A good thing to know...
You should hand-hold a lens only when your shutter speed is at least equal to the focal length in millimeters. That is, a 100 mm lens should not be hand-held below 1/100th of a second; a 500 mm lens should not be hand-held below 1/500th of a second, and so on.
However, to assure razor-sharp images it is recommended that you set your shutter speed even faster to double the focal-length of the lens. That is, a 50 mm lens should not be hand-held below 1/100th of a second; a 100 mm lens should not be hand-held below 1/200th of a second.
It's not rocket science but it is photographic technology. Use this info at your leisure for super-crisp pics!