I have been waiting on these lenses for some time. My question on deciding which to go with was which would give me the longer focal length using an extender, and still give IQ good enough to be acceptable.

It appears that the 500mm will be able to give decent IQ at 1000mm, and the 600mm will not at 1200mm. In some ways this makes the 500mm the longer acceptably usable lens.

Thoughts?

http://www.the-digital-picture.com/R...mp=2&APIComp=0