I'm not advocating jumping ship from the 70-300L per se, but I have shot with my 100-400 on bodies ranging from entry-level Rebels up to a 7D now, and while it is no EF
.8, I have never hesitated to zoom out all the way out to 400mm for a shot. Assuming you have it stopped down a bit (F7.1-F9
) it has always done just fine for me. I know some people have had issues like crazy with their copies, and I was one of them for a while, but after micro-adjusting the AF
, I was golden.
I have heard the 70-300L is quite nice however. Don't bother with converters on the 100-400, it's a lost cause. You're better off getting a EF
400mm F5.6 and cropping at that point, which I did when the 100-400 was misbehaving, although I rarely use it nowadays