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
technic Veteran Member • Posts: 8,932
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:

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:

I agree that taking field curvature into account can be important for maximizing IQ across the frame, especially for infinity scenes with WA zooms. However, I remember at least one lens (Sigma 2.8/18-50 at WA) where I had to focus farther away to get better corners (for about f/2.8-f/5.6 aperture); which is difficult when the lens goes just a little bit past infinity

And there are more complicated cases, e.g. my 15-85IS has compromised corners wide open at the WA end with center focused near infinity, the corner softness looks like possible field curvature. But when I move the Liveview display as far out as possible (far corner is not possible, unfortunately) I don't see an improvement in the corners when going past infinity (at WA, center infinity is near 7m on the focus scale, with my copy). Maybe I should do more testing as it looks sharper in the corners for shots at e.g. 10 meters distance, but doing a solid test for this takes a lot of time ;-(

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