Originally posted by kenyee I've never shot my Sigma 10-20 wide open at f/4. It's just not sharp enough wide open, even in the center. For night shots, it's always f/8-13 on a tripod and nearly always at 10mm. f/2.8 to f/4 is only one stop...f/3.5 to f/4 is even less :-P
Of course, the older Sigma is only f/5.6 at 20mm, so that's 1 1/3 stops. Anyway, for some applications (street-shooting, photojournalism...), its not necessarily about optimal sharpness or limiting depth-of-field, it's about getting the shot with reasonable shutter speed to stop motion & camera shake...and a tripod won't necessarily do it. Even a mild performance improvement combined with a faster max aperture will convince many people to drop another $200 on this lens instead of the older 10-20/4-5.6. And do you doubt that this lens will likely outperform the older one at smaller apertures as well (time will tell, but I won't be surprised if it does).
Originally posted by kenyee I'm pretty sure I'm a different market than what Sigma is targetting w/ the 10-20 HSM, unless they've dramatically improved the edge sharpness (my main complaint about the 10-20) and it'll partially work on FF systems like the Tokina can at 14mm.
I'm not going to talk about this being dead in the water vs. the Tokina unless it appears in our mount of choice, most likely in Pentax DA* trim. Not a peep about it yet, so it may never happen--which would be a real shame. Furthermore, some might choose the 10-20 range over the more limited 11-16 range anyway...and all this is without even considering price differences which is unknown at this time.
Having choices is good.