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.
Thank you for your time on this. After spending a few more days with the lens (and since BH is closed for Passover). I have had some more time for testing. I have (am attempting to) uploaded 2 files both taken at f4 about 78 inches away. The live view has achieved perfect focus and has equal ticks before and after the target. The AF photo is back focused and has its first tick in focus behind the target. Before I return for a second time, I want to confirm this is not normal and I should at least see at least one tick in front of the target in focus.
Looking at the photozone review of this lens there is a focus shift, but their copy has 2 ticks in front and 10 behind at f4, (vs mine has no ticks in front).
As a side note, I really do love this lens. The colors are amazing! Everything at f/2.8 is amazing.
As a secondary side note: when I don't use the center focus point and use one of the f/4 or f/5.6 points, the back focus is not as prevalent. I will try to upload some pics of that too.