wrote:
I have a question for those of you that are very serious about
wildlife photography.

I currently own all Canon equipment and have recently started making
the move toward digital. My longest lens is the Canon 100-400 IS USM.
I am looking at purchasing a longer lens and am torn between the Canon
500mm f/4.0L IS USM and the Canon 600mm f/4,0L IS USM lenses. The cost
difference between the lenses on B&H's website is about $1,700.00.

Depends on which body your considering, the Rebel gives quite nice
results, and since the sensor is smaller then 35mm it has, effectively a
built in 1.6x multiplier, so 400mm, effectively becomes equal to about
640mm, in 35mm. This means you can get the extra length in digital for
no cost.

Paul