Abstract: A focusing apparatus is provided for facilitating the adjustment of the focus for a fixed optics, folded collimating lens in an X-ray imaging system. An idler member is gear driven by an adjustment knob, and is threaded to receive a mating threaded portion of the collimating lens. The collimating lens is constrained from rotating by set screws on horizontal arms which bear on a stationary bushing. Rotation of the adjustment knob thereby causes rotation of the idler member while the collimating lens is restrained from rotating. This results in straight vertical movement of the collimating lens, up or down, until optimum focus is achieved. The set screws also provide for fine rotational alignment of the collimating lens with an image head.