I had the exact same thing with my first copy of this lens. I did return mine and got a better copy the 2nd time.
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Interesting, I didn't read far enough for that. I guess it sets the chips to different sensitivities, and then is basically line-skipping and doing the interpolation between them all. Ouch. I think I just hurt my brain trying to think of the math that's needed for some of this.
I have just received my (2nd copy) Canon 24-70 f/2.8 mk II. Being a faithful CR follower and reading http://www.canonrumors.com/tech-articles/how-to-test-a-lens/ I begain from the top and followed ever step I could as best as I could. I also have Reikan Focal and ran through every testing option there was available. What I have found suprised me to the point I originally thought I had received the dreaded bad copy.
There is a definite focus shift on the 24-70 mk II. I have found that from f4 to f5.6 it starts to back focus severely -5 afma vs +3 afma for f2.8 to f4 and +3 afma f5.8 on.
I am surprised there is not more information already out there on this.
I Found this on a competing forum http://www.fredmiranda.com/forum/topic/1177402 very similar findings
I understand through research you can hold the DOF button down to get around this issue? But would that reduce effectiveness of the f2.8 cross focus points?
After a quick search it appears the Tamron 24-70 has a very similar focus shift issue.
Does anyone have any advice? At this point I don't know what to do?
Thank you for your time.
Either exchange it again, or send the lens to Canon for adjustment. I'd say exchange it if you can. It might have a issue at 70mm.
Due to residual spherical aberration, a lens focus will appear to shift towards the rear, but the 24-70 should do it only very slightly. For the most part, its just the depth of field that increases more towards the rear as you stop down.
You can decrease the aperture on this photozone chart and see it.
Is this normal or is it just the new 24-70?
I've never noticed any shift from other than my 50 L and we all know that has some shift. I also never noticed any shift with any of my 70-200's and I use all lenses up close for 85% of my shots ..
I believe my copy of this lens does the same thing, but I am trying to redo my Reikan test (which produced + numbers -- opposite of expected result) and get time and conditions for a better test. Back focus observed in real-world exposures in which I would not expect last-second movement. But perhaps the same as your lens...
Did you find it only for close shooting distance or in general?
I found it happens to a considerable degree when shooting near MFD. I haven't looked into it much when shooting at greater distances. I suspect it is OK there.