How to Pick the Right Binoculars for You
Although most hunters today have scopes on their rifles, you can’t — and shouldn’t glass with a scoped rifle. Not only is it dangerous (remember, there’s a rifle sitting underneath that scope and what you’re seeing could be another person), but there’s simply no need when there are so many good binoculars available at reasonable prices.
But there are a lot of different models of binoculars to choose from, and selecting the right one for you may seem difficult. Here’s what you need to know, including some of the terms used in the optics industry and what they mean for you.
Porro Prism Versus Roof Prism Binoculars
Binoculars come in a wide variety of sizes, magnifying powers and features, but they all utilize either a Porro prism system or a roof prism system, which refers to the type and configuration of the internal prisms used to magnify and transmit light through the binocular to the eye. Porro prisms feature front or objective lenses that are offset from and not in line with the eyepiece or ocular lens. They generally cost less than roof prisms, however, they tend to be bigger, bulkier and heavier.
Roof prism binoculars tend to be more slim and streamlined, with less bulk. Look for roof prisms with phase correction, which is a feature that prevents interference when the path of light crosses over itself while being reflected off of the various surfaces of the internal prism.
What Do the Numbers Mean?
Binocular Coating Options
In order to reduce glare and the amount of available light lost during transmission from the object to your eye, special chemical coatings are applied to the surface(s) of a lens. The quality, number and position of these coatings determine how much light is transmitted. Here are the options available and what they mean:
- Coated — a single layer is applied to at least one lens surface
- Fully-coated — a single layer is applied to all air-to-glass surfaces
- Multi-coated — multiple layers are applied to at least one lens surface
- Fully multi-coated — multiple layers are applied to all air-to-glass surfaces
Figuring Out Diameter of Exit Pupils
As mentioned, the overall brightness, as well as the sharpness and clarity, of a pair of binoculars depends upon a lot of factors, but one way to compare the inherent brightness from one model to another is to compare the diameter of the exit pupils. This refers to the size of the circle of light visible at the eyepiece of a binocular, when pointed at a light source and held about a foot away, but really means how much light is available to the human eye.
The larger the exit pupil, measured in millimeters, the brighter the image, everything else being equal. To determine that number, divide the objective lens diameter by the magnification (an 8×32 model has an exit pupil of 4mm). Full-sized binoculars should have exit pupils at least in the 4-5mm range. Anything larger than that is typically larger than the pupils of an adult human’s eyes, meaning that there is more available light than the eye can use, at the expense of lugging around bigger and heavier lenses. Anything smaller than that and the image is likely not as bright as it could be.
The exception to the 4-5mm exit pupil rule is in regard to compact or pocket-sized binoculars. These models are usually 7x or 8x magnification, with objective lenses usually less than 30mm in diameter. As a result, they tend not be as bright as full-sized models, but this is offset by the convenience of a small, lightweight binocular that you can carry in your pocket or in your glove box. A quality compact binocular that is always with you when you need it is far better than a heavy, bulky model that you always leave back at camp or in your vehicle.