OWL Nature/Birding Products
There are a number of factors that should be taken into account when you choose a pair of binoculars. It does not help the confusion when several of the different features you might want in binoculars work in opposite directions. As an example, you want an adequate aperture (diameter) but large aperture binoculars can be heavy. While there are a lot of different opinions, we will give our opinion to add to the confusion.
Assuming you are not going to observe birds in a blind and wait for them to come to you, you want a fairly light weight and compact pair of binoculars. Basically there are two major types of binoculars used for bird study. This is based on the types of prisms used.
|Types of Binocular Prisms|
|Roof Prisms||Poro Prisms|
|(Appears to be straight through view)||(Appears to be offset view)|
The size of binoculars are usually given as two numbers with an "X" between them. The number before the "X" is the power. The number after the "X" is the diameter of the main lens in millimeters. A 8X42 means that the binoculars are 8X (8 power) and have a 42 mm lens. At first glance it might seem that the higher power the better, but this is not quite true. If you are going to hand hold the binoculars (not use a tripod), the view through high power binoculars tends to wiggle all over the place. They also are dimmer than lower powers because all the available is divided up as the size of the image increases. For binoculars you are going to carry with you and use in some rough terrain, you should keep the power in the range of 7X to 12X. And 12X is probably too high in many cases.
The other part of the value that represents the diameter of the lens also must be considered. Because front lens gathers the light, the larger the front lens (for any given power) the brighter the image. The brightness goes up with the square of the diameter. A 50 mm lens gathers 4 times as much light as a 25 mm lens. But the problem with this is that the larger the front lens, the more the binoculars weigh. I always carry a 21 mm super-compact pair of binoculars on a belt loop or in my pocket and take a 42 mm or 50 mm as my main binoculars into the field.
There are 2 features of binoculars to look for. One of the most important is coatings. All glass reflects some light rather than passing all of it through the lens in your direction. Standard anti-reflection coatings save you most of this light. The best coatings of this type are what is called "multi-coatings." Standard anti-reflection coated surfaces will reflect about 1% of the light. The multi-coated lens surfaces will reflect about 0.2% of the light. The red coatings are good for glare such as on water or snow. They are not the best for birding.
There are currently 2 types of materials that the prisms are made from. These are called BAK-7 and BAK-4. The BAK-7 was the deluxe prism material until a few years ago. The newer BAK-4 prism material is even better. It gives better contrast.
As with lenses, there are 3 types of coatings for prisms. The standard anti-reflection and the multi-coatings are the best know types. The multi-coatings are the better again. A very few of the most modern (and expensive) binoculars have what is called "phase" coatings. These are the best but are expensive.
While it is optional, it is a good idea to have binoculars that are waterproof (actually water resistant). This keeps your binoculars safe in a rainstorm or on damp, dewy mornings. This will add to the cost of the binoculars, but is a good idea. The best kind of binoculars of this type are filled with dry nitrogen and sealed. This dry filling nitrogen also keeps the inside from forming dew or frost on the inside are really cold days.
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Last Updated August 10, 2007 (Eastern Time Zone)