Eye relief is the distance behind the eyepiece lenses at which the image is in focus, and indicates how far the binoculars can be held from your eyes and still allows you to see the entire apparent field of view. In general, the longer the focal length of an eyepiece, the greater is the eye relief. Standard binoculars have eye relief ranging from only a few millimeters to 25 millimeters or more. Long eye relief is especially necessary for the person wearing eyeglasses. This is because the applied eyeglasses increase the distances between the lens and your eye. In case your eyeglasses correct only for near or farsightedness, you can simply take them off and refocus the binocular to compensate.
Most binoculars and spotting scopes have either a folding or twisting eyecup design, so the eyeglass wearers that eyeglass wearers feel the comfort and can bring the binocular in closer to their eye which improves viewing significantly. Some models are particularly designed to give long eye relief (sometimes called "high eye point"). Binoculars with long eye relief usually have long rubber eyecups so that you can also use them comfortably without eyeglasses, also. Generally, a binocular with eyepieces designed for long eye relief will not have a particularly wide field of view so a decision has to be made as to which feature is most important.
Eye Relief and Eyecup Design is also the most important part and aspect while choosing the binoculars for yourself as these provide you a sense of relief and a hassle free quality viewing.
