Selecting the appropriate Binoculars for the purpose:
Marine rated quality binoculars are an essential tool for any mariner. All binoculars magnify your view and allow you to distinguish markers on the horizon, but not all glasses are equal. Some lack clarity and durability, leaving you swearing oaths to get better binos as soon as you reach shore. (This phenomenon typically occurs around dusk while straining to find that safe water marker toward home.) In low light conditions, good binoculars earn their keep through exceptional clarity and detail. Knowing how to choose a pair with improved light gathering capability and quality optics will help in deciding what works best for you.
When selecting binoculars, it helps to understand some simple basics. Binoculars are rated by two values, Magnification x Objective Diameter, for example 10 x 35 or 7 x 50. The first value, magnification, describes the apparent closeness of distant objects. The higher the magnification, the closer any distant object will appear. The drawbacks to higher powered binoculars are narrow periphery and difficulty maintaining a stable image. Most standard binoculars use 7x magnification as a good compromise between stability and periphery view. The second number ( x 50) is an indicator of the light gathering capability. This is determined by the diameter of the big lens, measured in millimeters. For on the water use, 7 x 50 is the standard. This formula yields enough magnification, a fair range of view and remains steady enough on a rocking boat. On the opposite, an amateur astronomer observing distant objects from terra firma, is better suited selecting 10 x 50 powered binoculars. The last measurement to consider is field of view. Most binoculars include the field of view rating printed on the glasses. Field of view measures the angle or width across the horizon observed at 1000 yards. A larger field of view is very useful when searching the horizon or trying to spot moving wildlife. A large field of view is practical for bird counting or whale watching.
Beyond the numbers, most binoculars have some sort of prism system to create a natural looking image. Good prisms should not strain the eyes or create darkening around the edges of vision. Some are better than others at collecting light and are reflective of that in their price. Because the prisms rely on precise alignment, it is best to shield them from harsh impacts, as hard knocks can quickly misalign and distort them. Most also use coating on lenses to increase sharpness, brightness and contrast. O-ring seals at the lenses hold out moisture and nitrogen allows light to travel best without reflection off internal moisture. It also prevents fog. Offshore marine binoculars typically include extras such as range finding and built in compasses. Range finding is useful for ball parking distances while built-in compasses can quickly give bearings. These features are particularly useful when distinguishing navigational marks on moonlit nights or near dawn and dusk. Lastly, eye relief, or how far the eye is away from the eyepiece, helps eliminate the circle effect. Some eyepieces are adjustable by rotating or others have a soft rubber style than can be folded back when looking through sunglasses. Should all these features still leave you in the dark, perhaps night vision glasses are in order!