When the EF 24-70 f/2.8L Mark II came out earlier this year it started lots of discussions, mainly because of the hefty price tag ($2299). With this price tag, basically same specs and no image stabilization this lens had to be very good. Indeed, this lens has an amazing image quality.
Roger Cicala at Lensrentals com compared the previous iteration of the EF 24-70 f/2.8L to the new one using Imatest to measure the resolution properties of both lens. Well, the EF 24-70mm f/2.8L II sharpness figures are excellent, better than it predecessor. But there was more Roger Cicala wanted to learn. There have been concerns by users that some copies of the EF 24-70mm didn't have the sharpness they were expecting. He compared 70 copies of the EF 24-70mm f/2.8L II to 125 copies of the EF 24-70mm f/2.8 to see if and how much variation there was in the resolution figures. There is, look at the next picture.
While the Mark II is clearly topping the Mark I, there are huge differences among both batches. Quoting Roger Cicala:
A look at the graph shows a couple of things. Overall, the range of variation of the Mk II lens is about the same as the Mk I version. (And these are recent Mk Is after we learned how to keep the 70mm variation to a minimum. It used to be much greater.)
You can also see that three of the tested Mk II lenses seem to be out-of-sorts. Even with 70 copies, though, it’s hard to be absolutely certain where the ‘acceptable’ cutoff should be by just looking at the graph. [...]
The bottom line is that 3 lenses out of the 70 copies were not up to expectations. That is a bit higher than the 2% unacceptable rate we usually see ‘out of the box’.
One other thing demonstrates the difficulty we have with one of the less-than-expected copies; they’re still better than the best of the 24-70 Mk I versions. They just aren’t as much better as they should be.
Ok, so the worst performing of the Mark II is better than the best performing of the Mark I lens, but variation is pronounced. There is more in Cicala's post, for instance the EF 70-200 f/2.8 IS II is compared to the EF 24-70mm f/2.8L II at 70mm. Check it out.