Eye Relief of Binoculars
Eye relief refers to the distance behind the binocular eyepiece at which the whole field of view is clearly visible to the observer. With binoculars, this distance will vary from as little as 5mm to as much as 23mm and it is a very important specification for those who prefer or need to wear eyeglasses or sunglasses. Unless a binocular has a minimum eye relief of about 15mm, there will be some difficulty in comfortable observing and in seeing the complete field of view when wearing eyeglasses. If an individual's eye correction is for near or far-sightedness then the binocular's focusing travel will usually accommodate for this without the need for wearing the eyeglasses. However, for moderate to severe astigmatism it is almost a necessity to wear them for serious observing.
Most modern binocular models have fold-down rubber eyecups so that eyeglass wearers 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.
Thanks to our friends at Eagle Optics for providing this information!
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