I have bought this lens a forthnight ago with the intention of replacing my Sigma 50-500EX, whose sharpness I was no longer satisfied with. After a few months of research, coupled with my experience shooting airshows, I felt I needed a long prime to obtain a level of sharpness and contrast I could live with. I thought about the 100-400L and the 300 4L + 1.4x converter, but these were all compromises. The 100-400L, which Iīve used in the past, is not sharp at 400mm. And the 300 with the converter isnīt as sharp or fast to focus. So I went and bought the 400 5.6L.
Am I happy? You bet I am. If youīre shooting airshows in the US, for example, 400mm is the range most displays will fall into. Rarely youīll need to change your lens. And the 400mm is so light (compared o the Sigma, at least), itīs a joy to use it all day. Of course itīs not as fast as many would like, and it doesnīt have IS, but Iīm a daylight shooter. F/5.6 means a shutter speed, using ISO 200, of 1/2000 or faster. Add the 1.4x converter (a Canon, in my case), and you have a 560mm F/8 which will beat a 100-400L anyday without one! AF? I use the tape trick, so itīs no problem, although the AF will hunt sometimes.
And the quality of my shots now is much improved. Compare them with anybody using a 500mm 4.0 and you will hardly see any difference, except the subject will be a little further away. I know - Iīve done that already.
Highly recommended if you like airshows.