The present invention is a spotlight with adjustable focus that has a focus fixing mechanism to prevent inadvertent changes to the focus of the light, while still allowing user-friendly intentional adjustment of the focus. The mounting collar of the reflector assembly rotates on helical threads on the neck of the lamp assembly so that the focus of the light may be adjusted. The focus is fixed in position by a plurality of ridges and valleys on the lamp assembly that mate with corresponding ridges and valleys in the collar of the reflector assembly. The collar of the reflector assembly is sufficiently flexible or expandable so that the focus of the lamp may be intentionally changed by applying sufficient rotational force to the reflector assembly. The collar is sufficiently rigid that the reflector assembly will not rotate as a result of incidental vibrations or movement.