1. A method of capturing a focused image, through an objective, of a slide on a stage, at least one of the objective and the slide being configured to continuously move with respect to the other, said method comprising: triggering a frame grabber device to capture an image of a portion of the slide through the objective as the slide moves laterally with respect to the objective, the objective being disposed at a first focus level with respect to the slide; alternatingly with the step of triggering a frame grabber device, triggering the objective to move to a second focus level with respect to the slide after the image of the portion of the slide has been captured, the objective being movable in discrete steps in a range of focus levels, oscillating back and forth between a minimum focus level and a maximum focus level, the range of focus levels including the first and second focus levels, the frame grabber device being triggered at a frequency as the slide moves laterally with respect to the objective so that multiple images at different focus levels overlap and such that the portion of the slide is common to each of the multiple images, each image having a contrast value; and determining the image having a maximum contrast value within the plurality of overlapping images, the maximum contrast image thereby representing an optimum focus level for the portion of the slide, and thus the focused image.