Except for a remarkably strong curvature of field, the 24-70/f2.8L is rather crisp in infrared (on my Canon EOS 5D). The actual-pixels crop below was shot handheld in infrared (1/250 sec @ f2.8), and holds up with excellent detail. The only sharpening was “2” in Digital Photo Professional.
A larger crop [view] has been downsized (about 38% of the original).
Though curvature of field is pronounced on my particular 24-70/f2.8L in infrared, the lens is very, very crisp. I have yet to determine if the lens is “out of whack”, or if this is just an infrared phenomenon. Since I don’t currently have a color EOS digital body (just infrared), I can’t say for sure. But it came back from Canon with the statement that the lens had been adjusted to be “as sharp as it possibly can be”.
Sometime soon I hope to borrow an EOS color body so I can verify its behavior in visible light. I am not persuaded that Canon fixed the lens, as I see other evidence of problems which I don’t see with other lenses (sharper on one side than the other). This is not the first time I would have had to send a lens in twice to Canon (the 1st time it was a different 24-70/f2.8L!).