I'm German and have had focus issues with my Canon 70D from the start. I'm one of the notorious testers and posters on one German forum and got a lot of heat for the whole discussion.
In short: The actual phenomenon only occurs under very particular circumstances. It can't be shown with test charts and/or under artificial light. I am able to show it with all of my lenses with apertures of f2.8 or wider.
- wide open lens, f1.0 - f2.8 (phenomenon instantly disappears from f3.2 onwards)
- phase AF via viewfinder only (or Quick AF mode in Live View)
- manual selection of the center AF field (instantly disappears when selecting any other field)
- small, distant objects that just fill the frame of the center AF field (at least 5-10m away, rather more).
The result are completely OOF images in the area where the focus should have been. The focus sometimes can be found very close to the camera instead of 100m away where the object was.
I am very much aware that these circumstances are all but practical. But still, the AF is completely off although it should be in high-precision mode with these lenses.
Lenses I was consistently (!) able to show the phenomenon with:
- Canon 50/1.8 II (50% of the images OOF)
- Canon 50/1.4
- Canon 40/2.8 (depends on viewing angle)
- Sigma 17-50 / 2.8 OS HSM
- Tamron 90 / 2.8 VC Macro
Other lenses that are mentioned very often are
- Canon 85/1.8
- Sigma 18-35 - Sigma 35
Arguments against all this have been brought forward:
- We Germans test too much. ;)
- Everybody with issues is too stupid to take images.
- flawed test setup. Nope - I tested on a sturdy tripod with mirror lockup and 10s timer, IS off and shutter speeds of 1/500 and faster!
- With higher f-stops, DoF only camouflages the issue. This argument is invalid since the DoF at these distances is huge and not much smaller with lower f-stops.
- The objects in question are impossible for any DSLR to focus. However, under the same circumstances, many other cameras have no problem whatsoever. I tested the same lenses in the very same situations with my T2i / 550D right after the 70D - no issues.
- The lenses are simply off, and we see classic back / front focusing. Wrong: 50% of the time, the 70D shoots perfectly sharp images in these situations. A classic BF/FF issue never hits the target correctly.
Just to be clear: I personally do NOT suffer from this phenomenon in everyday life. My 70D consistently shows it, BUT I never take images like this! Either I'm closer or I don't use wide open apertures on these kinds of objects - it just doesn't make any sense for me to shoot like that. I'm rather scientifically interested in the question where such a strange behavior might come from. Nobody has had the right idea in MONTHS. It is very irritating. Most hope for a firmware bug (some issue with the high-precision mode of the center AF field / double-cross sensor), but Canon don't react or reply that they can't find any issues. Sure, they only use test charts on short distances.
Anyway, I'm happy with my Canon 70D in everyday life, but there's a nagging feeling in the back of my head that always reminds me of the 1000 bucks I put in that piece of technology...
Christian - Bonsai MultiMedia
P.S. In addition, it's important to me to bring across that there is a multitude of reasons why an image is less than perfect. The issue we're talking about here is VERY specific, but the risk is very high to misinterpret ANY bad image as "the problem". I think that everyone who believes to have "the problem" should take a deep breath and check for all the other possibilities first: shaky hands, bad light(ing), wrong parameters or settings, lack of experience with the new camera (coming from the T2i, my first images were incredibly bad on the Canon 70D, simply because it was so much heavier and more complex), classic problems like old/bad/misaligned lenses or AF motors etc. Canon will only react or make a statement if we don't make fools of ourselves by sending them images or cameras where the issue was either behind the viewfinder or in the lens used.
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