Binoculars Basics - What to Look For When Buying
By Elizabeth Hart
Not all binoculars are created equal. Different features are important for varying activities: traveling, hunting, birdwatching, etc. For instance, travel binoculars need to be light and compact and magnification needs to allow for handheld use without a stabilizer. For hunting and fishing a "bright" lens is needed - one with a large objective lens.
Porro Prism vs Roof Prism
One thing to consider when choosing a binocular is the design. There are two styles of binoculars: Porro prism and Roof prism. The large difference between these two is size and transmittancy. The roof binocular is more compact, with a classic "H" design while the porro prism is more bulky. While the porro prism binocular is generally less expensive, the roof prism design has become more popular due to the higher light tranmittancy.
Important binocular nomenclature:
Lens Coating - Air-to-glass prism surfaces often have an anti-reflection coating that assists the light transmission. Multiple layers of coating are approximately 1 magnitude more effective than a single layer.
Collimation - The optical and mechanical alignment of the binoculars. Note: Cheap binoculars are sometimes shipped from the manufacturer out of collimation. If a pair of binoculars is out of collimation, after prolonged use it may feel as though your eyes are being sucked out of their sockets. High end binoculars are usually collimated with laser instruments before leaving the manufacturer - increasing the retail price.
Magnification/Power - The power is how many times closer the object you are looking at will appear through the binoculars. Common magnifications are 6x, 7x, 8x, 9x, and 10x. The higher the magnification, the more steady you must hold the binoculars.
Objective Lens - The lens that allows light to enter the binocular.
Field of View (FOV) - As it sounds, FOV is the area seen through the binoculars and is measured in degrees or 'feet at 1,000 yards'. This number is important to look at when using to observe moving targets - whether animals in nature or at sporting events.
Binoculars are often decribed by a pair of numbers, such as 8 x 36. The first number is the magnification and the second number is the diameter (in millimeters) of the objective lens. In this example the power is 8x and the diameter of the objective lens is 36 mm.
The size of the objective lens is important because the larger the lens, the more light is allowed in. Therefore, in dim lighting a larger objective lens will work better. Also, the larger the objective lens, the longer the binocular tube has to be to allow the image to focus.
When looking to buy binoculars, you must balance the power with the size of the objective lens. As mentioned above, binoculars to be used for travel may not be the best to use for hunting.
A Quick Guide: