EYECUPS The eyecups of binoculars or the extension on top of the binocular focal eyepiece (the lens you look through) are normally made of rubber and are called "rubber eyecups". Some binocular manufacturers have switched to or installed 'metal' or 'plastic' eyecups on their binoculars as a selling point and say these will last longer rubber eyecups and are easier to operate. Binocular rubber eyecups are designed to be 'folded' or 'rolled' down while metal eyecups are designed to be 'twisted' up or 'pop' up. It makes no difference which kind of eyecups your binoculars have as far as the intended purpose of the binocular eyecups is concerned.

SHADE/COVER The first purpose of the binoculars eyecups is to provide shade or cover from sunlight, either direct or indirect, between the eye and the binoculars eyepiece. Providing shade or cover between the eye and the binoculars eyepiece greatly enhances the clarity and sharpness of the object being viewed through the binoculars by reducing glare onto the focal lens of the binoculars and the eye. Binocular eyecups should always be in the 'up' or normal position when viewing through your binoculars if you are not wearing glasses. If you are wearing glasses for corrective vision or sunglasses and do not want to remove them before viewing through your binoculars, fold or twist the binoculars eyecups down before viewing. This will bring the binoculars closer to your eyes while providing the approximate eye to lens stand-off of the binoculars (discussed in the nest paragraph). When the binoculars eyecups are in the down position for glasses use, the binocular eyecups provide very little shade/cover from outside light sources.

STAND-OFF Binocular stand-off is referred to by binocular manufacturers as "eye relief". This is the distance from the eye to the focal lens of the binoculars that offers the greatest ability of the binoculars 'full field of view" in millimeters when held that distance from the eye. Example, Eye relief = 15mm. Eye relief can range anywhere between 5mm to 20mm depending on lens diameters. Most binocular manufacturers design their eyecups, whether rubber, metal or plastic to a length that offers the approximate eye relief distance designated in their specifications. In other words, if the binoculars eye relief is 15mm, the binoculars eyecups are normally 15mm in length from the eyepiece lens to where the eyecups will touch your eyelids or brow, creating a 15mm stand-off for the optimum field of view of the binoculars.

GLASSES WEARERS If you wear glasses it is recommended that you remove your glasses when viewing through your binoculars if your vision is such that you can focus clearly without them. For most people that wear glasses this is no problem but for some, especially those with astigmatisms, this is not always the best situation for clear, sharp binocular viewing. Viewing through your binoculars without your glasses when you can still focus clearly will offer you the best viewing through your binoculars as far as eye relief/stand-off and light glare are concerned.

Company Resource: Monocular Telescope , Waterproof Binoculars, Promotional Binoculars