Porro Prism Systems: the objective lens is offset from the eyepiece. Light is redirected through the binocular internally. The result is a shorter, stockier shaped binocular. In general, porro prism binoculars offer a wider field of view. Most zoom binoculars use the porro prism system for this reason.
Eye Adjustments
How to adjust for distance between your eyes:
The distance between the eyes, called “interpupillary distance,” varies from person to person. To achieve perfect alignment of lens to eye, follow these simple steps:
1.Hold your binoculars in the normal viewing position
2.Grasp each barrel firmly. Move the barrels closer together or farther apart until you see a single circular field. Always reset your binoculars to this position before using.