What is the eye relief for binoculars?

Eye relief is the distance (in millimeters) that a binocular can be held from the eye while the full field of view can still be comfortably observed. It measures the spacing from the last surface of the eye lens (the lens closest to your eye) of an eyepiece to the plane behind the eyepiece where all the light rays of the exit pupil are visible. Your eye should be positioned here to see the full field of view of the eyepiece.

Eye relief should be at least 10 mm. For the best comfort, look for an eye relief of 15 mm, maybe more if you wear eyeglasses.

To test eye relief, hold your binoculars so they are just in front of your eyes to take advantage of its eye relief. You’ll lose field of view if you place your eye farther away and may even move your eye out of the beam of light from the eyepieces. Getting too close will prevent you from blinking and may also cause a black ring to appear around the field of view.

Updated 10/23/13