A lens cover device for a camera lens, particularly suited for use with a telephoto lens and hood assembly, comprises a disk-like body member having a plurality of retention members. The control unit compares each actual target speed signal to an associated wheel speed signal to obtain a wheel speed error signal for each wheel and converts each wheel speed error signal to a clutch control signal, wherein each differential clutch actuator is responsive to an associated clutch control signal. Protective tube reliably prevents burning off of the heating element and thus a deterioration of the properties of the fiber.