Thanks for the nudge. I am urged to buy the Biogon-C. It is on offer right now at several places.
Meanwhile, I have looked at the Canon 35mm images.
What is comonly known from MTF curves is that the wobble as the distance from the center increases, identifies some change in the focal plane. Many lenses go outward, sort of back-focus, towards the edges. Such as my Summicron 35mm Version one does. So one focusses on an object in the foreground, you open the dia to separate the work from the background, and then in the far corner all at once details show up . . . Many lenses have that, I have seen examples of older Noctiluxes doing that too.
In the Canon 35mm it is quite different.
There is field curvature. BUT THE CURVATURE IS TO THE FRONT.
So here a scene I took : specifically for its 'brick wall'.
And here a crop. Not how nice it is that the lady with her dotted shirt with yellow birds 'appear to be' in focus. Pleasant surprise. Isn't this what is most pleasuable in a picture? No 'vague ghosts' in the foreground? The lady is sharp, while the persons to the left are in a range of out of focus, there the wall is short of being sharp too.
- [Another lens I have, the M-Rokkor 28mm has this effect of front-focus to the edges too, when stopped down rather far to F8.]