No matter what activity you pursue, from hiking to paddling or bird-watching, make sure to choose binoculars that will suit your needs and magnify your enjoyment.
Facts at a Glance
- Choose compact binoculars if weight/size is a primary concern. Full-size binoculars are heavier, but typically outperform compact models in low-light conditions.
- Binoculars are identified by two numbers, such as 7 x 35. The first is magnification power; the second is diameter (in millimeters) of the objective lenses (the front lenses).
- Exit pupil refers to the diameter of the shaft of light that exits through each eyepiece and reaches your pupils. For dusk or dawn viewing, get binoculars with an exit pupil of 4mm or more.
- Field of view tells you the width of the area you can view in one glance, 1,000 yards from where you stand. In general, the higher the magnification the smaller or narrower the field of view.
- Eye relief describes the distance behind the eyepiece at which the whole field of view is visible. If you wear glasses look for an eye relief of 11mm or greater.
No single factor determines that one set of binoculars is superior to another model. Your personal preferences and intended usage will determine which pair is best for you.
This article will break down the various factors to be considered when selecting binoculars. At its conclusion, we'll compare and contrast the importance of these factors and, we hope, guide you to a pair that serves your needs best.
Cost and Quality
When shopping for binoculars you'll discover wide price ranges on similar-looking models. The old axiom "you get what you pay for" rings particularly true with binoculars. Prices usually correspond to the quality of the optics. As you might expect, better optics mean better-performing binoculars.
Compact or Full Size?
Mention binoculars and the classic image that typically comes to mind is a pair of traditional, full-size binoculars. (Why, you ask, are binoculars referred to as pairs? Binoculars, an "adjustable optical instrument" by definition, use two parallel telescopes mounted on a single frame. This consolidated device then magnifies distant objects and draws them closer to us in stereoscopic vision.)
Compact binoculars are sophisticated, power-packed devices that have become very popular with self-propelled outdoor travelers.
What are the advantages and disadvantages?
- add bulk and weight if you carry them in a pack
- feature wider objective (front) lenses, which capture more light and perform better in low-light situations
- usually provide steadier images and a wider field of view
- are lighter and smaller
- work very well during daytime outdoor activities (hiking, paddling, etc.)
Binoculars are identified by two numbers. The first is magnification power, the second is the diameter of the front lenses, explained below.
An example: A 7 x 35 binocular has a magnification power of 7.
A magnification power of 7 means that an object will appear seven times closer than it would to your unassisted eye. For example, if you view a deer that stands 200 yards away from you through 7x binoculars, it will appear as though it were 28.6 yards away (200 divided by 7).
So, the greater the magnification power the better the view, right? Not necessarily. Binoculars with magnification powers greater than 10 can amplify the movements of your hands, making hand-held viewing more difficult.
Objective Lens Diameter
The second number used in binocular identification refers to the diameter (in millimeters) of the objective lenses (those farther from your eyes). A 7 x 35 binocular, therefore, has objective lenses measuring 35mm. The diameter of the objective lenses largely determines how much light your binoculars can gather. If you have two binoculars with exactly the same specifications except for objective lens diameter, those with the larger diameter objective lenses will capture more light. More light means a brighter view, particularly in low-light conditions.
The exit pupil, measured in millimeters, refers to the diameter of the shaft of light that exits each eyepiece and reaches the pupils of your eyes. Calculate this number by dividing the diameter of the objective lenses by the magnification. A 7 x 35 model, for example, has an exit pupil of 5mm (35 divided by 7). Generally, a bigger exit pupil means more light reaches your eyes, producing a brighter image. A large exit pupil also makes it easier to maintain a full image if your hands move or shake. Keep in mind that your eyes' pupil size varies from approximately 2.5 mm in bright light to 7mm in low light.
Tip—For viewing at dusk or dawn, look for binoculars with an exit pupil of 4mm or more.
