Binoculars Basics By Nikon
Performance factors
Nikon offers an extensive lineup of binoculars — including several of the world ́s most popular series — for a diverse range of applications. Each model features various technical specifications that can help you in making the right selection. Magnification is usually considered most important, but field of view, brightness, ease of handling (weight, feel, ergonomics), suitability for eyeglass wearers and overall construction should also be taken into account.
Magnification, represented by a numerical value, is the relationship between a subject ́s actual proportions and its magnified size. With 7x magnification, for example, a subject 700 metres distant appears as it would when viewed from 100 metres with the naked eye. As a rule, magnifications of 6x to 10x are recommended for handheld outdoor use. With magnifications of 12x or greater, any shaking by hand movement is more likely to create an unstable image and uncomfortable viewing.
Field of view
All binoculars use number codes to designate various specifications. In “8x40 8.8°”, for example, “8.8°” represents the real field of view, which is the angle of the viewing field measured from the central point of the objective lens. The apparent field of view, on the other hand, conveys how wide that field of view appears to the naked eye. The real field of view at 1,000 metres listed in the specifications is the width of the visible area at a distance of 1,000 metres.
Objective lens diameter
The objective lens diameter, combined with the quality of lens and prism coatings, determines the amount of light gathered to form an image. If you are regularly observing in poor light conditions, such as early dawn or dusk, or in forested areas, you may need a larger objective lens. But large-diameter objective lenses make binoculars heavier, so 50mm is the general limit for handheld use.
Exit pupil
The exit pupil is the image formed by the eyepiece lenses. The diameter of the exit pupil (in mm) is the effective aperture divided by the magnification. The diameter of the human eye pupil varies from 2-3mm in daylight to 7mm in the dark. An exit pupil of 7mm gives maximum light to the dilated eye and is ideal for use in the twilight and at night.
The relative brightness value is obtained by squaring the diameter of the exit pupil. The greater the relative brightness, the brighter the image will be. However, this value does not correspond exactly to increases in brightness viewed with the naked eye because light coming through the binoculars is 100% effective only if the exit pupil is the same diameter as the pupil of the eye.
Check the letters in the name of any Nikon binoculars — they convey helpful information about each model.
D: Roof (Dach) prism WP: Waterproof
CF: Central focusing IF: Individual focusing HP: High eyepoint