[Stevelphoto]

I've heard a lot on this subject and was talking to a pro about it not too long ago - it seems a popular subject, because people want the reach without the price/weight of a 500mm. The verdict was that the 2x converter can perform well, but is best suited to getting a bit closer in to a bird you are already close to - rather than using it over larger distances, where the image could easily deteriorate.