Sigma 17-50 autofocus problem

[Dangerous_Dave]

Hi folks.

I have recently bought the Canon EF fitting Sigma 17-50/f2.8 as I read some rave reviews about it. To be fair it is a great, sharp, fast lens. The trouble is it simply will not autofocus on either of my DSLRs (EOS30D and EOS20D), it hunts back and forth before eventually - if at all - giving a confirm beep in an out of focus position.

I've tried all the obvious solutions like turning off custom functions and cleaning the contacts but no dice.

I have done a bit of Googling on the problem and it seems this is by no means a one-off problem with this lens, in fact I'd estimate as many as 1 in 6 reviewers has experienced some problem with the AF. However there seems to be significant disagreement as to the cause, ie is it a faulty lens, or part of a wider compatibility problem with Sigma lenses, due to Canon's reluctance to share autofocus algorithms. Conversely, there seem to be a few people who have had trouble getting older Sigma lenses to work with newer EOS cameras.

I have two EF-fitting AF lenses - Sigma 18-200/f3.5-6.3 and Tokina 11-16/f2.8, and had no problems autofocusing either, although they are both a few years old.

I have posted the lens back for a refund as the supplier is now out of stock, but is it worth trying to pick up another? Is this likely to be a problem with my aging DSLRs, or did I just get a duff lens?

Much obliged for any advice!

 

[modchild]

I've got two Sigma lenses, a 120-400 OS and a 150-500 OS and never have a problem with either of them attaining focus on any of my bodies. It would be a shame if all the newer lenses start having problems with the older bodies as so many people have still got them. It's a shame you couldn't try it on a newer body to make sure.