Originally Posted by
Bori300
oh ok i understand now. so its how long the shutter stays open for the amount of exposure desired.
so say like for a rolling shot with panning it will help get that blurred background affect but keeping the image of the car sharp.
If you're rolling already, you don't need to pan.
Match the shooting-from car's speed to that of the car you're shooting (30MPH, whatever), focus, shoot. Adjust shutter speed as necessary to get blurred background and blurred wheels as you see fit. Try anything from 1/60 to 1/300 and see what you like. Remember, too, that if you speed up or slow down (the cars), you may need to readjust shutter speed.