Binoculars Terminology - Best Binoculars For Birding

Fulfilling your bird watching and wild bird identification efforts will be realized by understanding basic binoculars' terminology.

Binoculars Terminology

Power/Magnification and Objective Lens Diameter (example 8x42)

The first number, the Power or Magnification measurement, is the degree that the object being viewed is enlarged. In this example, binoculars with an 8 power magnification will magnify the object 8 times larger than would normally be seen with your eyes. The second number, the Objective Lens Diameter, is measured in millimeters (mm). The objective lenses are the front lenses of the binoculars. The diameter of the lens determines the light gathering ability. A larger lens produces greater light gathering ability and therefore improved detail and image clarity. The power level affects the brightness of an image. A lower power will produce a brighter image.

Field of View

The size of the area visible while looking through a pair of binoculars is referred to as the Field of View. Generally a greater magnification or power will produce a smaller field of view. The angular field of view, expressed in degrees, is indicated on the outside of the binoculars. The linear field of view refers to the area that can be viewed at 1,000 yards, and is expressed in feet. A larger field of view translates to a larger area seen through the binoculars. Depending on your bird watching needs, a significantly larger linear field of view may not be important. Please remember, in most cases, the larger the field of view, the poorer the image clarity becomes, especially around the edges. Bear this in mind when making your choice. Bigger does not always mean better.

Close Focus

Close focus refers to the distance between you and the nearest object on which you can focus while still maintaining a good image and sharp focus. This term is normally applied only to center focus models which may need to focus both near and farther distances. Close Focus distance is a critical issue with bird watchers and observers of close subjects that tend to move around at varying distances quickly.

Exit Pupil

The diameter that of the beam of light, measured in millimeters (mm), leaves the eyepiece of a pair of binoculars is the Exit Pupil. The larger the exit pupil, the brighter the image obtained will be. Having a large exit pupil is advantageous under low light conditions and at night such as astronomical, marine or low light conditions.

Relative Brightness

Gathering and transmitting enough of the available light to provide a sufficiently bright and sharp image define the brightness of a pair of binoculars. Brightness is certainly one factor to consider when determining the best pair of binoculars for you, but is not usually the most important. After all, most of your bird watching likely will be during well lit conditions when birds are active.

Eye Relief

Eye Relief is the distance, measured in millimeters (mm), that binoculars can be held from the eye and the full field of view can still be observed comfortably. Those who wear eyeglass in particular benefit from longer eye relief. Normally a minimum rating of 15mm will be needed for those wearing eyeglasses.

Best Binoculars for Birding

While the ultimate choice is one of personal preference, generally full size binoculars ranging anywhere from 7x30 to 8.5x50 are preferred and considered the most popular range in magnification and objective lens size for bird watching. For instance, binoculars with an 8x42 configuration feature a 42mm objective lens size which provides ample light gathering capabilities in even lower light conditions and an 8x magnification allows you to steady the binoculars much more readily than with significantly higher powers, making the task of bird identification easier. Some birders with steady hands may prefer 10 power binoculars or greater.

Please remember that as you increase the power of your binoculars, less light will be gathered and therefore the viewing field will be reduced as well. It is also very difficult to keep an image steady at very high magnifications using standard hand held binoculars. A tripod is often necessary to steady an image at higher magnifications. A good alternative though for those seeking the option of high power magnification is a pair of binoculars with a zoom feature. This gives you the option of higher magnifications without the limitations of fixed, high power binoculars that can be a bit unwieldy.

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