manner that could objectively be described as "poor" at 50mm but just that this isn't its best FL. The real question isn't whether it is better or worse at 24mm, 50mm, or 70mm, but rather how it performs as a photographic tool for our purposes. We can say something similar about almost any zoom lens - I have yet to meet a high quality zoom that performs equally well at all focal lengths and apertures.
2. When comparing things like lenses, forum discussions (and similar comparisons) often can lead towards a false and simplistic assumption that one thing is "best" and that other things are "deficient" - e.g. we try to pick a winner and losers. My point is that there are so many factors in play - the photographer's specific needs, functionality, etc. - that this can be a false way to evaluate gear. In many, many cases we are actually comparing a number of things that are quite good. I believe that is almost certainly the case here, based on my actual experience with the 24-105 and the 24-70 f/2.8 II and on reading a lot of evaluations and commentary on a lot of lenses.
I went back to the original link that started this thread to see what the author actually said about the 50mm performance. Here is a quote:
"We did find that 50mm resolution was slightly lower than 70mm for every copy. The center / weighted average at 50mm for the 24-70 f/4 IS was 875 / 700, compared to 920 / 750 at 70mm. Not a huge drop, but it was consistent. This is a bit surprising, but not a total shock. Some wide angle zooms exhibit similar behavior and the dip in resolution isnít extreme."
(Emphasis added to original text.)
That is in line with the point I was trying to make. I hope this clarifies things a bit.
(edited after original post)