Today's adventure will take us through the treacherous optics.jungle. Our quest is to find a binocular built just for your needs. Optics are described by two numbers separated by an "x". The first number is the magnification (8x) or how large an object will appear when viewing through a binocular. The last number is the diameter of the objective lens in millimeters (x40mm). The objective lens is the lens nearest the object being viewed. Thus, an 8x40mm binocular will make an object appear eight times closer than the same object viewed with the naked eye and the objective lens is 40mm in diameter.

When choosing an optic, higher magnification is not always better. Generally, the higher the magnification the harder an image will be to hold steady. Also, a compact binocular will be harder to steady than a full size. The amount of light exiting the binocular and entering the eye is determined by the "exit pupil". The exit pupil is calculated by dividing the diameter of the objective lens (40mm) by the magnification (8x). An 8x40mm binocular has an exit pupil of 5mm (40 / 8mm = 5mm). If we were glassing for Kulu during the day, the pupil of a human eye would only open 2.5mm, but will increase to 5mm at dusk. Binoculars with an exit pupil of 5mm or higher maximize the amount of light entering the eye increasing image brightness. An 8x24mm binocular (3mm exit pupil) will perform well under normal lighting conditions where a 7x42mm binocular (6mm exit pupil) provides enough light to see during twilight conditions and into the shadows of the jungle canopy.