One consequence of technological advances in electronics, including electronic photography, has been a considerable reduction in size of photographic equipment. There are certain factors, however, that limit the further reduction in size of certain devices employing both mechanics and electronics such as digital cameras and the like. One of those limiting factors in the space requirements for the motors that are needed to control the focal length of lenses and the like for electronic cameras. To provide photos that are in focus regardless of the distance between the photographer and the subject, the camera must be capable of sensing the distance to the subject being photographed and be able to adjust the focal length of the lens prior to the picture being taken.
Modern sensing devices are electronic and employ a minimum of space, but there are physical limitations to reducing the size of the mechanics needed to adjust the focal length of a lens. Typically, such cameras have concentric inner and outer tubes, one of which is mounted to the body of the camera and the other of which has a lens across one end thereof. Threadings between the tubes allow adjustment of the focal length by the rotation of the tube with the lens causing axially movement thereof. Where the camera has electronic sensing, it is desirable that miniaturized motors rotate the tube with the lens mounted thereon.
There is a limit to the degree that an electric motor of the type having a rotor, a stator, windings, and brushes can be miniaturized. It would be desirable, therefore, to provide a motor that can be used with small mechanical devices such as electronic cameras, and can be miniaturized beyond the limits of existing electric motors.