First things first: this only works with certain lenses. Sigma publish a compatibility list on their website, so check that first. If you try and mount an incompatible lens on this, the protruding front element might grind against the back element of your lens and cause damage. I use this with the Sigma 70-200mm f/2.8 APO EX DG HSM Optical Stabilised Telephoto Lens Canon Fit. It works wonderfully on both my cropped sensor and full frame sensor bodies. With the teleconverter, the length is increased to 98-280mm, which on a crop sensor camera is the equivalent of 157-448mm when taking the 1.6 x crop factor into account. I haven't spotted any impact on image quality, neither does the autofocus speed or accuracy seem any slower. So it does exactly what it says with no real compromise except the fact the maximum aperture is reduced from f2.8 to f4 (par for the course with teleconverters). Great bit of kit. Also comes with front and rear caps and a good (if slightly oversized) lens pouch.

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This teleconverter is poor. It degrades image on prime lenses to a degree where you would only want to use it if it meant getting a shot as a last resort. Movement between camera and teleconverter is terrible. Don't buy it!!!!!

Build quality Price

Unacceptable loss of sharpness and contrast when used with my Sigma 400mm lens Too much play in the connections when mounted

Since this is the only teleconvertor I've used, I have no basis for comparison against others. Only used in conjunction with my Sigma 400mm f5.6 lens. This lens is quite sharp and contrasty by itself, but with the 1.4x teleconvertor, sharpness and contrast is noticably degraded. I was prepared to lose about 10% off the sharpness and contrast of the 400mm lens, but actual results seem to indicate greater than 10% loss. Either that or I notice shapness and contrast loss much more than others. Doesn't autofocus with the 400mm lens, but that was taken into consideration when purchasing. There is a too much play in the physical and mechanical connection between the lens, teleconvertor, and camera body, requiring me to be carefull when flexing or panning the combo when mounted on a tripod. Maybe I just got one where quality control slipped up. Only use now as a last resort when getting any shot is better than getting no shot.

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No loss of autofocus speed No loss of sharpness No loss of contrast in the image it helps to produce. Solid made like a rock

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A real surprise in that not only was it every bit as sharp a result as the Canon equivalent, but afforded NO loss of focus lock as the Canon is known to do. Sharp edge to edge with on either a 180 APO Sigma macro lens or a 100-300 APO F4 EX HSM lens wide open. No small feat. No noticable difference on or off in sharpness or contrast of the image.

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Canon 1.4xII Teleconverter

Superb optical quality (with Nikon 80-200/2.8D and 300/4), tack sharp edge-to-edge.

Quicker AF speed, even with my older non-AF-S lenses, than the older Tamron AF-D 1.4x teleconverter.

Build quality appears very good.

Flare control is very good too; sometimes when you add a tc (with its additional glass surfaces) you can create or compund problems with stray light. Not so with this one.

Not so much a weakness as something to be aware of: this tc is designed for telphoto lenses. So, while it is optimized to deliver outstanding results with big glass, it will not mate with most other lenses, including many telephoto zooms.

The front element and element housing protrudes, making this teleconverter work only with lenses with recessed rear elements - and not all of those at that. For example, the Tamron 70-300/4-5.6 LD has a deeply recessed rear element, but it won't mount. The Sigma teleconverter works well with the Nikkor 300/4 and 80-200/2.8D, providing a superb autofocusing 420/5.6 and 112-280/4. It provides visibly better optical performance than the older model Tamron 1.4x AF-D teleconverter with both of these lenses, and marginally faster AF as well. This is not saying much - AF with the 300/4 + 1.4 EX is leisurely. AF with the 80-200/2.8D + 1.4 EX is adequate for slow-moving subjects and adequate for tracking medium-fast-moving subjects, but not up to finding and locking onto fast-moving subjects. If you need fast AF, you need to pair this teleconverter with the AF-S versions of these lenses. Build quality and optical quality are first-rate; the Nikon 80-200/2.8 + 1.4 EX is sharper (but more-cumbersome) than the very competent Tamron 70-300/4-5.6 LD; the 300/4 + 1.4 EX is shaper than most 400/5.6 primes.

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Emailed query was answered quickly.

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Tamron .4x AF-D tc (fits any lens, not up to the quality of the Sigma .4x EX with the longer glass).

Nikon TC-14b (no AF but *the* standard for optical quality - I think the Sigma 1.4x EX comes very close, though, and adds the convenience of AF).

Superb quality for a converter

Protruding front element

I bought this at the same time as a Sigma EX 70-200 f2.8. They are a great partnership. Optical quality is surprisingly high, and for the crazy price I paid this is an absolute steal, even if I daren't use it with any other lens, because of the protruding front element.

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Vivitar 2x and many others

Optical quality & build

Autofocus incompatibility w/Nikon lenses

Excellent results for an inexpensive T/C works well on the Nikon 300mm f4 but does not autofocus on my lens. Called Sigma and they state it should only be used with Sigma lenses for reliable autofocus operation... other lenses may not work properly. (This is also clearly spelled out in their instruction manual - watch out for claims by retailers such as B&H who say it will autofocus --- mine does not!!)

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