Abstract: A control apparatus for controlling quickly and correctly, positions of a group of zoom lenses and a group of focus lenses without being subjected to an attitude of a camera. The control apparatus has a group of zoom lenses, a group of focus lenses, actuators for mechanically driving the group of zoom lenses and the group of focus lenses, drive circuits for driving the actuators, and a position detecting devices for detecting each of the present positions of the group of zoom lenses and focus lenses.

Abstract: A magnetic disk drive provided with a computational control circuit for changing the reference level of the A/D converter so that the outputs of A/D conversion are kept constant at all times, which are obtained from integrated output peak values of the sector servo signals on a track having been read in reading a magnetic disk on which sector servo signals are recorded in advance. For the reference level of the A/D converter, values such that the outputs of the A/D conversion on the innermost and outermost tracks become constant are selected in advance, respectively. Thus, that reference level is obtained on the basis of the above values.