Binocular specifications indicate the capabilities of the models available and their suitability for different users, so identifying users' needs is the first step in interpreting binocular specifications. Keep factors such as desired focus distance and typical usage conditions in mind to find the ideal pair. Before buying binoculars from a seller on eBay or elsewhere, learn how to assess the models available. Consider aspects such as magnification power and objective lens diameter, exit pupil size, field of view, lens coatings, and additional features to make an informed buying decision.
Magnification Power and Objective Lens Diameter
Manufacturers indicate binocular magnification power using two numbers. The first reflects the magnification power and the second the diameter of the front or objective lenses. A pair of 8 by 30 binoculars has a magnification power of eight, so objects in focus appear eight times closer than they do to the unassisted eye. In this example, the objective lens has a 30mm diameter. The size of the objective lens determines how much light enters the binoculars, and the amount of light determines the brightness of the view. More light is especially useful in low lighting conditions, but binoculars with large objective lenses are bulkier and heavier than those with small objective lenses are. Although higher magnification powers may seem better, those higher than 10 intensify the movements of the users' hands, which causes stability issues. In addition, higher magnification decreases field of view and exit pupil size. Zoom binoculars offer adjustable magnification, which allows a user to use lower settings for searching for objects and higher settings to focus on them.
Exit Pupil Size
The exit pupil is the opening that allows light to leave the barrel of each side of the binoculars and reach the pupils of the user's eyes. To see the exit pupil, look at the eyepiece of one barrel from about 30cm away while the objective lenses point towards bright light. Calculate exit pupil size by dividing the diameter of the objective lens by the magnification factor. For 8 by 30 binoculars, the size of the exit pupil is 3.75mm. A wider exit pupil allows more light to pass through the binoculars, which improves images in low lighting conditions. In bright light, the pupil of the human eye contracts to around 2mm, so exit pupil size becomes less significant. However, the pupil tends to expand to up to 7mm in poor light. Users who often use binoculars at dusk, dawn, or in heavy bush should look for binoculars with exit pupil diameters of 4mm or more.
Field of View
The real field of view indicates the width of the area a user can see at 1,000 metres without moving the binoculars, measured from the centre point of the objective lens. A wide field of view allows the user to search for and identify objects such as wildlife and birds. As magnification increases, field of view typically narrows. The apparent field of view is the angle of the magnified field a user sees when looking through the binocular lenses. A larger apparent field of view provides a wider field of view even at high magnification.
Anti-reflective Lens Coatings
Anti-reflective lens coatings prevent light loss that diminishes brightness. Coated lenses are the most common and least expensive, and feature coatings on some of the air-to-glass surfaces. Devices with fully coated lenses have anti-reflective coatings on all air-to-glass surfaces. Multi-coated lenses have multi-layer coatings on some surfaces, and fully multi-coated lenses have multi-layer coatings on all surfaces. Fully multi-coated lenses offer the greatest protection against loss of light.
Additional Binocular Features and Specifications
The way manufacturers construct and designs binoculars determines their comfort and durability. Eye relief, interpupillary distance, and waterproofing varies between brands and models.
The ideal eye relief and inter-pupillary distance differ between users. Buyers should test different configurations and specifications to determine what is comfortable for them. Waterproof binoculars are ideal for damp conditions and tend to be more durable than regular models are.
How to Buy Binoculars on eBay
Sellers found on eBay offer a wide selection of compact, standard, and high-powered binoculars. When searching for binoculars, use a detailed phrase such as 'Nikon binoculars' or 'Zeiss binoculars' to narrow your search results. Alternatively, choose the most suitable category and item features from those available. Look for local sellers who allow collection if you want to save on postage and packaging fees and receive your new binoculars as quickly as possible. Focus on binoculars with specifications suited to your viewing habits and needs while keeping cost, weight, and size in mind.