Excerpt: Bought this to go along with the Sigma 120-300 2.8 Sport. Mounted on my Canon 1D IV, I have found it to be very fast focussing and I love the extra reach the 1.4x gives. I won't lie, it's not as fast as a Canon 300 2.8 v2 mounted straight onto a 1DX, but for most shooters this converter isn't going to slow you down much, and who doesn't love getting extra length out of a lens.
Summary: This was a hard to find item. Sigma has discontinued it. I have their 180 f2.8 macro lens for which this converter is used. It works well. Some, but very little drop in resolution. I have other converters, but wanted this one to match the Sigma optics of my macro. It was a good choice. It is small, light, and reasonably priced. Puzzled about why Sigma would discontinue it.
Excerpt: This converter is excellent with my Sigma 150-500 lens. I am still working with some of my manual setting. I have gotten several excellent images. I do have to mount on monopod for stability..
Excerpt: Some times the 2x is too much light loss. The 1.4 is the answer. As a birder using this combined with the Sigma 120-400 gets me close without sacrificing f-stops. The fit and finish is world class. I look for this being a manufacturing engineer. I am using this on a Nikon 5200. I loose AF but knew that before buying. This is not an issue because I am more comfortable in manual with distance shots. I recommend making the purchase.
Excerpt: Works Great. expect to take some time with your camera "autofocus fine-tuning" to get the best results, I suggest the slanted yard-stick around the distance you expect to shoot. Great results for birding with the 120-300 f 2.8 Used it with 500mm in manual focus.
Excerpt: If you aspire to use this on Sigma's own APO 500mm f/4.5 EX SG HSM on a Canon body, then be prepared to focus manually. Neither the Sigma or the Canon Extender EF 1.4x III will give you AF, but what you lose in focussing speed, you pick up in image quality. I can't see any noticeable loss when using the Sigma converter, unlike its bigger 2x brother which I would give a wide berth. Excellent value for money, but be prepared to shoot retro style i.e.
Excerpt: I'm not sure if I've used it for it's best purposes but it does what it's suppose to do and that's get in closer without buying another lens. Just wish it was as sharp as using your lens itself! Not bad, but not over the top great!
Pros: Easily Interchangeable, Fast / accurate auto-focus, Lightweight, Strong Construction