Do you take lots of pictures outdoors? Do you often shoot scenic vistas, landscapes, wildlife, birds, or sporting events?
Do you bring your camera along when you go vacationing, hiking, fishing, boating or hunting? If you answered yes to any of these questions, you should definitely own a good binocular. Binoculars are a great way to locate, observe, and select the best subjects to photograph, or simply to appreciate the glories of the great outdoors.
We photographers are visual folks who appreciate fine optics, and, next to photographic lenses, binoculars are the handiest, most widespread of all optical instruments. Indeed, some of the very best binoculars in the world carry familiar photographic names like Nikon, Canon, Olympus, Pentax, Leica, and Zeiss! Don’t overlook other established brands like Bushnell, Leupold, Celestron, and Swarovski--all mainstays among the camping, hunting, and outdoor set.
To help you select the best pair of binoculars for your particular use, this week we’ll learn Binoculars 101, and will provide you with a useful guide to the best binoculars for specific uses. For those who want more technical detail, we’ll post a glossary of binocular terms on Friday.
Binoculars 101: Basic specifications
The most essential specs for binoculars are magnification (power) and the objective (front) lens diameter, which affects the brightness of the viewing image and suitability for low-light applications. The first number in the designation “8x25” (right) or “7x50” is the magnification, the second is the diameter of the front lens in millimeters. Zoom binoculars (e.g. 7-15x50) offer variable magnification.
You can calculate the size of the exit pupil by dividing the front lens diameter by the magnification. It’s important because it determines how much light is available to be transmitted to your eyes, For example, a full-sized 7x50 binocular has an exit pupil of 7.1mm, roughly equal to young, dark-adapted human eyes, so it’s an excellent “night glass.”
A compact 8x25 binocular has an exit pupil of only 3.1mm, which is fine for daylight viewing, but will limit what you’re able to see when the light gets really dim. The higher the power of a binocular, the harder it is to hold a steady image, so stick to magnifications in the 6-10 range unless you opt for a large, expensive high-powered model with image stabilization.
Without proper eye relief (it varies from about 5mm to 23mm), eyeglass wearers will not be able to see the full field of view, so make sure you can see the whole viewing image, out to the circular rim.
Internal focus is an important feature for waterproof binoculars because it minimizes the ingress of water dust, and fog.
Make sure the binocular you buy can accommodate the interpupillary distance or ID (it’s the distance between the pupils of your eyes) of anyone who will be using it much—kids can be a problem. Do an in-store check before making your final choice.
Examine several binoculars and note any differences in quality of construction, finish, and smoothness of the controls. Examine the lenses under bright light and favor those that look darkest, a sign of quality coatings that enhance light transmission. Hold the binoculars at arm’s length, point the front lenses toward the light, and look into the eyepieces.
Reject units that show circles of light with rounded corners or odd shapes in the eyepieces. Finally, check for proper optical alignment by viewing a distant scene. What you see through each of the two lenses should look the same, and your eyes should be able to merge them into a single image without effort or strain.
All About Prisms
The two types of prisms used in binoculars are roof prisms and porro prisms.
Roof prisms are positioned one behind the other, so roof prism binoculars have straight tubes, and are generally more compact and rugged. Porro prism binoculars, such as the Leupold 8x30 Yosemite model at right, have offset tubes, with the front lenses positioned either closer or farther apart than the eyepiece lenses, and may provide more of a “3D” look to the viewing image.
In the past, only the most expensive roof prism binoculars such as the Pentax 10x50 DCF ED (left) gave first-class performance and porro prism binoculars offered far better quality in the medium-priced range. However due to improvements in manufacture and phase coating, today’s best compact roof prism binoculars in the $200 range and full-sized models in the $300-600 range can provide image quality nearly on a par with premium-quality binoculars, which retail for $500-1.000 in compact models and $1000-$2000 and up for full size models with special features.
If high performance is important to you, make sure the binocular you buy has BaK-4 prisms (BaK-7 prisms are not as good) and fully multicoated optics.
Learn more about binoculars