probably f/3.5-4.5. Bummer for me! I eagerly awaited the Sigma
50-150 f/2.8 only to receive a copy that has a stuck apeture and is
SUPER soft at 150mm any closer than 20 ft.
I'm on my second copy of the 50-150 2.8 and it's soft at 150 only
because it's front focusing. If you look real good, you'll find
something tack sharp in focus. It's a shame Sigma couldn't get
this working right. I'm debating if I want to keep it or not.
It's better at 135mm but the difference in the zoom ring makes
shootin 135 very difficult.