Thanks for the replies , seriously looking at the 50-500mm for use with my aircraft photographing hobby.

Not seen any of the other lenses apart from the 50-500mm in any shops yet.

Anyone using these lenses at the moment , initially considering the 50-500mm for use with K200D , but just found these other alternatives.

Anyone care to comment on the 15-500 or 120-400mm and share some experiences/views/examples of work

Thanks in anticipation

Andy