The Canon EF 1.4X II Extender Telephoto Accessory is perhaps the most "required" accessory for Canon telephoto lens owners.

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Product Description

Attaching this high performance Extender to a 135mm or longer lens, or to the EF 70-200mm f/2.8L boosts the focal length by 1.4 times. With five elements in four lens groups, it preserves the prime lens' image quality.

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Product Details

• Brand: Canon
• Model: 6845A004
• Dimensions: 3.70" h x 3.80" w x 4.40" l, .75 pounds

Features

• 1.4x telephoto extender for multiplying focal length of Canon 135mm or longer lenses
• Fits all 135mm or longer fixed focal length lenses and some 70-200mm telephoto lenses
• Preserves autofocus on any EOS camera when combined with f/4 or faster lens
• Weather-resistant construction and improved anti-reflective surfaces in the barrel
• Measures 2.9 inches in diameter and 1.1 inches long; weighs 7.8 ounces

Amazon.com Product Description
Multiply the focal length of your 135mm or longer lens by 1.4x without sacrificing image quality with the Canon EF 1.4x II extender. Optically superb, the lens fits all Canon 135mm fixed focal length lenses (except the 135mm f/2.8 Softfocus lens), along with the EF 70-200mm f/2.8L, 70-200mm f/2.8L, 70-200mm f/4.0L, 70-200mm f/4.0L IS USM, and 100-400mm f/4.5-5.6L IS zoom lenses. In addition, the extender doesn't sacrifice your autofocus on any EOS camera as long as it's combined with a lens having an f/4 or faster maximum aperture (the extender reduces the effective aperture by one f-stop). Best of all, this version maintains the outstanding optics of the earlier incarnation, but adds a weather-resistant construction and improved anti-reflective surfaces in the barrel. The EF 1.4x II extender, which measures 2.9 inches in diameter and 1.1 inches long, weighs 7.8 ounces.

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Customer Reviews

Another Good Canon Product
Got this to go with my 70-200L 2.8 IS lens which this is perfect for my shooting needs. Gives the added extension to the lens on my 5D and still maintains the image stabilizing and AF function. Canon did design this to fit only specific Canon lenses.
I tried it on my Sigma 50-500 and the outerbarrel of the TC will not fit inside of the Sigma.
Otherwise the TC was pretty sharp at least my copy is .

a little heavy for its size but works just great!
It comes with a little bag to store it in the gadget bag and as I said its a little heavy for its little size, yet it doesnt become a burden to carry at all. I am using it with a 70-200 f4L IS and the size of the combined lens looks quite long on a rebel XTi and of course draws attention to it. I dont notice any quaility decrease (on the pictures) when used with this lens, but anyway, im not using any lab equipment or pixel picking to really test that. The build feels solid and it fixes well to the other lens as if it becomes a part of it, I think thats what the intention is of course. The color of this extender is exactly the same as the 70-200 f4L IS which is not white but rather grayish, they both look beautiful together !

I highly recommend it since it does make quite a difference and overall it is a professional and very well developed pice of equipment. Im actually thinking on also having the 2x later on to achieve the 640mm with my 70-200L and a small sensor such as the XTi or the 40D.

Does exactly what it says
I only pair it with the Canon EF 70-200mm f/4L USM Telephoto Zoom Lens for Canon SLR Cameras and my Canon Digital Rebel XTi 10.1MP Digital SLR Camera (Black Body Only) at this point, but it has done wonderfully. Yes, it does cost me a stop of light (just due to the math on it), but I can't really see any quality difference between with and without. I also have the ability NOT to use it when I don't need it, which means I get a better lens at the short end of the range than I would have just getting a longer lens. I'm definitely looking forward to having other lenses to pair this with.