Photography Tips and Tricks - 41 (Shutter Speed Rule for Focal Length)
There is a rule for shutter speed and focal length. This works for static or slow-moving objects. The rule is to have a shutter speed equal to 1/focal length. So, a 200 mm focal length should be 1/200 or faster. This is to compensate for the camera shake. If you have a fast-moving subject try doubling or tripling the shutter speed.