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I can't get the 100 - 400mm L series and 2X Canon tele extender to auto focus.  Is this something that will ne manual only?  I recently purchased the Extender 2x III since it is "fully compatable"  Is there a autofucus mode that will work.  I have th...
My 70 - 200 f4 L IS continues to sound like it's running after acheiving focus and the picture is taken. Is this normal?
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