An annular array ultrasonic transducer is provided which comprises a plurality of concentric rings of piezoelectric material having widths chosen for operation at different depths of focus. The total aperture of the transducer is divided into a plurality of contiguous focal depths. In the near field only the inner element or elements are activated, and rings of increasing radius are added as the depth of focus is increased. The widths of the rings are chosen to keep phase errors across each ring within acceptable limits over the depth of field for which they are energized. The transition depths at which the aperture is changed are chosen to allow rings of manufacturable widths to be employed while maintaining aperture transitions which prevent banding in the ultrasonic image.