Sigma 15-30mm f/3.5-4.5 EX DG IF question

The Sigma 15-30mm f/3.5-4.5 EX DG IF was first available as a "EX DG" without the mechanism to keep the outer focus ring from rotating. Now it's a DF and has it. At least as far as I can tell, it's not easy to find information on the old version.

if that's true, is there any other difference? I'd really like one of those and the old version often goes quite a bit cheaper.

I have the Sigma 15-30mm 1:3.5-4.5 EX DG IF lens. I haven't used the DF version. The DG is a nice lens to use and feels light for its size and is quite sharp. There is some barrel distortion at the wide end that shows up on full-frame but isn't bad with a crop camera. The 12-24 EX is better for distortions but has other drawbacks.

The focus ring can be slid back and forth.

If you don't want the focus ring to turn during autofocus, then push the focus ring toward the front of the lens to decouple it. Pull it back again when using manual focus.

Thanks for the info. Sounds like a good lens for me.