Probably wildlife photographers. I think it would be too long for sports. I have the 600 & 800 f/11's and they are more than sufficient for my needs, but there are some who always need a little more reach.
Jim
Seems as if there never enough reach when shooting small animals/wildlife. I always had my 2X on my 400mm and now the 100-500 and there are times where I want to frame even tighter. Certain situations just don't allow you to mover any closer without scaring off the subject or having to take a swim!
1200 and 800 are specialty lenses. I've had the 800 and find the 600 much more flexible. With 1.4x and 2x it give you about the same. Magnification only helps to the point where atmospherics degrade the image too much. These lenses to me are limited to small song birds that are fairly close.
