Focusing of Binoculars
There are two basic types of focus systems on binoculars: center and individual focusing. Center focusing is the most common and convenient and generally the most preferred as both eyepieces can be focused simultaneously. Individual focus, which allows for extra-precise focusing adjustments, is often associated with waterproof binoculars which are used primarily for marine use or for astronomy where the focus distance is seldom changed. Most observers prefer binoculars that have a slower focus rate which permit very precise, fine focusing. On center focus models, a separate diopter adjustment on one eyepiece (usually the right one) allows compensation for the differences in the strength of each eye.
The ability of a binocular to focus closely is a much desired characteristic for many situations such as, critical identification of birds in the field or observing the intricate detail of insects or plants, for example. The close focus distance of a particular model depends on its optical design and to some extent, on the individual's own eye characteristics. A minimum distance of 18 to 20 feet is usually acceptable but many birders prefer models that are capable of a near focus of 8 to 13 feet.
Thanks to our friends at Eagle Optics for providing this information!
Back to Bird Watching Binoculars