Wearing Glasses With Binoculars: Eye Relief and Twist-Up Eyecup Setup

For people who are nearsighted, the most common complaint about binoculars is that the center of the image looks clear while a dark ring surrounds it. This is not a fault of the binoculars. Your eyes are simply too far from the eyepiece: the frame of your glasses gets in the way, so your eyes cannot move close enough to the exit pupil position.

This brings up a key specification: eye relief. It is the distance your eyes need to be from the eyepiece in order to see the complete image. Eye relief on binoculars is generally designed to fall between 10 and 20mm. If you do not wear glasses, you can rest your eyes right against the eyepiece. If you do wear glasses, the frame alone takes up more than 10mm, so it is easy to come up short.

The solution lies in the eyecup. A twist-up eyecup exists to adjust exactly this distance. If you do not wear glasses, twist the eyecup up and rest your eye socket against it for a proper fit. If you do wear glasses, twist the eyecup all the way down so the lens sits against the lens of your glasses.

Here are three steps. First, find out the eye relief specification of your binoculars; it is usually listed in the user manual or on the product page, and 18mm or more counts as a long eye relief design that is friendly to glasses wearers. Second, when you wear glasses, twist the eyecup all the way down. Third, look at the image: if dark corners remain around the edges, the eye relief is not sufficient, so you need to bring your eyes closer or switch to a long eye relief model.

Another approach to observing with glasses is to take them off and use diopter compensation. The right eyepiece of a pair of binoculars, and the eyepiece of many monocular telescopes, has a diopter adjustment ring that can compensate for nearsightedness. Take off your glasses, focus clearly with the diopter ring, and from then on observe with the naked eye. The advantage is a complete, unrestricted field of view. The drawback is that every time you hand the binoculars to someone else, the setting has to be adjusted again.

If your prescription is mild, within about two or three hundred degrees, it is worth trying the diopter compensation route first; in many cases the experience turns out to be better. If you are highly nearsighted or have noticeable astigmatism, wearing glasses and twisting the eyecup down is still the easier option.

In one sentence: when you use binoculars with glasses, twist the eyecups down first, then check the eye relief specification, and anything 18mm or above is fine to choose. If dark shadows remain around the edges, it is time to switch to a long eye relief model.