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How To Buy Binoculars

Binoculars can be used for a host of outdoor and indoor activities, from bird watching to football games, to concerts. No matter what activity you use them for they will always serve the same purpose: to improve your view of a distant subject. However, how you plan to use your binoculars, and where and when, are critical to the binocular selection process.

  • How to buy binoculars
    • Magnification/Lens diameter
    • Brightness
    • Prisms
    • Field of view
    • Focus
    • Selecting the right binoculars

How to buy binoculars

The pair of binoculars you buy will probably end up lasting you a lifetime. Therefore, it is important to take a look at all the different features in order to determine which features are really important to you.

Magnification/Lens diameter

  • Every pair of binoculars has a reference number that tells you its magnification power. A standard number would be 6 x 30.
  • The number 6 refers to how many times the binoculars will magnify an object; in this case, it will appear 6 times closer than it really is
  • As a general rule, higher magnification will make it more difficult to pick up moving objects, such as birds
  • The 30 number indicates the diameter of the front of the binoculars, or the objective lens
  • The objective lens gathers the light that will eventually reach your eyes
  • In general, a larger objective lens means more light will be let in the viewing area, also known as the field of view, and it will be larger
  • A larger lens diameter; however, does mean a heavier pair of binoculars

Brightness

  • Binoculars come with a variety of brightness levels, which is basically the amount of light your binoculars let in
  • The primary deciding factor in determining brightness is the size of the exit pupil, which is the size of the beam of light your binoculars allow in
  • A larger exit pupil will allow in more light, which is a benefit if you plan to use your binoculars in lower light conditions but not as desirable if they will be used outdoors in the sunshine
  • To determine the size of the exit pupil, divide the lens diameter by the magnification power
  • A 3-mm to 5-mm exit pupil is generally adequate for normal viewing. A 7-mm is best for low-light use.

Prisms

  • The purpose of a prism in binoculars is to correct the inverted and reversed images you would see in their absence
  • The prisms are located inside the binoculars and they transmit light from the objective lens to the eyepiece
  • Binoculars come in two prism designs: porro prism and roof prism
    • A porro prism offsets the eyepieces from the objective lens to allow more brightness to be let in. However, this makes the binoculars larger.
    • A roof prism aligns the lenses in a straight configuration, which makes the design smaller. This preferred size is a consideration, but the image is not as bright as with a porro prism.
  • Most binoculars have a standard BK-7 prism glass

Field of view

  • This is the measure of how much you can see through your binoculars at 1,000 yards
  • Generally, the higher the magnification, the less the field of view
  • This information is always printed either on the instruction sheet or directly on the binoculars
  • The field of view for a 7x binocular is usually 7 degrees, or 369 feet
  • A wider field of view, up to 9 degrees, is considered a wide-field model and is best for wildlife viewing

Focus

  • There are generally three focus features on each pair of binoculars
  • Some binoculars offer fixed focus, which is convenient but loses the ability to alter the focus for personal needs
  • A center knob lets you focus both barrels at the same time
  • The right diopter ring, located on the right eyepiece, allows you to customize your focus for each eye
  • Binoculars are also ranked on near-focus distance, which is simply how far away you must be from your subject before it can be properly focused. The general range is 10-40 feet.

Selecting the right binoculars

  • Use the following guide to help choose the proper magnification for your binoculars:
    • Indoor sporting events, theater/opera: 6 x 30
    • Hiking, light bike touring, nature walking: 7 x 25
    • Outdoor sporting events and concerts, boating, wildlife observation, general purpose: 7 x 35
    • Star watching, hunting, bird watching, general purpose: 7 x 50
    • Long-distance bird watching, star watching: 8 x 40

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