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| Re: Canon EF 24-70mm f/4L IS Resolution Tests! |
Roger -- I posted the following over on your blog site before I'd read all the responses following your post here. So I've slightly modified and added a point or two:
Roger — Great work!
Taking matters a step further, and possibly touching the “why” of your expectations that the rez fall-off wasn't even greater in the sides and corners: seldom do correction end with correcting distortion. As you mentioned, there is the straightening that crops into the original image. But also very common is the lens profile auto-correcting vignetting. I find this also very destructive of rez, and the programs do little to extrapolate and fill the gaps left by such correction, resulting gritty, moth-eaten corners (blue sky is the really obvious!).
On a worst case scenario, anyone who has ever de-fished a FF fisheye image knows how much space there is to fill in the vacuum left in the corners/edges. My point is I think you are very right in your expectation that the numbers in practical use are considerably lower than what you've come up with here. Sorry to give you any more work, but I’d be curious to see the figures if that area represented by vignetting were “neutralized”.
I’m getting pretty selective in my use of correction tools, and find myself often leaving distortion and lens profile unused so I can keep as much rez for straightening, cropping in, or using skew to correct perspective. I have a terrible habit of tilting the camera body to the side around 4 degrees, losing a lot of valuable real estate! Correcting that is my biggest need -- some of my cameras don't have viewfinder levels built in. So I'm even more sensitive to the lost from distortion correction and vignetting.
Least destructive to me seems to be removing CA, but even here, edge rez goes down. Still, going "grey" as opposed to magenta or green seems a plus to me.
What is a person to do?
Thanks so much for opening the can of worms and shining a Maglite into it.