When compact mirror telephoto lenses are used with light tri-pods, a major source of image blur is shutter-induced camera vibration. The impulsive torque about the center of mass of the camera-lens system, produced by the sudden shutter motion, generates an angular velocity that sweeps the optical axis across the object during the exposure. The antivibration mount, by means of an adjustable counterweight, relocates the system's center of mass to coincide with the shutter plane, thus reducing the impulsive torque to zero. Because the optical axis now maintains a fixed direction during the exposure, a sharp image is registered on the film. Tests with an 800 mm lens demonstrate that this simple mount permits very light tripods to be used with very long focal lengths.