Abstract: The apparatus features a rotating collar and a static collar, in which one collar has an adjustment lever. The rotating collar is attached to a rotating portion of a focus knob for a device, which in one example is a night vision device. The static collar is attached to a non-rotating portion of the device immediately adjacent to the focus knob. The movement of the rotating collar and the focus knob that the rotating collar is attached to is constrained by mechanical interference between a static stop, the adjustment lever, and an adjustable stop.