Summary: I'm very impressed with Kenko's 2.0X Pro Teleconverter. I've shot over 650 photos with it on Nikon's d800 with Tamron's 200-500mm telephoto lens and the results were excellent. I did have a little trouble using auto-focusing at first, but what I thought were out of focus were actually in focus, and...
Excerpt: Before buying the Kenko, a couple of different Canon teleconverters were tried and not certain whether it was my lens (EOS 70 - 200mm), camera body (D5MkII), the devices, or combination and most shot were simply not sharp or as vivid as expected.
Summary: Great product for the money. I've used it several times now with 5D MKII and Tamron SP 70-200 2.8. As everyone says, there is a little image degradation but as long as you shoot stable and don't crop a lot, you'll come away with some nice shots. Focus response is good, IS is good.
Summary: A very good doubler for a good price. Constructed using Hoya glass. Auto focus was a little iffy from f11 or higher but it does work contrary to product information. Resolution looks good with clean edges with my 100_400 L glass Canon lens. Would recommend this to anyone.
Summary: Not bad for the price compare to the Canon, I bough it to use with Canon 70-200 f4 Slow and sometime fail to focus, even use with 50 f1.8 reason are the same, the glass not so sharp as I aspect, might be useful with still subject and manual focus.
Summary: This may work for someone else. The build quality was OK, but I found pics to be noisy when using this glass. Returned the product for a refund. Used with a Nikon D7000 and a Nikon 80 to 300 lens.