7D + 70-200 F4 IS - Lens Won't Focus

Hello!

I was playing around with my 70-200 F4 IS on my 7D and I noticed that the camera would not engage the AF of the lens in two particular scenarios:

1) Lens focus set to infinity. Attempt to focus on object ~4-5 ft away. AF confirmation light blinks in VF. No AF attempted by camera/lens.

2) Lens focused to minimum focus. Attempt to focus on object ~ 15 ft away. AF confirmation light blinks in VF. No AF attempted by camera/lens.

Is this normal behavior? Is it due to the lens+camera combo? Or a camera issue only?

I haven't encountered this behavior before (or at least wasn't paying attention if it did happen before). My experience/thoughts have been that Canon cameras will cycle through the focus range at least once in an attempt to find something to focus on. I've never encountered the AF detector just giving up from the start.

If I set the focus closer to the actual object distance, the AF will kick in, as it should. But what if I'm in a scenario where I need to go from MFD to 15+ ft? Based on this event, I would have to guess the camera/lens combo will fail in that scenario. My expectation would be that the camera would at least make one attempt though the focus range to find something. Is my expectation too high?

Perhaps this is a repair issue?

This doesn't sound right. You should never have to set your focus manually in order for AF to work properly.

When I first read your post, I thought you were referring to the focus limiter switch, but that would not explain why the lens does not attempt to AF at all.

I can confirm your findings. It is a 7D issue. I can reproduce your results with the 70-200 2.8IS and the 100-400 which are all I had time to test. The 1D2 didn't have any problem getting focus from the extremities.

KennyG wrote in post #10643210
I can confirm your findings. It is a 7D issue. I can reproduce your results with the 70-200 2.8IS and the 100-400 which are all I had time to test. The 1D2 didn't have any problem getting focus from the extremities.

Do you recommend sending in the 7D for repair?

Any other thoughts, now that I got the thread moved into the camera section?

KennyG wrote in post #10643210
It is a 7D issue.

Really? Normally it's a user issue.
Check if C.Fn III-4-1 is set. If so, change it to C.Fn III-4-0.

The most common reason for this problem is that the user has changed that custom function from the default setting.

I do not have this issue with my 7D or any of the 3 different 70-200s I have access to. I haven't done much with my C.Fn settings so I'll bet it's a user caused error.

apersson850 wrote in post #10648701
Really? Normally it's a user issue.
Check if C.Fn III-4-1 is set. If so, change it to C.Fn III-4-0.

The most common reason for this problem is that the user has changed that custom function from the default setting.

I'll check my custom function settings when I get home.

I can assure you that it is how the 7D is handling (or not handling to be more accurate) getting focus when some lenses are at their focus extremes (manually set for the purposes of testing) and the subject is not at or near the extremes.

The CF 3-4 setting is very important to sports photographers. Let me get this right, you are suggesting to get around a problem with the 7D you should disable a very important feature? I'll say no more for fear of causing offence.

Let us know your findings

If C.Fn III-4-1 is set, the camera will not attempt to autofocus, if AF seems impossible all together. This seems to be the case when the lens is so far out of focus, that even the longest AF points in the sensor can't tell whether the lens is focused in front of or behind the subject, due to extreme defocus.

Okay! So I had CF III-4 set to 1, turning off the focus search. Turning it on (i.e. setting CF III-4 to 0) makes the lens AF when I set the focus to MFD or infinity and try and focus on something far/near respectively. Thanks for the help guys!