Excerpt: It might just be a problem with the new 5D MKIII but unless you are setting exposures entirely manually it is very problematic. It grabs the brightest spot in your frame and adjusts to that so you end up with sometimes with as much as 90% black silhouettes and blobs and then 10% of properly exposed blue sky and white clouds peeking through tree branches.
Pros: Durable, Sharp
Cons: Exposure problems, Metering Problems, Poor in Low Light
Conclusion: Very soft at F4, only ok at 5.6, sharp at F8, F11. For the L Lens hype and the price I expected better. My 18-55 kit lens is as sharp and in some cases as at F4 sharper. The lens was replaced the same week I bought it and the second one was the same. I got the money back.
Excerpt: Unfortunately, I have to write my first negative review for a canon lens. I bought this lens to replace my canon 17-85mm. I was very disappointed when I saw that L lens is actually performs worse than my 17-85mm. 17-40mm is unexpectedly soft at f4 both in the center and corners. My 17-85mm is considerably sharper at the same focal length and aperture. 17-40mm is little better at f8-11, but only in the center, while corners are the same quality as in my 17-85mm.
Pros: Durable, Fast / accurate auto-focus, Lightweight, Strong Construction
Excerpt: I purchase this wide angle lens for landscape photography with the 5D markii. After reading all the good reviews I decided to give it a try. I was very dissapointed. My images came out soft even in the center. [...] I'm wandering if I ended up with a bad copy! I ended up ordering the Carl Zeiss 21mm distagon 2.8 and the result are much superior. I still want an ultra wide lens and plan on ordering the 16-35mm 2.8 in the near future.
Conclusion: I have owned this lens for several years and use it to shoot kitchen interiors. Shots are often tight with the need for wide angle. I bought this over the 16-35mm due to the price. However kitchens are full of linear / vertical geometry and we shoot parallel and level. Unfortunately this lens has tremendous distortion along the perimeter of the shots. It is especially noticeable in our work since we are always aligning our shots with vertical lines in the room.
Conclusion: I owned this lens for quite a while, but rarely used it because the image quality was not acceptable. This would be a very useful focal length / range and it is too bad that it is not at all sharp.
Conclusion: i got this lens 3 days ago and i was testing it heavily on my canon 40d camera. i have to say that i love the built quality and quiet and fast usm. the problem is that my lens didn't produce sharp images at all. i shoot in raw and i had to correct sharpness on every single photo. i tested this lens shooting landscape and then at home on tripod comparing it to canon 18-55 kit lens that i got for £35 second hand. there was no or very little difference.
Excerpt: I bought this with some hopes of getting some extra wide angle reach. I was not impressed with the optical quality. The lens was soft wide open and stopped down at all focal lengths. In all cases the IQ (image quality) of this lens was softer then my cheap $100 canon lens and was also comparable to my other off brand lenses that were 1/3 to half the price. The sweet spot on my copy appeared to be f/8 but it still didn't sharpen up more then my cheaper lenses.
Conclusion: I have been quite disappointed in the quality of images produced by the 17-40mm L USM lens. With the L designation, wide-angle optics, and the lofty price, I'd expected tack-sharp image quality. Instead I receive fair to poor results whether focused manually or automatically and over the full range of zoom focal length. Making matters worse, I cannot locate ANY reference to Canon Warranty support on this Web site. Now both disappointed and angry.