06-03-2019 08:27 AM
" I've now learned all about Canon MTF charts ..."
I don't think so.
MTF charts tell you a lot of technical data about a lab situation but very little about how the lens works in real photographic use. Maybe you don't have a great copy of that lens. Lenses are not all created equal. However using it correctly makes a great deal of difference in your results.
Keep in mind most UWA lenses will not be sharp edge to edge. If you are off center and not square to the subject this will be worse.
06-03-2019 08:43 AM
Great input from everyone. Just to follow up on my original post, I've now learned all about Canon MTF charts and the one for my 17-40 f/4L is truly awful!! See https://www.usa.canon.com/internet/portal/us/home/products/details/lenses/ef/ultra-wide-zoom/ef-17-4...
I'm attaching a better view of my original posted image, comparing left side to center to right side. You can see the problems are not a result of camera or people movement.
The good news is I did another similarly shaped group yesterday; this time used my 24-70 f/2.8L @ 34mm, f/9, 1/250, with terrific results - everyone sharp left to right.
I remember from long ago, before I ever even saw an "L" lens, that the 17-40 was not very highly regarded by serious photographers. Some even questioned why it qualified as an "L" lens at all. Both versions of the 16-35, the f/2.8 and the f/4, had a much better reputation.
06-03-2019 09:07 AM
06-03-2019 11:39 AM
I thought you mentioned the 2nd image was shot using the 70-200 f/2.8L USM (is that the version I, II, or III?). All of these are quite sharp. The version II improved on the corner sharpness just slightly over the version I ... but version I was no slouch -- they are all fantastic lenses (version III merely changed coatings on the lenses to reduce flare and the shade of 'white' pain on the lens barrel changed. It is mechanically and optically identical to version II other than those anti-reflective coatings.)
I did notice that if I right-click your images and tell the browser to open image in new window then I can see what appears to be the full size image. When I do this, I inspect focus around the edges from front to back looking to see if this is the result of very strong field curvature (the 'plane' of focus isn't really flat ... it's moderately curved). This does *not* appear to be field curvature (if it was ... I should have found something in the range that was in focus but I'm not seeing that.)
This makes me wonder about two other things. Please do some test shots with *just* the lens (no filters). Possibly the filters are to blame (what brand filters are these and do they appear to be completely clean?)
While ordinarily I might suspect the lens... you're showing the problem with two completely different lenses (and one of them has a reputation for being extremely good). This makes me wonder what your sensor looks like. The sensor in your camera is protected by a couple of layers of filters. I'm wondering if there isn't some sort of haze or residue on them.
Once upon a time, we used to smear a thin layer of vasoline around the edges of an otherwise clear filter to create a dreamy soft-focus effect around the edges of the image and ... this moderately reminds me of that.