EF 16-35 f4 won't stop AF hunt with lens cap on

Started 1 month ago | Questions thread
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Peter Kwok
Peter Kwok Senior Member • Posts: 2,462
EF 16-35 f4 won't stop AF hunt with lens cap on

My 16-35 F4L IS when attached to my EOS R via an adaptor would keep changing focus from infinity to MFD and back once a second or so.  My R is set to single point one-shot AF, and I am not touching any button.  After I remove the lens cap, it would stop, as if it is focus on something.  As soon as I put the lens cap back on, it would resume hunting again.

With the lens cap on, it just keep moving its focus back and forth until the R shuts off to save power. This happens regardless whether IS is on or not.  If I switch to MF on the lens, then it would stop.  But as soon as I switch it back to AF, it resumes hunting.

My 70-200 f4L IS would not do that.  Neither would my new RF 24-105L.

I cleaned the lens and adapter contacts. That did not help.

What is causing the problem? Did I missed some settings? Please help.

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Peter Kwok
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Canon EOS 5DS Canon EF 16-35mm F4L IS USM Canon EOS M6 Canon EOS R Canon EF 24-105mm f/4L IS USM +7 more
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