6D AF behaviour

Started 3 months ago | Discussions
martin_k13
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6D AF behaviour
3 months ago

Hi,

Today I had to wait for some minutes, and I was chimping around with my 6D and the 24-70mm f2.8 lens. I own it for a few months now and I am quite satisfied so far. Technically I consider myself to be quite experienced, so I am well aware of what an horizontal and vertical AF sensor point is.

Please look at the following picture. It shows plain cupboard locks and handles. I was about 2m away, at 70mm.

There was absolutely no way my 6D could acquire focus with the scene above and all 11 focus points set to auto. Instead it was constantly focusing back and forth very fast in the macro-range(!) of the 24-70mm lens, the image in the viewfinder was completely blurry at all times. Funny thing is, when I switched to single AF field (center, as in the image above) the camera instantly acquired focus lock. I also checked other single af points, which seemed to work correctly, depending on their alignment (horiz/vert).

Any explanations/suggestions for this behaviour? I know that this is not a very scientific test, and I'm not a big fan of test charts and the like. But this confused me.

 martin_k13's gear list:martin_k13's gear list
Canon EOS 40D Canon EOS 6D Canon EF 50mm f/1.4 USM Canon EF 16-35mm f/2.8L II USM Canon EF 24-70mm f/2.8L USM +1 more
Canon EOS 6D
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Timbukto
Senior MemberPosts: 3,094Gear list
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Re: 6D AF behaviour
In reply to martin_k13, 3 months ago

martin_k13 wrote:

Hi,

Today I had to wait for some minutes, and I was chimping around with my 6D and the 24-70mm f2.8 lens. I own it for a few months now and I am quite satisfied so far. Technically I consider myself to be quite experienced, so I am well aware of what an horizontal and vertical AF sensor point is.

Please look at the following picture. It shows plain cupboard locks and handles. I was about 2m away, at 70mm.

There was absolutely no way my 6D could acquire focus with the scene above and all 11 focus points set to auto. Instead it was constantly focusing back and forth very fast in the macro-range(!) of the 24-70mm lens, the image in the viewfinder was completely blurry at all times. Funny thing is, when I switched to single AF field (center, as in the image above) the camera instantly acquired focus lock. I also checked other single af points, which seemed to work correctly, depending on their alignment (horiz/vert).

Any explanations/suggestions for this behaviour? I know that this is not a very scientific test, and I'm not a big fan of test charts and the like. But this confused me.

One possibility is that one of the outer points *knows* it is closer to you than the center point, but had difficulty locking in on the outer point due to lack of detail or closer than MFD. But if you are 2 meters away than there is no way you can be near MFD correct?

So possibly it is failing on the LEFT point which migth be considered close but lacks detail, or the TOP handle which may be difficult to focus on due to reflection.

Always love to learn more about 6D AF nuances. For example I learned that in order to get insane see in the dark AF, you need to be in AI-Focus or One-shot and not AI-Servo.

You can try process of elimination in this test if you can continue to replicate it.  Put black tape on the top handle or leftmost AF point and at the least you can see if it is either of those two that are confusing it (or any of the other points, but to my eye it looks like the left or top are the potential 'closest' distance).

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RandyB2
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Re: 6D AF behaviour
In reply to Timbukto, 3 months ago

I went to a seminar a couple of weeks ago where focusing was discussed. The seminar was put on by a couple of photographers that make their living shooting pictures for magazines like National Geographic. They highly recommended using single point focus and the back focus button. I've been using single focus for almost everything because you decide what to focus on and not the camera since they still can't read your mind. I had seen discussions on the back focus button but never used it. They convinced me I should. It will take some relearning since I've been using the shutter 1/2 push for decades. But what they said makes total sense.

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Randy

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AOKH
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Re: 6D AF behaviour
In reply to RandyB2, 3 months ago

RandyB2 wrote:

I went to a seminar a couple of weeks ago where focusing was discussed. The seminar was put on by a couple of photographers that make their living shooting pictures for magazines like National Geographic. They highly recommended using single point focus and the back focus button. I've been using single focus for almost everything because you decide what to focus on and not the camera since they still can't read your mind. I had seen discussions on the back focus button but never used it. They convinced me I should. It will take some relearning since I've been using the shutter 1/2 push for decades. But what they said makes total sense.

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Randy

Same ting here. I got used to it very quickly, though, and wouldn't want to have it any other way

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Regards. Anders

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martin_k13
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Re: 6D AF behaviour
In reply to martin_k13, 3 months ago

Just for future reference, if somebody else experiences my kind of problem: The weird behaviour got worse, and I decided to clean my lens contacts and use my rocket air blower to get rid of possible dust on the af/cmos sensor. Now the AF system is back to normal again!

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