It's 5.6. I just used the "sports" mode saturday due to the light being so harsh, and I was swinging back and forth at 2 different groups of surfers. I've had 3 Sigma lenses and all of them have taken great photos. Only have 1 Canon L in 70-200 for the time being. Wanting a 600mm real bad.

Very good edge to edge sharpness and no vignette for an offbrand lens. You got a good buy there. I'm using a Nikon 80-300mm ED lens. What's the f/stop for your lens at 400mm?

Some excellent action shots on your http://pages.suddenlink.net/jgphoto/index.htm website. What size lens are you using for the surfing images, 500mm? And it's a Canon, right?