Choosing a Binocular
Selecting the right binocular is a matter of picking the best combination of features for your particular needs, including magnification, bulk and weight, brightness, field of view, optical quality, and cost.
Binocular sizes are expressed with two numbers: 7x35, 10x50, etc. The first number is the magnification (or power), the second is the aperture, or diameter of the objective (front) lenses in millimeters. For example, 7x35 binoculars provide 7-times magnification and have 35mm objective lenses. For a given magnification, larger objective lenses yield a brighter image in dim light, but also result in a bulkier, heavier binocular.
The higher the power, the "shakier" the image will be, because small hand movements get magnified. Therefore, we recommend a binocular of moderate 7x or 8x magnification unless you have a specific need for more power. Lower-power binoculars also usually offer a wider field of view, allowing you to take in more of a scene at one time.
What Will You Do With it?
Hiking If you hike or travel a lot, you'll want a binocular that is compact and lightweight, perhaps even weatherproof. An 8x24 or 10x25 would be a good choice.
Birding The most popular models for birdwatching are 8x40 and 8x42. They're small and nimble, offer steady hand-held views, and have sufficient light grasp to provide bright, well-resolved images. If you plan to study birds at close range, look for a binocular with a near-focus distance of a few feet.
Astronomy For stargazing, light grasp is the most important factor. Choose a binocular with at least a 50mm aperture. A 7x50 model is easily hand-holdable and provides nice, wide-field views of starry swaths. The higher-power 10x50 is also popular, and in fact is preferable to the 7x50 where skyglow is a problem. A tripod is recommended for a steady view, however.
"Giant" binoculars of 70mm, 80mm, or 100mm aperture will reveal fainter deep-sky objects and more subtle detail. If you can afford the higher price (and a good tripod) and don't mind the extra bulk, you'll be rewarded nightly with incredible views.
Of course, other factors should play into your buying decision too, such as eye relief, optical coatings, and mechanical construction. If you need advice, give us a call!
Binocular Prisms: Porro Vs. RoofThe prisms in binoculars turn what would otherwise be an upside-down image right-side up. There are two main types of prism systems used in modern binoculars: porro prisms and roof prisms.
Porro-Prism Binoculars
Each barrel of a porro-prism binocular contains two right-angle prisms. They are offset from each other, which requires that the objective lenses be spaced farther apart than the eyepieces. Thus, porro-prism binoculars are bulkier than their roof-prism counterparts. Optically, however, porro-prism binoculars usually perform better, because the prism design requires less strict tolerances. That makes them easier to manufacture, so they cost less. Also, porros yield a more stereoscopic, or three-dimensional, image.
Roof-Prism Binoculars
The prisms in a roof-prism binocular overlap closely, allowing the objective lenses to line up directly with the eyepieces. This results in a more streamlined, compact, and often more lightweight binocular than equivalent porro-prism models. But roof-prism binoculars are also more difficult to manufacture, so they cost more. Roof prisms lose slightly more light to reflection than porro prisms — a disadvantage for astronomical use but not a concern for daytime terrestrial viewing. Well-made roof-prism binoculars can provide optical performance nearly equal to, but not better than, porro-prism binoculars.
Prism Glass
Most optical prisms are made from either BK-7 (borosilicate) glass or BAK-4 (barium crown) glass. BAK-4 is the higher-quality glass and yields brighter images and better edge sharpness. It is also more expensive.
Field of ViewThe field of view is the size of the "window" you see through a binocular. The field has no effect on the size of the subject being viewed (that's a function of the magnification). Surprisingly, the field of view is not determined by the binocular's main (objective) lenses, but rather by the eyepiece and prism designs.
The width of the field is expressed either as an angular measure in degrees, or as a linear width, in feet, of the viewing area at a distance of 1000 yards. You can convert from angular field to linear field by multiplying the angle in degrees by 52.5.
"Wide-angle" is an inexact term that simply indicates that a binocular field is wider than average. Generally, a binocular is considered wide-angle if its apparent field of view (angular field in degrees times magnification) is 60 or greater.
A wide-angle binocular is ideal for finding subjects quickly, and it can deliver spectacular panoramic views. A wide field is especially desirable for watching action sports or scanning to pick up motion at close range, such as in a wooded area. A narrower field of view is sufficient for longer-distance observation.
Of course, we're here to help should you need more assistance in choosing a binocular. Just give us a call Toll-Free at (800) 676-1343! Or use our Smart Buy Advisor to help you find a binocular that fits your needs and your budget!
