A great review
Andy Rouse has spent 6 months with the new EF 200-400 f/4L IS 1.4x and has posted a pretty extensive real world review.
“It is no secret that I am in the Shakira fan club, you know that by now. Its even less of a secret that I am in the 200-400 fan club, in fact I am a fully paid up lifetime member. I just love this lens. As you have seen above, I have really used it hard in a variety of situations during the 6 months I have had it, and it has simply done everything that I have asked. No failures. Nothing to complain about. I have inspected all of the images that I have taken for any distortion, chromatic aberration or lick marks and I can say, hand on one of my two Vulcan hearts, that I did not find any. And remember I have been using a prototype, your production ones will be mint.”
Preorder the EF 200-400 f/4L IS 1.4x: B&H Photo | Adorama | Amazon