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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.
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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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