Peripheral AF point issue Tamron 24-70mm VC on Canon 5D Mark III

Started Sep 20, 2012 | Discussions thread
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Tim90 New Member • Posts: 6
Peripheral AF point issue Tamron 24-70mm VC on Canon 5D Mark III

Hi all,

I have just bought a Canon EOS 5D Mark III with a Tamron SP 24-70mm f2.8 VC lens. There seems to be a focusing issue with the peripheral AF points. When set at 24mm and shooting an object at 3m distance, the object is sharp when focusing with the centre point, but blurred when using the peripheral focus points (the problem being worse with the lateral peripheral points as they're further from the centre). With the camera on a tripod (VC disabled), I can focus using the centre point, then switch to a peripheral point, panning a touch, and without the camera/subject having moved, the lens will visibly refocus to a point 4 to 4.5m away rather than the 3m it correctly focuses on with the centre point. So when using the peripheral AF points, the object is blurred in the resulting image, but objects a metre or two behind it are far sharper. The peripheral points seem to be off and by a significant amount (focusing at 4 to 4.5m rather than the correct 3m). I've enabled only the cross type AF points and the problem persists (it’s a bit worse with the vertical AF points so I disabled them).

I can get around the issue by focusing manually using the peripheral AF points or by focusing using the centre point, half pressing the shutter, then recomposing.
The issue does not occur when using LiveView, only when using the viewfinder.

The issue seems most pronounced around the 3m distance and at the 24mm setting. I notice it less at 35mm and not at all at the 50mm & 70mm settings. Similarly, there's no issue when I use my Canon 100mm Macro f2.8 L IS USM lens or a friend's borrowed 50mm f1.8 II lens.

The issue occurs with no AF micro-adjustment and is not resolved by using AF micro-adjustment either.

Has anyone else with this body/lens combination encountered this problem? If you have suggestions to resolve it, then I'm open to ideas.

My real question (and problem) is whether it's a lens issue or a camera issue. It only occurs on a Tamron lens, which would suggest it's a lens issue. But since the problem doesn't occur in LiveView AF, only viewfinder AF, is it a camera issue? Unfortunately, I'm unable to test the issue using a different wide angle lens or identical body to be sure.

It's the key question, because I need to know which manufacturer to send the item back to for repair. Is this a known issue with a Canon 5D Mark III or with a Tamron 24-70mm f2.8 VC?

Canon insisted the body’s not at fault and that it’s a compatibility issue with a Tamron lens (and then tried to sell me a Canon lens). Possibly, but would focusing be off by such a huge amount? Wouldn’t the issue have been noticed in one of the many on-line reviews? Tamron said the lens may just need recalibrating, but again, the issue seems too significant to be resolved by a little recalibration.

Everything else about this lens is fine (image quality, VC, build quality), so if this is indeed just a bad sample, I’d have no hesitation in getting a replacement sample. If, however, this isn’t a bad sample and it’s related to Tamron-Canon compatibility issue, I’d advise against this lens/body combo as it’s a major issue often resulting in unusable images.
I'd appreciate any help or advice you can give me. Thanks!

Canon EOS 5D Mark III
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