Summary: This is perhaps Canon's worst L series lens. Heavy, slow to focus and as an F4 not particularly good indoors. We tried to get ours to be of service in our studio or on location but found ourselves going either to Canon's 24-70 2.8, the venerable 70-200 2.8 or the 85 1.8.
Expensive to repair. Poor design of aperture flew cable.
Frank Burns, Amazon
5 August 2015
Summary: Great, until it broke. Love the lens, but $500 to fix a lens due to a $25 aperture cable breaking is ridiculous. These lenses are prone to this cable breaking due to poor design of the internal aperture flex cable. It will probably eventually break due to zooming and unzooming, like mine did.
WARNING -- COMES WITH YOUR OWN SCRATCH/CRACK INSIDE THE GLASS.
2 May 2015
Summary: I think they are selling defective items. I bought this to take on a trip and admit I didn't expect well when I got it. As soon as I started taking pictures, I noticed there was a spot on all my shots.
Summary: Buyers beware of the "White Box". I purchased mine and it was defective (very slow focus). It turns out most white box units are either refurbished or not under warranty. I had to pay an extra $300 to Canon to get the focus issue fixed and it was not 100% sorted out.
Excerpt: The lens exhibits the worst barrel distortion I have ever seen on ANY lens. Unless you want to spend all your time squaring up images in post, avoid this lens. Canon has a lot of nerve putting the L glass brand on this lens. The EF 28-135 that came with my 40D is much superior.
Excerpt: i think this is a great lens if you know where it fails and don't need it for those uses.
1. no matter what some reviewers have claimed, this lens will not shoot all that well fully open at night or in low light. at best i'd say at f 4 this will give you fair to middling resolution. 2.
Pros: Superior build quality
Cons: bowed perspective, fair at best sharpness fully wide open aperture
Excerpt: I just purchased the 60d and the Canon L series 24mm-105mm lens. My first shots were indoors and all using the flash. The lens worked great but all of the pictures had a dark semi-circle in the middle of the bottom of the image.