Originally Posted by T.Dot_E30
IS allows you to use a slower shutter speed(1-3 stops) in low light, to take better/less blurry shots handheld. It's still always better to use a tri-pod, in which case IS does nothing. It doesn't really have anything to do with the camera 'focusing', but since without it, images are easier to blur due to the camera movement and longer shutter, I can see would you would think that.
If you plan on shotting alot in low light, i'd go for the 2.8 non-IS vs. 4f IS, assuming the prices aren't far off.
I think you hit the spot on. Thanks for making it clear.
terrence330, btw isn't F4L non IS a bit old already for someone like me to buy it now? I think it has been on the market for sometime now... I am not too pushy on buying the latest just to brag about it, If it is something that I appreciate it, I just get it. Just to get your input before I wrap it up.