This lens is legendary. All the pros and semi-pro photographer have one. This is a big and heavy lens to use and carry around. It’s also one of the best lens to use because of the 2.8 aperture. The bokeh is buttery smooth. I still have a love hate relationship with this lens.
First of all, this is an awkward lens. There are a lot of bad copies out there. The problem was that it either back focused or produced really soft images. The lens also reverse zooms. The lens extends at wider angles. When I use autofocus on a 50D and a 5D mark 3, it’s hit or miss. Sometimes I would get good sharp images. Other times, it’s a blurry mess. I would say it’s 50/50. Manual focus is a different story. This lens need to be manual focused.
Unfortunately, the original version of this lens has been discontinued by Canon. There is a newer version out that corrects a lot of the flaws. It’s also slightly lighter and smaller. Only slightly though. The big barrier to the average consumer is that this lens costs $2300. For that kind of change, I would rather get the 70-200mm f2.8 II.