Summary: I was using a kit zoom and I was out in on a windy day, when I got home I noticed dust in the View finder. I took the lens off; I saw dust throughout my camera even on the sensor. I had to buy a new focus screen; the old one couldn’t be cleaned. I was lucky to have the equipment to clean the sensor, or I would have to send the camera out for repair. This lens is light and sealed to dust and rain drops. Very easy to use and at (2.8) it’s awesome.
Summary: The most used lens in my arsenal. This lens stays on my 40D most of the time. It is a great walk around lens and provides tons of flexibility when touring. I find that the image quality is superb and f2.8 speed allows for easy low light shooting. It's my Go-To lens and I've used it more than any other lens in the bag.
Pros: Versatility, tack sharp images, color & contrast, build quality.
Cons: Some say weight is an issue...I have not found it objectionable.
Conclusion: Since I traded the 24-105L for this lens, it's by far my most used lens. Sharp, fast, flexible, 24mm is great on FF. It's big and heavy, but that doesn't bother me at all (I shoot with a 1DM3 + 70-200 f2.8L IS for 16 hour days). The lens hood is genius, providing excellent coverage whether you're at 24mm or 70mm. I mention build quality as a negative, here's why.
Conclusion: Not as good as a good 24-85mm f3.5-4.5 .
Pros: Though heavy on a 1Ds it handles well and the hood protects against rain as well as against flare. autofocus is good and it balances well with my body
Cons: But, and it is a big but, I have so far had the use of four new ones, none of which is anywhere near as good as my 24-85mm f3.5-4.5mm. Curvature of field is so bad that it is like a magic lens. You can focus across a wide street at buildings on the other side, shooting down the street, and getting focus confirmation on the central AF point as usual, and where the point is focussed it will be sharp, but whereas my 24-85mm at 24mm will render everything in focus even at...
Summary: Bought this a week ago after a month living with the inferior 24-104 f/4 L. While the f/4 approached the look of the f/2.8 at the short end, there is no contest when looking at captures from the long side. Also seems like colors and contrast are much better through the 24-70. Another thing, even though both are designated "L" series lenses, the 24-70 is much better made, using more metal and less plastic that is used on the 24-105. Couldn't be happier.
Conclusion: I originally had the Sigma EX 24-70mm f/2.8 lens and found the image quality great for the price paid, however it did struggle with autofocus. I paid 3x as much for the Canon 24-70mm f/2.8L, and yes the autofocus was much faster, and while the image quality wasn't that much better than the Sigmas, the colours were cleaner and contrast seemed slightly better.
Pros: Contrast, flare, accurate AF, sharp at f/2.8, solid build
Conclusion: A real workhorse lens which won't let you down but also won't thrill the pixel-peepers. Would really benefit from IS. Range not really suited to 1.6 crop cameras IMO and performs better on FF/APS-H rather than the latest high pixel density smaller sensors. It's heavy for what it is but well balanced on pro camera bodies/gripped cameras.
Pros: Fast aperture, great colour and contrast, good bokeh for a zoom, built like a tank, useful range on FF and 1.3 crop.
Cons: Sharpness at f2.8 not up to the standards of Canons latest lenses, heavy, no IS. Must be due for a make-over soon.