An optical device for viewing an image is provided. The optical device includes two optical channels, each optical channel including an image detector assembly and a complimentary objective lens assembly spaced by a respective distance from the image detector assembly. A focus mechanism is either directly or indirectly coupled to both Image detector assemblies. The focus mechanism includes two threaded segments having an unequal thread pitch. Each image detector assembly Includes a mating threaded segment that is threadedly coupled to a respective threaded segment of the focus mechanism such that rotation of the focus mechanism causes translation of both image detector assemblies at unequal rates by virtue of the unequal thread pitch of the threaded segments of the focus mechanism.