1 out of 10 points and not recommendedlarge apertureslow focus, on 40D at 24mm casts shadow when flash used, you have to hunt for a good copy, manual focus ring too coarse, two switches required to engage/disengage manual focus
I just purchased this lens two days ago and got a bad copy. First it had front-focusing issues missing for as much as 9cm from the focus point. I sent it to calibration, they calibrated it to my 40D so it didn't front-focus that much anymore but it still kept missing the focus in 9 out of 10 shots. When it misses the focus that is clearly visible in viewfinder -- it tries to hunt it rapidly moving the elements as if the the seek step is too large to hit the correct spot in the middle and it ends up missing it in either direction. It is totally unusable except in manual focus mode and even then the manual focus ring is too coarse. I have sent it back for a replacement, will get the new one by the end of the month.reviewed August 16th, 2008 (purchased for $535)
Needless to say I am extremely pissed off by this, because I bought it specifically for my trip to San Francisco tomorrow, I got severely inconvenienced by having to bring it to the service center and I spent at least an additional $50 on cab and phone calls to camera dealers and service center not to mention the time and nerves wasted in the process.
To summarize, I paid what I believe is a fair amount of cash for a lens and I expected it to be at least acceptable right from the start.
Instead, it ended up giving poorer results than a plastic 3mpix fixed focus point and shoot camera which goes for less than $100.
When I get the new one I will post another review here, but until then I advise everyone not to buy this lens unless they can test it in the store before purchasing it.
I have given up on this lens because I couldn't wait another 20 days for new shipment.
If you are seriously considering it then you have to ask for at least three pieces and test them thoroughly in the store to pick the one that works reliably and is sharp.
Another thing to consider is that on Canon 40D when you zoom out (24mm) and the lens goes fully out you can't use flash because it casts the shadow. You have to zoom in to ~35mm to get rid of the shadow. On APS-C sensor that is actually 56mm and you will find yourself hitting your back against the wall very quickly.
Overall build quality doesn't seem too bad, but when you zoom in fast you can feel that the lens is pumping air out. At least the copy I had did that.
Conclusion : Sigma really has to work on quality control. Releasing an updated version of this lens with smaller diameter and HSM motor would be a plus as well.
10 out of 10 points and recommended
After my bad experience with Sigma 24-70mm F/2.8 EX DG I gave up on chasing a good copy -- I just bought this lens instead and it is fantastic. No cons, just pros! Sharp on both ends, ultra fast and accurate focusing, silent, well balanced with my 40D. For below the 70mm I will get some prime or a cheaper 17-70mm lens and be done with it.reviewed September 11th, 2008 (purchased for $920)