Summary: Reviews I had read were very complimentary about the optical quality of this converter, but I my experience was different. I wanted the converter to extend the coverage of my 70-300L for long distance, for surfing, whittles, boards, etc. I was aware that automatic focus would be questionable and it was. What I did not expect was a noticeable loss in sharpness and color saturation. I tested it by taking photos of a scene at Honolua Bay with and without the converter.
Summary: Truthfully, I haven't used the teleconverter much yet, but I hope to soon. I bought it because so many reviews I read were really taken by its ability to deliver sharp pictures and its significantly lower cost.
Excerpt: Use it with my 100-400L. It does not seem to degrade the image at all. It does cause my 7D to hunt with the lens unless there is high contrast and lots of it. Lots of light is needed also to get AF. BIF do not seem possible.
Summary: I do mostly bird photography and bought the Kenko 1.4 X to go with a Canon 70-300mm f4/5.6 IS USM lens and Canon t4i body. Unfortunately, with the teleconverter installed, the autofocus would not lock on the subject and stay. A great deal of time was spent with the AF searching and not locking. I tried manual focus but found the images just weren't sharp enough with the teleconverter attached so I returned the unit to Amazon.
Mediocre Extender but still produces usable images.
11 December 2013
Summary: I bought this for a college baseball game I was covering. Although it worked, the quality was mediocre. I wasn't that impressed with the results but they weren't terrible either. I am extremely picky when it comes to my photography, especially for my clients and although I say the image quality lacked, the images were still usable. I'd honestly recommend going with the Canon extended if you are willing to pay the money. If you're in a crunch, go for this one.
Summary: After reading a lot of stuff about which lenses are supposed to work, and not work, with which teleconverters, I was delighted to find it works with both of my Nikon zoom lenses, the 28-200 DX format and the 80-400 FX format. Took a chance and found a winner.
Excerpt: After dealing with Nikon tech support (equivalent to no support) I bought a Nikon teleconverter which was incompatible with my lenses. This was after spending much time with Nikon tech & having them tell me that the lenses were compatible. I sent the Nikon back & bought the Kenko which solved my problems, is a quality product and is easy to use. I recommend it.
Pros: Durable, Easily Interchangeable, Fast / accurate auto-focus, Lightweight