Sigma APO Teleconverter 2x EX DG for ...- User Rating: 
Summary for Sigma APO Teleconverter 2x EX DG for ...- Very Nice, and Useful Accessory
Notes on Sigma APO Teleconverter 2x EX DG for ...- overall, i like this teleconverter. I use this with the new sigma 70-200mm F2.8 II lens for Rebel XTi. the F-stop became 5.6 with teleconverter, but i get up to 400mm zoom, which makes quite a difference. While it's true that most of my pictures came out soft, but some pictures came out quite sharp- so it may just be me. there is some slight color distortion, but it's only more noticeable when you shoot macros.
i glad i got it. and it has allow me to extend my lens from 140-400mm, of which 200-400mm is a critical range for wildlife and sports.
Update: July, 08
Okay, after a couple months of using Sigma 70-200mm F2.8 EX II lens, I found out that the Macro function is almost useless because of its such poor quality (soft focus and CA)- so the F has to be 9 or greater...now when you add this Teleconverter your F number is going to be even higher (i found the sharpest image at F22!!).....lowest i try to get an usable image is around F15 or more. Now this is macro.
Just make sure you have plenty of light, and that the subject is far away and then this will be a great add-on for you.
UPDATE:
I originally bought this for my Sigma 70-200mm F2.8 Lens- and i really doesnt like its performance at the low F-stop (blurry, ca, and other problems), but i just got the Canon 70-200mm F2.8 IS lens (and yes, it's much better than the Sigma!), and is pleasantly surprised to find out that this teleconverter works with it! in fact, the pictures came out better than the Sigma lens- so I think the picture quality issue is because of the lens not because of this teleconverter.
overall, you're still going to get the best picture quality without this teleconverter, but with 2x and Canon, I think this will produce a better picture than any 70-300mm lens out there.
Sigma APO Teleconverter 2x EX DG for ...- User Rating: Summary for Sigma APO Teleconverter 2x EX DG for ...- Affordable and quality
Notes on Sigma APO Teleconverter 2x EX DG for ...- I've used Canon lenses, Tamron and Sigma. All are fine products. For my money I have found that Sigma works well, without the high cost of Canon.
Currently, I'm using my extender with a Mark III and mainly my f2.8 70-200mm Sigma lense. I'm mainly shooting High School Football games with this combo & my Turbo 2x2. It's working out beautifully! I would highly suggest the Sigma line of lense, esp if you're on a budget.
Sigma APO Teleconverter 2x EX DG for ...- User Rating: Summary for Sigma APO Teleconverter 2x EX DG for ...- Sigma APO Teleconverter 2x EX DG for Canon Digital SLR Cameras
Notes on Sigma APO Teleconverter 2x EX DG for ...- Not compatable with Cannon lens only select Sigma lens.
