It's important to understand the basics of binoculars before choosing
When it comes to picking the best binoculars, the range of choices can be staggering. Experts say you should first consider how often you plan to use your binoculars, what you intend to use them for and how much you want to spend. For example, if all you need is a pair of binoculars for the occasional ball game or vacation, you can find a quality model for less than $300. But if you are a dedicated bird-watcher or hunter, you'll want to spend upwards of $2,000 for a high-powered, rugged binocular. Once your budget is decided, you'll need to know a little about the different binocular parts and specifications in order to choose the pair best suited to your needs. In this report we break down the basics of binoculars and then identify how they are best suited for your intended use.
Magnification may be the most important factor
The magnification power -- the zooming ability of a pair of binoculars -- is often the distinguishing factor between models. The magnification is determined as how close the binoculars make the object you are viewing appear compared to seeing it unaided; for example, 8x means whatever you are viewing will appear eight times as close. The magnification is always the first number listed on a binocular label. Models with variable zoom are labeled with their range, such as 7-21x50, which means 7x to 21x magnification. Experts prefer fixed-zoom models, since the further you zoom the smaller the exit-pupil diameter becomes and the less light enters the binoculars, thus reducing image quality. The most common binoculars, good for everyday use, are between 7x and 10x.
Objective-lens and exit-pupil diameter
The second number on a binocular label is the size (diameter) of the objective lens, the lens furthest from your eyes. The larger the objective lens (measured in millimeters), the more light can enter; and the more light that gets through the brighter and clearer the image appears. The objective lens is sometimes called the aperture or front end.
The size of the objective lens also determines the exit-pupil diameter, which is determined by dividing the objective lens size by the magnification. For example, 10x42 (a common size) means an objective lens of 42 mm and an exit-pupil diameter of 4.2 mm. Marc Spiwak from BHPhotoVideo.com explains why this is important: "The pupil of a human eye ranges from about 1mm in bright conditions to about 7mm in the dark. If your binoculars' exit pupil diameter is smaller than the pupil of your eye, it's going to seem like you're looking through a peep hole." The exit pupil typically ranges from about 2 mm to 7 mm.
Field of view and minimum focus distance
As the magnification of binoculars increases, it becomes harder to find the subject you wish to focus on. In other words, the field of view decreases.
The field of view refers to the width of the user's view when looking through the binoculars, and is affected by a few factors -- most significantly the objective lens and magnification power. When all other factors remain constant, a larger-diameter objective lens means a larger viewing area, a brighter image and (naturally) a heavier pair of binoculars.
Field of view is usually measured in feet; "For example, say you're looking at a ship that's 1,000 yards away; binoculars with a 330-foot field of view would show you 330 feet of the ship, measured horizontally," explains Spiwak. (Field of view is sometimes called angle of view, and is measured in degrees -- how much of the 360 degrees around your head you can see through the binoculars.)
Additionally, greater magnification means a larger minimum-focus (or close-focus) distance, which is the minimum distance from the object the binoculars must be in order to focus.
Adjustable eye relief is important for those wearing glasses
An important specification to keep in mind if you are new to binoculars is eye relief, the distance between your eyes and the binoculars. The eyecups on binoculars are supposed to set the ocular lens at the optimal distance from your eye, but if you wear glasses, they prove ineffective.
Reviews recommend a minimum of 14 to 16 mm eye relief for people who wear glasses, but it is important to try your potential binoculars in order to test the eye-relief adjustability. If the eye relief is too short while wearing your glasses, you will experience tunnel vision -- a decrease in field of view; if too large, you will need to hold the binoculars some distance from your eyes. This can get tiring and cause an unsteady image. The adverse is true as well. Reviewing binoculars at BetterViewDesired.com, Wayne Mones explains: "The closer your eye has to be to the eyepiece the more fatigue the glass will cause. Having your eye close to anything continually triggers the blink reflex." Usually, you can adjust or flip the rubber eyecups to achieve optimal eye-relief distance when using glasses. Note: Testers in comparative reviews evaluate eye friendliness by actual usage, often rating a binocular higher or lower than the eye-relief specification would predict.
