A diagnostic instrument includes an illumination system for providing illuminating light and an imaging system for directing the illuminating light to a target and for transmitting light reflected from the target to a viewing location. The imaging system includes an electrically controllable variable focus liquid lens assembly for focusing the light reflected from the target at the viewing location. The liquid lens assembly includes at least one liquid lens including a housing filled with a first liquid, and a drop of a second liquid being in contact with the first liquid in a predetermined form. The lens further includes a first electrode insulated from the second liquid and a second electrode in electrical contact with the first liquid. A variable voltage control selectively applies a voltage to the first and second electrodes to vary the focus of the lens. An electronic imager is provided to capture the reflected target image.