Hi Ron,
this lense is known as the "Bigma" as it is a very heavy lens! I am looking at getting either this one or the 150-500mm.
I have read alot of reviews etc and it seems that a tripod or some sort of support is needed due to the weight of the lens especially if using it all day etc!
Recently I went to a local camera show where they had both lenses on show and the picture quality was very good from both lenses although the auto focus can be a bit noisy on the 50-500mm, I have also read about picture quality problems with the early 50-500 lenses but I mentioned this to the Sigma saleman that was there and this has been fixed apparently on the newer versions.
Will be interested if any one is using either lens and if you decide to get one would like to see some photos.
All the best
Andrew
Containership Admin