Disclosed is a zoom lens system which uses a diffractive optical element such that high optical performance can be obtained over the overall power variation range. The control system uses the computed motor model to produce a closed-loop control design that achieves a particular resolution. Moreover, the system may modify the video image so that a product of the intensity setting and a transmittance associated with the modified video image approximately equals a product of a previous intensity setting and a transmittance associated with the video image. It is preferable that in a first mode with the first and second pair of speakers in an unstacked configuration, the signals do not pass through the arrangement of electronic components prior to output. A further feature of the invention allows a variable resolution image to be converted to a fixed resolution image.