Central focusing binoculars have three moveable adjustment.
1. The first is called the interpupillary adjustment which means adjusting the barrels so the binoculars fit to the users particular eyespan. Begin by moving the eyepieces closer together or farther apart until they are comfortably in front of your eyes.
2. The second adjustment takes place at the center wheel, the focusing knob that moves both eyepieces at the same time. However since there is often a difference between the user’s two eyes a third adjustment is available to correct that difference.