Understanding binocular prisms and shapes
In a general sense, there are two main types of binoculars: roof prism and porro prism, referring to the setup of the prism, which are used to turn your view right-side-up. Roof-prism binoculars look like the letter H, weigh less and are more compact and comfortable to hold. These H-shaped binoculars are usually dust-proof, waterproof and fog-proof. Fog-proofing makes the binoculars usable even in very cold or humid weather, when most would fog internally.
The glass elements in porro-prism models (shaped like a W) are offset, creating a bulkier, heavier unit. In the past they were considered optically superior, with a greater depth of field and a wider field of view. That is no longer the case. Expert sources we consulted say that, thanks to today's technology, there is little optical difference between the two types of binoculars. Porro-prism binoculars are cheaper to make, so they may be ideal when shopping on a budget, but they are often not waterproof or fog-proof.
Binocular types and uses: compact versus full-size
Since a larger lens lets in more light, binoculars with larger objective lenses are theoretically better in low light, but they are also larger and heavier. Compact binoculars, which are handy for sporting events, concerts, hiking or general use, have objective lenses of 30 mm or smaller. They're lightweight and convenient, but usually provide less detail and brightness. Mid-size binoculars, with objective lenses of 32 mm to 35 mm, are often more comfortable to hold than full-size binoculars, but offer a dimmer view.
Full-size binoculars, with objective lenses from 36 mm to 50 mm, usually offer the brightest image and are best for birding and hunting. You may have seen some giant binoculars you couldn't imagine carrying on any hiking trip. These are often used for stargazing (though 10x50 is also a good size for astronomy) and are best used with a tripod.
For general use, experts recommend 8x42 or 10x42 binoculars, especially if you don't want to pay more than $500. You can see more detail with 10x magnification, but unfortunately, any flaws in the optics or design of the binoculars are also magnified. For bird-watchers, experts recommend binoculars with 8x (or less) magnification because their wide field of view makes it easier to find viewing targets and they're not as heavy as 10x binoculars. The wider field of view means you'll see more of a landscape or sports field without shifting your gaze.
While good budget models are available, binoculars can be quite an investment. As a result, comparative binocular reviews are extremely important for determining which binoculars are worth their price tag. We found a number of comprehensive and thorough binocular reviews in outdoor magazines. Outdoor Life magazine, in particular, has the best and most recent testing. Editors enlist the help of five expert testers to evaluate 23 pairs of binoculars. Not only are the binoculars ranked for optical quality, they also receive an overall rating and individual scores for image quality, value and design. The best binoculars receive an Editor's Choice award, while the top budget picks score Great Buy designations.
Birder's World magazine also conducts excellent comparative tests of binoculars, with a focus on those that excel for bird-watching. In the magazine's most recent review, 11 testers from a local bird club evaluate eight lightweight binoculars. Every tester evaluates each pair of binoculars and ratings are given on comfort, eye friendliness and optical quality. The binoculars are then rated on a 5-point scale, making it easy to determine which perform the best.
Picking the best binoculars
Binoculars are available in a staggering range of prices. Most reviews cover binoculars costing between $200 and nearly $2,000. When it comes to binoculars costing less than $200, we found user reviews like those posted at Amazon.com to be the best resource. Buzzillions.com and online retailers like Cabelas.com provide a good selection of user reviews for binoculars as well.
We also found solid test-based reviews at publications like Outside, Bird Watcher's Digest and Field & Stream magazines. While the testing process varies with each magazine, usually more than one tester evaluates each pair of binoculars. Bird Watcher's Digest rates the tested binoculars on a 5-point scale; Outside and Field & Stream focus on text-based analysis. There is also a host of good information on binocular websites like AllBinos.com, Optics4Birds.com, BetterViewDesired.com and Birdwatching.com. These enthusiast sites have very detailed single-product reviews, but sometimes contain outdated information. ConsumerReports.org also tests binoculars, but its report is several years old and contains little analysis.
Keep in mind that specifications rarely tell the whole story, even for image quality -- not to mention comfort and usability. Binoculars are a product for which rigorous comparative reviews really matter.