Auto focus stopped on Canon 7D that I use with the new 100-400 mm telephoto and 1.4 teleconverter. ?

[elsciman]

I have used my new Canon 100-400 mm telephoto with a 1.4 teleconverter (II)quite happily for six months.  But all of a sudden the auto focus will not work with the teleconverter attached.  AF is fine without the converter on the camera.  What gives?  This is not an issue of low light because lighting makes no difference.  I did not drop the lens or the converter so I can't figure out why AF just stopped working.

[diverhank]

The 7D will not AF when the smallest aperture value is f/8 or higher.  When you add the teleconverter, the f/5.6 of the 100-400mm now becomes f/8 (1 stop loss) and the camera senses that and won't AF.,

If you want to be able to focus at f/8, you can fool the camera by taping some of the pins on the teleconverter.  You can search the internet for instructions on how to do it. 

[elsciman]

diverhank,

      Thanks for you quick reply.  But your answer does not explain why auto focus with this camera combination has worked flawlessly for me in a wide variety of light conditions for the past six months.  Auto focus did work.  My question is why would it suddenly stop working.

elsciman

[diverhank]

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@elsciman wrote:

diverhank,

      Thanks for you quick reply.  But your answer does not explain why auto focus with this camera combination has worked flawlessly for me in a wide variety of light conditions for the past six months.  Auto focus did work.  My question is why would it suddenly stop working.

elsciman

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It shouldn't have worked at all if you've been using the Canon TC.  Non-Canon TC doesn't report the aperture so the camera is fooled by design.  For Canon TC, it is possible that you haven't used the lens at the 400mm end  where the f/stop is at f/5.6. below a certain Focal length, the aperture is f/4.5 and that might work with the TC.  Also, are you sure your TC wasn't taped up before by someone else (if you bought it used) and now the tape has fallen off?

[Waddizzle]

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@elsciman wrote:

diverhank,

      Thanks for you quick reply.  But your answer does not explain why auto focus with this camera combination has worked flawlessly for me in a wide variety of light conditions for the past six months.  Auto focus did work.  My question is why would it suddenly stop working.

elsciman

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Which focus points have you been using?  The center point is the most sensitive [highest f/stop].

[TTMartin]

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@elsciman wrote:

diverhank,

      Thanks for you quick reply.  But your answer does not explain why auto focus with this camera combination has worked flawlessly for me in a wide variety of light conditions for the past six months.  Auto focus did work.  My question is why would it suddenly stop working.

elsciman

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If you didn't change teleconverters, then perhaps you were using a 'taped' teleconverter (Google it), and the tape wore through or got knocked off.

[elsciman]

Thanks guys,

    Mystery solved!  I cleaned the contacts on the converter and the camera with some lens cleaner and now the Auto Fous is working okay again.  

    Thanks for your help,

    elsciman

[diverhank]

Is your camera 7D mark II? There is a big difference. The Mark II can AF at f/8