- Eye relief —The distance between your eye and ocular/front lens. Longer eye relief is important for eye glass wearers. Exit pupil—a larger exit pupil makes it easier to put the eye anywhere in the viewing cone to avoid a darkened view.
- Magnification — The magnification of the object you’re viewing and how many times closer it appears. Eg. 7 x 35 – object appears 7 times closer. Field of view—Describes how many feet (i.e. 350 ft.) in width can be seen at 1000 yards.
- Objective Lens — In the example, 7x35, the second number represents the diameter of the objective lens. The larger the number the brighter and sharper the image.
- Anti-reflective lens coatings — Special lens coatings that reduce light reflected away at each optical surface.
- Waterproof — Prevent internal fogging and moisture condensation when conditions are wet. Not all binoculars are waterproof.
Binoculars: An ideal use
How far away are the objects that you normally want to view? Do you need to track moving objects or are you on a moving surface? Do you wear glasses when using your binoculars? Your answers to these questions will help you determine the right binoculars for you.
Once you know your viewing needs, you can narrow down the choices of binoculars accordingly.
Birding: To get a brighter, close up view of birds, you may want to consider a larger magnification and objective lens diameter. Ensure there is adequate eye relief if you like to track birds in flight.
Water Sports: To ensure you get a stable image, lower magnification binoculars will be less susceptible to shaking while you are on a boat or moving object. Choose water-tight binoculars if there’s a chance they’ll be used near water or in rainy weather.
Outdoors/Travelling: A wider field of view is easier to track objects, which may be an important consideration when hiking, hunting or travelling outdoors.
Spectator Sports: Binoculars that feature a wide field of view and 7x to 10x magnification are handy for fast-moving sports. Zoom-type binoculars are convenient to enable quick and easy changes to magnification to suit the viewing situation.
Astronomy/Stargazing: For stargazing, select a larger objective diameter (35-40) and exit pupil to increase the amount of light captured, and help see the faintest star.
Nikon Sport Optics Resource Guide (pdf)