Corner tests for 16-35 f/4 vs. 16-35 f/2.8 (v.1) vs. 24-70 f/2.8L II

Started Jul 4, 2014 | Discussions thread
bronxbombers4 Veteran Member • Posts: 3,387
Re: Corner tests for 16-35 f/4 vs. 16-35 f/2.8 (v.1) vs. 24-70 f/2.8L II

Just another Canon shooter wrote:

Abu Mahendra wrote:

I understand it alright. The idea is very simple. If one wants to Know how a lens resolves in any given spot, one focuses the lens on that very spot. If one wants to Know how a lens resolves at point X, one does not focus at point Y. It ain't I who does not get this elemental concept.

What you cannot understand, even after I explained it in other threads, is what to do when you want to maximize the sharpness across the whole frame. It may sound very weird to you, but this is what the majority of the UWA users want. Get it? You want the corners, the center, everything in focus.

Field curvature can easily ruin the corners. The sharpness in the corners may depend heavily on how far you focus (in the center). PZ explains in here. In such cases, the solution is to focus close. Here is a picture that says it all:

source: PZ

If you have further questions, write to Klauss.

It's even trickier to manage to fairly best balance when comparing lenses than to user a real world scene and try to focus both at some point, with the latter, it's a bit easier so it's not a bad idea and then sure maybe corners are a mess on all shots, but if one lens makes them less of mess then it hints that it would probably deal better real real world when you are trying to balance things out (although field curvature can be complex, so not necessarily in all real real world cases would it apply if you focused on something that happened to make it not work out at an average basis).

It's hard to remember when looking at liveview exactly how you balanced things, it's hard enough to even 100% focus perfectly on one spot (which itself can take 6-12 trials) but then try to remember to what exact extent you balanced things and it's tricky. It can still be interesting to try it an see, but it's a bit dicier to then 100% pixel peep and make 100% definitive talk about corners, etc.

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