Question about Canon Extender EF 1.4x II Lens

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Canon Extender EX 1.4x ii not autofocussing

I have an EOS 40D with a 100-400 is usm lens. I just traded in my original EX 1.4x for a new EX 1.4x ii on the understanding that it would autofocus this lens. But it doesn't. Any ideas??

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  • johnnoR Feb 27, 2009

    I've just bought a Canon 100-400mm lens, and my Canon 1.4 II extender prevents the autofocus from working. Taping the three end terminals brings SOME autofocus, but not at the full extension (400mm) end. The camera (40D) 'hunts' while autofocus tries to function, but it generally fails. Approximate MANUAL focussing seems to help the AF complete the job - but this is not what I had anticipated for wildlife photography.
    Any comments would be appreciated.


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The EOS 40D only use auto focus up to aperture 5.6. Only the 1-series use auto focus up to aperture 8. The adapter adds 1 stop to the lens aperture. Since the 100-400 is a 4.5-5.6, the aperture range with the extender mounted will be 6.3-8.
There is a work around though. Just place a thin strip of insulating tape over the three pins on the lefthand side (lens side of the extender). No damage will occur to the camera or teleconverter. 
Canon Extender EX 1.4x ii not autofocussing - c9a9700.jpg

Posted on Jan 19, 2009

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