Eye Relief

A: When your eye is correctly distanced from the eyepiece, the entire field of view should be comfortably visible. This minimum distance from the eye to the eyepiece (at which the entire field of view is visible) is your eye relief.

Long eye relief (15mm or longer) permits a comfortable distance from the eye to the eyepiece and even for glasses to be worn while viewing through the eyepiece. Short eye relief decreases the minimum distance between the eye and eyepiece, making viewing less comfortable or difficult for eyeglass wearers.