Summary: The Tasco OffShore series are waterproofed, rubberized binoculars for a marine environment. The model below (OS 21) is the same optics WITHOUT the compass. The model above (the OS 54) has more and better coatings on the lenses. The OS 36 is the middle model and the biggest seller. All these binoculars are well suited to a watchstander on a boat. They are FIXED FOCUS (although there are diopter adjustments on both eyepieces). Focus is meant to be set on the horizon.