90D focusing problem at 400mm w/Tamron 18-400 lens

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steinr98 Regular Member • Posts: 442
90D focusing problem at 400mm w/Tamron 18-400 lens

My 90D wii not focus lock at 300-400mm on a Tamron 18-400 lens.  This lens works fine  on my 7D MKII / and a friends Rebel 7i.  My Canon 70-200, and 100-400II both work perfect at any focal length on my 90D.  In the book(for those that still read the book) it does say, if there is not good contrast, the 90D my not focus well!!!  The Tamron 18-400 works fine on the 90D at 18 up to 200mm and then quits.  Any one experience anything like this?  My thoughts are that the Tamron at over 200mm the contrast must be weaker.  I do know that if you add a 1.4/2.0 extender to a telephoto lens the contras will suffer "Sum" but not much.  I do know that "Marvin The Mavin" does report that some lenses will not work on the 90D -

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Steinr98

 steinr98's gear list:steinr98's gear list
Canon EF 50mm F1.4 USM Canon EF 70-200mm F4L USM Canon EF-S 18-55mm f/3.5-5.6 IS Tamron SP AF 17-50mm F/2.8 XR Di II LD Aspherical (IF) +3 more
Canon EOS 7D
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