I have this lens personally. I bought in 2005 a few months after buying my 350D. Frankly speaking, I was curious to try out a f2.8 lens as i have never use it "out on the shooting field" before. My expectations of picture quality was also increased after looking at so many works. The EFS kit lens just could not sastify.
I used it, actively, in my first 5mths after buying my DSLR. The AF i would say would be noisy nevertheless, but not to a point that when used in a very quiet setting it can be heard distinctively. I was at a quiet indoor walkway of a building where some cornices caught my eye. I slapped on my Sigma and took some pictures of it. The AF noise was not distracting enough to alert a person in front of me just a few meters away.
Ading on to the AF issue, i was very happy with the f2.8 thru out feature. It is very very workable in low light conditions. It never hunt in low light for me at least. However, i seldom shoot wide open unless forced by very low light conditions. I usually stop down, up iso, on flash, calibrate flash to prevent white washing and go for the shot. In most light conditions, the AF lock on almost instantly. USe it with a 30D with a highly sensitive centre AF point, i think its a very good low budget combination for amateur-hobbyist photogrpahers as compared to buying an L glass.
Unfortunately, the f2.8 turn out to be a feature which i can't master. The focus plane is so shallow (which is viewable in the viewfinder) that any movement will shift the focus point significantly(especially at the tele end). As a result i keep throwing off my intended point of focus in most of my shots.
The colour reproduction is great bearing in mind that its a third party lens. All the colors were close to accurate. Some of my friends said before that Sigma is warm in colour reproduction but this can be counteracted easily using Adobe or probably even shooting in raw and using a RAW work flow. Picture quality is great too, i own a L and i in my opinion sigma pictures can be comparable to Canon L lens.
As for pic quality and lens quality, i guess there is very little to worry about. Mid zooms have been there for quite sometime now as it was meant mostly for FFs film SLR/DSLR. The technology on this focal range has come to such a mature stage that there is very little you can compare between Canon, Sigma and Tamron. Just make sure u get the latest iteration of the lens(there are versions without the Macro word) and also the one u are buying is by far the freshest batch out from the factory.
Sigma is quite reputable in Japan too. Most of its lens all bear the words: "Made in Japan". Sigma have also their own DSLRs body which to a certain extent follow the EOS product design. Only thing it does not perform as well as Canon's. I have a teacher who owns a film EOS 3 who uses Sigma lens too.
I m currently selling this lens in BnS as i do not use it in my photography. Also, the mid zoom for me will be to use a prime within this range.
Well you work out your choices, and see what best suits you and your budget.
