Focusing of CF binoculars
Rotating the central focusing ring engages the internal shafts. Then, the tubes that fix internal lenses (concave lens) move so that the binoculars focus. Because objective lens and eyepiece lens are fixed, binoculars can have a highly airtight structure. This is recommended for CF (Central Focusing) waterproof binoculars.
Focusing of IF binoculars
Rotating diopter adjustment rings that are located on both left and right eyepieces, moves the entire eyepiece lens unit in order to focus.