Tamron AF20C-700 Review: Tamron AF 2X Teleconverter for Canon Mount Lenses. I purchased this for astrophotography purposes, I'm using it with a Canon Rebel XSi (EOS 450D).As the description says, using this costs you 2 stops. Autofocus has been hit and miss for me; my 50mm prime searches a bit, but usually focuses fine. My Tamron 70-300mm Di LD lens won't autofocus at all.Quality-wise, I get noticable purple fringing in some images, but nothing that's uncorrectable.I'm definitely recommend this to anybody searching for a cheap teleconverter - If you want quality though, get the Canon version.13 of 14 . Read more »
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