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The Binocular Advisor

Birding Binoculars

Part 6

Eye Relief and Birding Eyeglasses

Eye relief is how far back from the eyepiece your eye can be and still see the whole field of view. It is the most important consideration for eyeglass wearers, because glasses hold the eyes back from the eyepieces. If the distance to your eyes is greater than the binoculars' eye relief, you will see only the center part of the image. It's like paying for a box seat but watching the game through a hole in the fence.

Normal eye relief for binoculars ranges from 9 to 13 mm. Even though the eyecups of most binoculars fold down to let glasses wearers get closer, in many cases, it's not close enough. If you wear glasses, you need binoculars whose eyepieces are specially designed with long eye relief, which manufacturers describe as 14 mm or longer.

It's odd that eye relief specifications are often left out of brochures and catalogs, since the eye relief number is the best way to compare models for use with glasses. To measure eye relief yourself, point the binoculars' objectives at a bright light source and move a paper back and forth near the eyepieces. The eye relief is the distance from the eyepiece at which the circle of light comes into sharpest focus. This is the optimal place for the eye to be. It's called the eyepoint.

If your binoculars' eyepoint is not compatible with your eyeglasses, you are missing the big picture, a lot of the fun, and possibly the bird.

Birding eyeglasses
You may find it helpful to buy a special pair of birding eyeglasses that let your eyes get closer to the eyepiece. For example, my "spare" eyeglasses sport old-fashioned wire-rim frames. The lenses are much smaller and lighter than my regular frames. They bring my eyes closer to the eyepieces than my regular glasses and give me more choice of which binoculars I can use. I can even use 10 x 25 pocket binoculars without feeling as if I'm trying to look through a pair of soda straws.

If your regular prescription includes bifocals, ask your optician to move the dividing line as low as possible, so that you can look over it when using your binoculars. Don't be tempted to eliminate the lower bifocal entirely. You will regret it the first time you try to read your field guide.

The anti-reflective coating technology used on binocular optics is also available for eyeglasses. It increases light transmission when using your glasses with binoculars. It will also improve visual comfort, especially at night, while working under fluorescent lighting, or when using a computer. Once you try it, you'll want it on your regular frames too.

—Michael and Diane Porter

birdwatching.com

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Need Specific
Recommendations?

If you're about to get some new binoculars but don't quite know where to start, check out the Binoculars Advisor for specific, name-naming recommendations.

Michael and Diane Porter, who have been reviewing binoculars for Bird Watcher's Digest for over a decade, suggest binoculars for particular needs and price ranges.