Field of View and Focus Distance
Field of view
Field of view is the width of the area you see while looking through your binoculars. It is usually expressed as the width in feet of the area visible at 1,000 yards from the observer, although some binocular manufacturers give field of view in degrees.
The wider the field of view, the easier it is to locate birds with your binoculars. Wide-angle binoculars are especially useful for beginning bird watchers, because the larger field of view makes it easier to find birds. Extra-wide-angle binoculars provide an even broader field of view by using more and larger lenses in their optical system, but this makes them expensive and heavy. Beware of inexpensive extra-wide-angle binoculars; they are probably sharp only in the center of the field. Many experienced bird watchers find that a standard field of view is adequate for most situations and that extra-wide-angle binoculars are unnecessary.
If your bird watching tends to be at close quarters, or if you like to study butterflies as well as birds, close-focusing binoculars may be a good choice for you. A number of modern models, usually roof-prism designs, can focus as close as four feet.