Some manufacturers refer to relative brightness to indicate the quantity of light that binoculars transmit to your eyes. The higher the relative-brightness number, the brighter the image. This specification serves as a key indicator of how much light will reach your eyes.
Note: Prism type, component quality and optical coatings all affect relative brightness.
Tip—Binoculars with high relative brightness make good choices for low-light viewing.
Eye relief describes the distance behind the eyepiece at which the whole field of view is visible. Longer eye relief increases your comfort by allowing you to hold the binoculars away from your face.
Tip—If you wear glasses, look for eye relief of 11mm or more.
Field of View
This specification tells you the width of the area (usually in feet) that you can view in a single glance, 1,000 yards from where you stand. Usually a higher magnification power results in a narrower field of view.
In binoculars, the body contains prisms that transmit light from the objective lenses to the eyepiece. Keep in mind that while they often carry high price tags, high-quality prisms generally provide excellent image resolution and brightness.
You can choose binoculars with either porro prism or roof prism designs. Here's a comparison of the two types:
Roof Prisms—Prisms are aligned internally, allowing for straight tubes and compact designs. This design provides easy-to-handle binoculars with a high power-to-weight ratio. These features make roof-prism binoculars a popular choice among backpackers and mountaineers. Complicated manufacturing processes mean that roof-prism binoculars can be more expensive than porro-prism binoculars.
Porro Prisms—Since this type of prism is offset from the objective lenses, porro-prism binoculars have thicker, bulkier designs. (Traditional binoculars with that dogleg body have porro prisms.) While not quite as compact as roof-prism designs, porro prisms are used in a wide range of binoculars for all kinds of situations and activities. Porro prisms provide quality images and usually cost less than roof prisms.
Note: You can choose binoculars with prisms made from BK-7 or BaK-4 glass. More expensive, higher density BaK-4 prisms offer slightly better light transmission than BK-7 prisms.
Many binoculars have lens and prism coatings that reduce the amount of light reflected back or dissipated from the lens, thus enhancing the quality of the image. In addition, these optical coatings cut the glare that can cause eyestrain when you use binoculars for long stretches of time. Multiple lens coatings are a sign of quality binoculars.
Most binoculars have center focusing designs. With this type of focus, you first balance the binoculars to match your eyes. Close your right eye and focus the center control; next, close your left eye and fine-tune by rotating the right eyepiece (diopter). From then on, use the center focus to quickly obtain a sharp image.
Note: Some binoculars offer close minimum-focusing distances. This feature magnifies fine details on nearby objects, a handy feature if you plan to use your binoculars in art galleries or museums.( or birdwatching)
Many binoculars offer some degree of weatherproofing. Water-resistant binoculars will operate in light moisture, but will eventually spring a leak if they get dunked. Waterproof binoculars completely block out the elements.
Note: Some binoculars have nitrogen-filled interiors to eliminate fogging and prevent dust from collecting on lens interiors.
Some manufacturers offer zoom binoculars. You can increase or decrease the magnification power of these models depending on your needs. If you're eyeing a bird in a tall tree, high magnification will benefit your viewing. If you're following a herd of elk in a broad valley, lower magnification help you take in a wider view.
Many binoculars feature rubber armor over the housing that absorbs shocks, thus protecting delicate optics from bumps and bangs. The rubber also provides a more secure and comfortable grip.
Compact binoculars (common specs: 8 x 25, 10 x 25) generally provide excellent daytime viewing. Since they're small and lightweight they're your best option for weight-sensitive activities such as backpacking and mountaineering.
Full-size binoculars (common specs: 7 x 35, 8 x 42, 10 x 42) are the better choice for serious wildlife viewing. They often provide a wider field of view and greater brightness than compact models. Full-size binoculars outperform compact models in low-light conditions.
Match binocular features to your activity. Examples: Get waterproof binoculars for use while kayaking. Buy lightweight binoculars for a 1,000-Km hike.