What is eye relief in binoculars?

Eye relief refers to the distance between the eyepiece lens and the eye at which the full field of view can be seen without any vignetting or loss of clarity. It is particularly important for individuals who wear glasses or have astigmatism, as it allows them to see the full image even when their glasses are on.

In binoculars, eye relief is measured in millimeters (mm) and typically ranges from 8mm to 20mm. A higher eye relief is beneficial for people who wear glasses because it provides a larger space between the eye and the eyepiece, allowing them to comfortably see the entire field of view. Eye relief below 10mm may lead to a restricted view where only the central portion of the image is visible.

To determine the appropriate eye relief for you, it is recommended to try different binocular models while wearing your glasses (if applicable) and adjust the eyecups to find the ideal position for comfortable viewing. Some binoculars also have twist-up or fold-down eyecups that can be adjusted to accommodate both glasses wearers and non-glasses wearers.