[Johnny Brown]

You're fucking kidding? £450 is not a reasonable price for a converter.

[dave]

It probably is given the lenses its intended to be used on.....I.e. if you're dropping 3 kubricks on a 300mm 2.8.

[Tris]

You're fucking kidding? £450 is not a reasonable price for a converter.

Exactly, my reaction too 

I ended up buying a Tokina 400mm for £60 off Ebay in the end..

[Johnny Brown]

Back of the net!

Dave, it probably isn't given the old one costs half that. I bet its not twice as sharp.

[Tris]

I thought it may be brought out so that you could autofocus with the BIG telephotos like the 500mm's and the 600mm's, but no - comparing the old and new compatibility charts they are identical.

The only difference seems to be:

Aspherical Lens Element
Virtually eliminates coma and other aberrations, especially at wide apertures.