I'm looking at getting a super telephoto lens and was looking for some feedback from those of you who have used them. I currently own a 300/2.8 and have been using it on the 7D with the 2x III to photograph wild ducks and small birds. However, I would like to have a little more reach, since I find myself cropping extensively. I was thinking with the 600/4 + 1.4x I could get 840mm or with the 400/2.8 + 2x I could get 800mm. The 600/4 seems like the right idea, but the added versatility of the 400/2.8 is enticing (not to mention that the 400/2.8 is a little cheaper). I don't shoot sports often, and when I do the 300/2.8 is usually sufficient. The weight of the two is essentially the same, but the 400/2.8 is a little shorter than the 600/4, so maybe it's a little easer to carry?


Looking forward to hearing from those of you that have used one or both of these lenses.