The 24-70mm f/2.8L is arguably one of the best wide aperture zooms ever built. It has silent fast ring USM focus, a large 77mm front element, and a solid construction (and weight like a brick!). These tests are by no means definitive -- While Canon's quality control is quite tight, I wanted to test my copy of this lens to see if it had any blaring defects.

I used a Canon 1D (Auto White Balance mode) on a tripod with autofocus and 2 second timer delay to prevent shake. The purpose of using the autofocus was to test the consistency of the focusing. Due to errors in focusing consistency, some (very few) pictures came out of focus (OOF) and were useless for comparing sharpness. Overall, the autofocus reliability was excellent.

Canon EF 24-70mm f/2.8L -- Near Focus (~0.5m)
f/2.8, 24mm	f/2.8, 70mm
f/3.2, 24mm	f/3.2, 70mm
f/3.5, 24mm	f/3.5, 70mm
f/4.0, 24mm	(f/4.0, 70mm -- OOF)
f/5.0, 24mm	f/5.0, 70mm
f/6.3, 24mm	(f/6.3, 70mm -- OOF)
f/8.0, 24mm	f/8.0, 70mm
f/11.0, 24mm	f/11.0, 70mm
f/16.0, 24mm	f/16.0, 70mm

Notes on Near Focus

24mm:
• Seems to be quite good from f/2.8 onward.
• I can't explain the color shift toward magenta at f/5.0 and above except to attribute it to the auto-white balance algorithm.

70mm:
• Slightly soft at f/2.8, but razor sharp above f/3.2
• Almost no shift in the AWB color.

Canon EF 24-70mm f/2.8L -- Far Focus (~3m)
f/2.8, 24mm	f/2.8, 70mm
f/3.2, 24mm	f/3.2, 70mm
f/3.5, 24mm	f/3.5, 70mm
f/4.0, 24mm	f/4.0, 70mm
f/5.0, 24mm	f/5.0, 70mm
f/6.3, 24mm	(f/6.3, 70mm -- OOF)
f/8.0, 24mm	f/8.0, 70mm
f/11.0, 24mm	f/11.0, 70mm
f/16.0, 24mm	f/16.0, 70mm

Notes on Far Focus

24mm:
• Hard to comment on the sharpness since they all look identical! I probably should have used a more sophisticated pattern for the pictures. Next time...
• Again, seems to be a slight magenta color shift that is somewhat erratic - Probably due to the external AWB sensor on the 1D for some reason.

70mm:
• Slightly soft at f/2.8 to f/3.2.
• Noticeably sharper at f/3.5 and higher.
• No perceptible shift in the AWB color.