17-40 1:4 L Autofocus

[winminn]

Lens is sometimes very slow to autofocus and sometimes does not focus at all.  Any suggestions what could be wrong?

[kvbarkley]

What camera?

How much light?

[winminn]

Bright light with 7D Mark II

[ebiggs1]

"Lens is sometimes very slow to autofocus and sometimes does not focus at all.'

A better question is, has it always been that way?  Or, has it just developed that issue?

[winminn]

Has it always been slow and sometimes nonreponsive?  NO.

[jrhoffman75]

What is the subject? Does it have suffiecient contrast? Are you in One Shot mode? What happens if you arfe in A+ Green Square? Is it just this lens?

[winminn]

I have found that when the autofocus does not activate, it can help to point at something close at hand.  That sometimes helps, not always. If it "wakes up" from that act, then it seems to be okay.  However, it's still slowl

[Waddizzle]

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@winminn wrote:

I have found that when the autofocus does not activate, it can help to point at something close at hand.  That sometimes helps, not always. If it "wakes up" from that act, then it seems to be okay.  However, it's still slowl

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Just this lens, huh.  Some lenses do not transition well from focusing at near infinity, to focusing at near the MFD.  Your remark about “wakes up” is what brings this to mind.  Sometimes your subject can be the problem, like focusing on a bird sitting on a branch, hidden among other branches and leaves.

While the lens is what focuses, the camera body is what controls the shows.  Sometimes the combination of focusing mode, AF point selection, and other settings can degrade performance.  

You will get the fastest AF performance One Shot mode, which is what the Green [A] mode uses.  One Shot mode gives you a focus lock confirmation beep, while AI Servo does not.  

So, I ask what focus mode are you using?  Which AF point(s) are you using?

[ebiggs1]

"Is it just this lens?"

This is the next question.  In order to analyze this we need to go in a specific order.

[winminn]

Please suggest the specific order that I should undertake, per your suggestion.  Thank you.