Light Transmission and Coatings
Light is lost as it passes through binocular optics. Inexpensive pairs might pass as little as 50 percent of the light to the viewer, while quality glasses will provide light transmission in the 80 percent to mid-90 percent range. To reduce reflection and increase light transmission, lenses are coated, typically with a magnesium fluoride, and higher-end manufacturers might add proprietary scratchresistant compounds. "Fully coated" lenses might sound good but are actually less desirable and usually found on lower-end products. Binoculars labeled "multicoated" will gather more light, and the best products are "fully multicoated" — sometimes abbreviated as FMC.
Field of View**
This is the area you'll see through the binoculars, expressed either in degrees or in the width of the area seen at a thousand-yard range. A field of view of seven degrees (or about 375 feet) is usually considered optimum for general marine use.