A relay lens assembly (100) for use with a microscope (1400), telescope or binocular (1500), comprises a lens element (300) that is responsive to commands, conveyed from a control unit (400), via a conduit (410) between the control unit and the lens element. A computing device (810) controls operation of the lens assembly and a digital camera (805) that has an image sensor (125). The control unit causes the lens assembly to assume any of a plurality of predetermined focal lengths so that different depths of an object being imaged can be rendered in-focus on the sensor. A series of images can be taken at predetermined, computer-controlled focal depths. These images can be processed in order to create a photomontage that is in focus at a plurality of predetermined depths in a process commonly called focus-stacking. The addition of a plurality of data input and analysis units (1105) and a combiner (1115) makes rapid processing of individual images possible for photomontage at video rates.