Sharpness issue

Started 2 months ago | Discussions thread
anotherMike Veteran Member • Posts: 9,978
Re: Field Curvature primarily, lens performance at edges secondarily

One thing neither of us (or anyone else) has thought of, and it came to me later, in terms of a possible impact on things with the OPs image: The lens has some tilt, which isn't uncommon in a zoom.

So the lens has field curvature galore, and if we combine that with possible missed focus towards the front, and there is tilt that makes the field curvature in that part of the frame even worse than normal, he's in for a long day.

Diffraction is a limit on the maximum potential resolution at a given aperture. It's effect at the early onset of it does not substantially degrade the image to where low frequency (coarse structure) MTF information is destroyed, but rather, that there is now a limit to the high frequency structures that can be obtained. If he's shooting handheld, he's putting a limit on how much potential high frequency information he's going to be able to retrieve anyway, and no, his shutter speed is *not* high enough to guarantee he can match the resolution he could have achieved if he were on a tripod *and* precisely focused. So, once again, I honestly don't know why you're being so stubborn on this - diffraction is the last thing on the list of things degrading this image, and as such, given field curvature, possible tilt, possible mis-focus are the primary components of what is degrading this image, stopping down a bit more isn't going to hurt him in this situation. And to be honest - the subject matter itself doesn't contain a ton of high frequency detail.

Diffraction comes into play as something to be concerned with *when* you've got the other aspects covered. Missed focus, subject or camera blur (of even the slightest type), even atmosphere, are far more likely to conspire against an image that diffraction at F/8 on a D850. Hell, the diffraction limit at F/8 is about 78% contrast at 50 lp/mm, and that lens is nowhere near diffraction limited anyway at the edges at that aperture, so once again, yet more things that are negatively impacting the image before we can worry about diffraction. This would be an entirely different discussion if he were shooting a very high end prime lens on a serious tripod/ballhead in amazing light with perfect focus - then you'd be able to see some minor differences between F/5.6 and F/8. But this shot? Not going to happen.

And yes, I looked at where he put the focus point.

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