An actuator for operating a vehicle door includes a spring that is adapted to frictionally connect a wheel gear and an output gear upon actuation of an electric motor. The solid optical body has an axially positioned cavity therethrough which receives a bulb that injects light through a cylindrical wall of the cavity into the optical body. When a phase difference amount between \u03b8i and \u03b8v is small and Ps is close to Fro, the sweeping speed for Fro detection is decreased. The invention further provides a method for dynamically displaying, with or without operator interaction, portions of the contiguous digital image.