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Binoculars 101: How to Choose Binoculars

By Paul Kendall @ Vortex Optics | Posted 5/29/2020

There’s no shortage of options for binoculars, with solutions available for hunting, birding, or any other long-range observation applications. With this plethora of options, it can be hard to determine where to start. So, today, we’re going to go through the basics of binocular construction and look at some of the styles available today to give you an idea of what suits your needs.

Binocular Anatomy and Design


To better determine which set of binoculars is right for you, it’s important to familiarize yourself with the parts of a binocular. They are:

  • Ocular lens - The lens closest to the user’s eye.
  • Objective lens - The lens furthest from the user’s eye.
  • Center Focusing wheel - the dial on the bridge which adjusts the binocular focus. Most binoculars also feature a right-eye diopter adjustment, which fine-tunes the right eye specifically. This allows for independent focusing of each eye.
  • Eye Cups - The pieces surrounding the ocular lens. The closer you can get your eyes to the ocular lens, the greater your field of view will be. Most binoculars today feature adjustable eyecups, which work particularly well for users who wear glasses.

Magnification


On the center focus wheel of most binoculars, you’ll find a set of numbers. These numbers are used to identify magnification capabilities and the lens diameter of a given set of binoculars. For example, you may find a “10x42” set of binoculars. The “10” indicates that the object is magnified to 10x its original size. The “42” expresses the size of the objective lens -- that’s the outward-facing lens. As a rule of thumb, lens size works similar to a window. The larger the lens, the more light is allowed through the glass.

Another common term is “exit pupil”. The exit pupil is the small beam of light that can be found on the back end of the binoculars. The larger the exit pupil, the more light will be allowed through to hit the user’s pupil, creating a brighter image.

Consider this: in brighter conditions, the human pupil contracts to limit the amount of light let in, and in darker conditions, it expands to bring more light in. So, in brighter conditions, a smaller binocular exit pupil is often perfectly adequate. In darker conditions, you’ll want to use a larger set of binoculars with a larger exit pupil.

To determine the exit pupil, simply divide the objective lens size by the magnification number. So, in the previous example of a 10x42 set of binoculars, you would find a 4.2 mm exit pupil. This is suitable for lower light conditions, whereas more compact binoculars will feature a 2-2.5mm exit pupil. For extreme low light conditions, you can find 10x50 binoculars that feature a 5 mm exit pupil.

Roof Prism vs Porro Prism


There are two main binocular designs available. They are roof prism binoculars and Porro prism binoculars.

  • Porro prisms - These are the slightly more traditional style, which are characterized by the objective lenses being offset from the ocular lenses. They’re typically a bit bulkier, while not as durable as roof-prism models. However, they are often less expensive and feature fantastic image clarity and resolution.
  • Roof prisms - These are typically more popular, and feature a straight line from the objective lenses to the ocular lenses. Recent developments in technology have made roof prism binoculars an effective, rugged tool for both hunting and birdwatching.

Waterproofing


We should touch on the topic of waterproofing binoculars. For field use, it’s important to purchase waterproof binoculars. Waterproofing is accomplished by using argon or nitrogen gasses to purge the binoculars.

Anti-Reflective Coating


Binocular manufacturers attempt to eliminate glare and reflection as much as possible, so the maximum amount of light is able to enter the binoculars themselves. To accomplish this, they use different anti-reflective coatings. When shopping for binoculars, try to find fully multi-coated and/or phase-corrected models.

In higher-end binoculars, you can find options like HD, IDI, or XD glass. These types of specialty glasses will give you a truer image with less chromatic aberration. If you’re looking for high-performance binoculars, we suggest HD or XD glass.

Tripod Mounting


High powered binoculars are going to be particularly heavy and difficult to hold for long durations. So, many of these models will come threaded, which means they can be mounted on a tripod. With tripod mounted binoculars, users can achieve a greater field of view, allowing themselves to see much greater distances than with smaller models.