Little to add to the above reviews except to say that I trekked around the Alps for a month with this lens - something I wouldn't have done with the f4 500L. Lack of IS is listed as a "con", but IS would add to the weight in an unacceptable way for my needs. And when attempting to hit birds in flight, my shutter speeds are high enough to keep the image sharp (generally!)
I've used the 100-400 zoom, and found the IQ wasn't as good as this lens - and I was using it at 400 for the majority of the time. Given the reported dust issues with the zoom, this prime is my weapon of choice. (I couple it with the 70-300L.)
With my 7D, this gives a reach of around 640mm. the AF problems with teleconverters don't worry me: given the pin-sharp IQ, heavy cropping is likely to give the same results.
I've used the 100-400 zoom, and found the IQ wasn't as good as this lens - and I was using it at 400 for the majority of the time. Given the reported dust issues with the zoom, this prime is my weapon of choice. (I couple it with the 70-300L.)
With my 7D, this gives a reach of around 640mm. the AF problems with teleconverters don't worry me: given the pin-sharp IQ, heavy cropping is likely to give the same results.