Carson Optical Binoculars - Manual (Page 5)

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.