The Canon EF 1.4x III Extender mounts between your Canon EOS Digital SLR and a compatible lens (primarily Canon L Series lenses), extending the focal length of the lens by a noticeable 1.4x.

I got this without any great expectations, as a stopgap measure to extend my 70-200 f2.8 IS Mark III lens to a bit of a longer focal length - 280mm to be exactI did not want to buy a longer lens, my camera bag is full & heavy already. And I rarely need a lens longer than 200.

The extender does extremely well and is sharp for shots on a tripod. Where I ran into issues were on action shots and low light shots. I used the extender at my daughter's sporting event and had trouble with the focus because the extender slowed down the autofocus on my Canon 70-200mm lens.

If teleconverters were truly 1.4x extenders then Canon would surly go out of business because it would make no sense to buy longer focal lengths. Although I am no photo novice I had expected better quality photos and thus I can only offer this advice to you: If you are intending to have small prints...

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  Well constructed and extends your zoom by 1.4x. I paired this extender with a Canon 300mm f4 & Canon 6D and loved the reach (effective 420mm). I was able to capture some candid moments which would not have been possible with my 300mm

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  The photos I took looked great on the camera LCD and my 12in Surface pro 3 (2160 x 1440) but when seen on my 27" Samsung SB970 (2560 x1440) where I often display my photos at work I immediately noticed how terrible these photos were by comparison to my 300mm f4 without the teleconverter.

While there's much flack about the sharpness of extenders, even the EF 1.4x III, I'd say they were right. But wait!! I saw the same issue when attaching this extender to my 70-200 2.8 L II—slightly back focused on my 1DX2.

This is a great product. The photos are sharp and focusing remains quick and accurate (assuming lens compatibility). However, the final cost of additional reach is quite expensive and perhaps not worth the hefty price tag to gain that extra zoom unless it's exactly what you need.

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  quick, sharp focus, small, portable

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  expensive for the total value that it brings

Nearly double your range with your L glass zoom lens. A little pricey but very good quality.

Works beautifully with the 70-200mm f/4 IS, which is a very sharp lens to start with. I use it routinely for bird watching, using it with the 7D as a telescope to give about 5x magnification, and then blowing up on the screen for study in the hide, adding an extra 40% in linear size and 100% in...

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  No loss of IQ, no added CA to 70-200mm f/4 IS L

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  expensive, not massive increase in focal length

I use a Canon 7D with the 400mm F 5.6, which requires me to manual focus with the addition of the EF 1.4 extender. I am becoming better at manual focusing both with and without the extender attached, which to me is a plus.

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  Strong Construction, Consistent Output, Durable

I'm mainly using this extender with my 70-200 Canon L non-IS as well as the Canon 100-400 L. It works well with both, easy to fit and seamless functioning although one does have to get used to the extra length and weight.

Perfect with the Canon 2.8 70-200 for sports photo's. Great with the 5D III and 7D II.