I used to shoot with a Canon 28-70 2.8 L lens, and it was on my camera a good 70-80 percent of the time (the 70-200 2.8 would've been on it the other 20-30 percent).
Unfortunately, the old lens was dropped, and the autofocus stopped responding, and the mount was a little warped (the 20D it was on had nothing but a mere scratch on the pop-up flash).
So I needed a replacement.
For 200 dollars, this Sigma lens gives practically the same results that I found I got with my 1400 dollar Canon lens.
That fact alone is remarkable.
With that said, I miss the ergonomics and small subtleties of the larger and heavier Canon lens;
- Like the Canon it replaced, the Sigma does not focus or zoom internally. However, the Canon was a smarter design in that its' lens hood attached on threads located on the outer lens barrel, not the end of the end element. This lens hood protected the extended part of the lens, which when used on a rough and tumble daily basis was definitely a plus.
- The ultrasonic motor. Every time that AF-ON button is pressed, you (and moreso your subject) notice a distinct insect-like buzz. I use the 28-70 for weddings, and I purchased the Sigma to replaced the broken Canon. I dread autofocussing with this lens in a tiny country church during what should be a solemn sacred ceremony... chances are, I'll be manually focussing during such an event.
With those two points aside, the main thing this comes down to is price. 200 flippin' dollars CDN is what I paid for this in a clearance sale from a Sigma distributor. That's 550 dollars less than what I paid for my old Canon 28-70 used, which was half of the 1499.99 retail it's successor goes for now. If you photograph as a business, this lens will pay for itself in a job or two.
I highly recommend this lens as an alternative to the much more expensive (but better) Canon equivalent.