Sigma APO Teleconverter 2x EX DG Telephoto Lens Converter - Compatible with Sigma SLR Cameras - Extend Focal Length for Wildlife & Sports Photography

I don't get it how people that are too lazy to check compatibility are allowed to create negative reviews because their own mistakes.Virtually every one of the negative reviews on this item are because of incompatibility. There are a couple that say "it is supposed to work with my lens" but don't say which lens they are talking about. That makes the statement worse than useless.If you look at the reviews for Nikon and Canon teleconverters you will see the same comments (probably the same people). The description clearly states "select" Sigma lenses. Just as the Nikon says "select" Nikon lenses. So the Sigma TC is not designed to work with Nikon or Canon lenses and not all Sigma lenses will work. Go to the manufacturers site to check compatibility.Now to my review.I purchased this TC to work with my Sigma F2.8 70-200 lens as a lower cost solution to buying a longer lens for the occasions I needed one. Yes I lose some light for my D800, need to step down from 2.8 to 5.6. However that is the entire range from 70-200 (now 140-400). I find that in most situations I shoot that is way more than adequate because I do not use it for high speed photography. Unlike another reviewer I have noticed only a minor amount of autofocus degradation and the OS seems to work well but as always, the longer you go the more imperative it is to have a steady (tripod) shoot. Photographs are not 100% tack sharp but are very reasonable for the distance. In a recent airshow photo shoot I can see the pilots mustache clearly from about 200 meters through the cockpit. Not too shabby. Color saturation is a little down, almost on a par with a DX camera. But again the clarity is decent for a TC. I can tell little if any difference between this and a rented Nikon TC along with the Nikon VR2 70-200.This is a terrific value for the money if you know what you are looking for and buy it for the purpose it was intended for.