Excerpt: Used for sports and wildlife. wish it was lighter. This is everything everyone has said about it. Just marvelous. Seriously thinking of selling my 400 2.8 now that I have this. Need to read the book on some of the features especially vidographers.
Pros: Consistent Output, Fast / accurate auto-focus, Sharp, Strong Construction
Excerpt: Primary use is for nature/wildlife photography. Prior to purchase I considered and tested the EF 400 F2.8 and the EF 400 DO F4 lens. The high versatility of the 200mm to 560mm range offered by this lens was the major decision factor in purchasing this lens. I took delivery just before the peak of the spring warbler migration and have shot ~2000 pictures over the last four weeks. The picture quality is awesome and my ratio of quality shots has significantly improved.
Pros: Consistent Output, Durable, Fast / accurate auto-focus, Nice Bokeh, Strong Construction
Excerpt: I use this lens for all sports, and it is ideal. the zoom gives it great range, especially for football and baseball, and the built-in extender just adds to that. It's easy to operate, with all of the switches being easy to use without looking. As for the performance, it's the usual top drawer Canon quality. With this lens and the Canon 70-200, you can cover any field of play and any sport. It's a beast of a price, but if you are serious about your shots, it's worth it.
Pros: Consistent Output, Fast / accurate auto-focus, Nice Bokeh
Excerpt: This lens is amazing, delivery quality image as any prime lens, plus the feature that let you work in composition. This lens (200-400 f4) do the job of 200mm,300mm and 400mm primes 2.8mm. The only difference is the aperture (a little more than 1.2mm less of those three). Using late canon model cameras as 1D X or 5D Mark III, that is not problem. I feel this lens is a new generation of photographer's gear.
Pros: Consistent Output, Fast / accurate auto-focus, Lightweight, Strong Construction
Excerpt: Took it out immediately and shot with internal and external Extender(784mm-f13-1/1250-ISO1000-5DMkiii), I figured this should stretch the test. If I wasn't pleased it was going back! I kept it and am thrilled with the performance. The sharpness blew me away!
Summary: Excellent optics, beyond ridiculous price. This lens offers optics broadly equivalent to the Nikon 200-400 but costs almost twice the price. That is insane. Whilst with this lens you're stuck with a 1.4 teleconverter the Nikon can use up to a 2.0 and still autofocus using a d800 or a d4 and get, again, almost identical quality as with this lens using a 1.4 internal converter.
Conclusion: Best lens I've ever used for aviation photography. All of the versatility needed to capture images in any setting, and the built-in converter loses almost nothing I can detect in terms of image quality or focusing speed. Extremely sharp, extremely versatile, and built ruggedly for travel to rugged places.
Pros: Fast auto-focus, Superior build quality, Super-sharp images, very verstaile telephoto range, built-in teleconverter
Excerpt: Received a couple of weeks ago, have shot two NFL games. Still learning but immediate results are incredible. Moving from a 300 F2.8, I now have a range of 200mm - 560mm. Now I can cover the majority of the football (American) field and capture action in great detail. Paired with a Canon 1DX,it is the most flexible setup and the quality of image and build is incredible.The price is extremely high but if you can justify it, you will not be disappointed.