There are two main lenses, or groups of lenses, inside a pair of binoculars. The front lens (the one farthest from your eyes) is the objective. This collects light from what you are looking at and focuses it into a small, bright image within the darkened tube. The eyepiece magnifies the objective’s virtual image and turns it right side up. There has to be a minimum distance between these two, and binoculars use internal prisms to achieve that distance in a housing of small size.