Wavy field curvature a la Nikkor 24-70 maybe? Well, probably not since you take that into account...
I remember considering this lens at one time but decided to scrape and save for a 24L (maybe even the first version) in the end as I don't fancy stopping down to f/2.8 or thereabouts to get acceptably sharp images since I have a f/2.8 lens that covers 28mm anyways.
I remember considering this lens at one time but decided to scrape and save for a 24L (maybe even the first version) in the end as I don't fancy stopping down to f/2.8 or thereabouts to get acceptably sharp images since I have a f/2.8 lens that covers 28mm anyways.