Summary: I have the Cosina version of this lens which is very sharp and have good contrast wide open at 400mm (even with my Nikon TC-16A tele-convertor) on my cropped sensor Nikon D70 body. This might not be the case if you use full frame camera.
Summary: I love this lens. That said, my first day out I was disappointed with the lens creep and it seems to have some vignetting though not pronounced in the final pictures. Tightening the ring made for less fluid zoom, still figuring this one out.
Summary: I have spent a lot of time in India's jungles trying to capture its wildlife as digital images. The results with my older lenses was always just mediocre. The Canon EF 100-400mm lens has changed all that. I am now getting beautiful images with lots of detail.
Summary: As an L rated Canon Lens, it performs as would be expected (SUPERB). This lens is HEAVY and it's because of the quality put into this product. The real intent of this lens is for OUTDOOR USE, and as long as you remember that you'll always get great results from this lens.