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Binoculars 101

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By Metro naturalist James Davis

You will only get the most out of your binoculars if you know how to adjust them properly. Many people do not know how to use the adjustable eyepiece and never really see as well as they could with their binoculars. Here are easy, step-by-step instructions for making the four adjustments needed to get the best out of your “binocs.”

Eyecups

Modern binoculars have soft rubber eyecups on the eyepieces that fold down to adjust for eyeglasses. If you use binoculars with your glasses on, fold the soft rubber eyecups down so the end of the eyepiece is as flat as possible. When you are looking through binoculars, put the flat eyepiece right up against the lenses of your glasses. If you are not wearing glasses, leave the eyecups extended. A few types of binoculars have eyecups that screw in or snap in to get flat for glasses.

Hinge

The two halves of the binoculars are joined together in the center with a hinge. This is so you can move them in and out until they are the right distance apart for your eyes. While looking through the binoculars, move them in and out until you have one big, clear, circular field of view. If you get dark patches or crescents in the center or on the sides, they are too close together. You should never see two circles. Keep fiddling with them until you get the best field of view and don’t be afraid to keep adjusting them throughout the day.

Central focus

Hold the binoculars in both hands and reach to the center with a big finger or two and turn the wheel in the middle. This is the central focus. You turn the central focus back and forth every time you look at something new to get the sharpest, clearest image you can.

Adjustable eyepiece

This is the most confusing thing about using binoculars. Almost no one ever explains it on guided bird walks and it is often poorly explained in the instructions that come with binoculars (yes, there were some).

When you use the central focus, you focus the two sides of the binoculars at the same time. However, your eyes are probably not identical. You need to adjust your binoculars so that each side is in focus for each eye at the same time. You do this by using the adjustable eyepiece.

The adjustable eyepiece is the one that turns and most binoculars have it on the right-hand side. It should have a simple scale on the underside of the eyepiece that reads something like “ – 0 + ”. Set the adjustable eyepiece to “0” or the middle of the scale.

(The following instructions are written with the assumption that the adjustable eyepiece is on the right. If it is on the left on your binoculars, interchange all references to “right” and “left.”)

1. Pick something to look at through your binoculars that is sharp and clear and a medium distance away (e.g. a sign on a pole).
2. Make all the other adjustments and focus on the sign with the central focus as best as you can with both eyes open.
3. Close your right eye and use the central focus to get the left eye’s image as sharp as possible. (You will only be looking through the left side of your binoculars as you do this.)
4. Then close your left eye and open your right eye. (Now you will only be looking through the right side of your binoculars.) Don't touch the central focus. Turn the adjustable eyepiece back and forth with your right hand until you get the sharpest image you can in your right eye.

Now, with both eyes open, the object should be in sharp focus. To check, use the central focus to focus on something else at a different distance. Then alternate looking at it with each eye by itself. The image should be in the same sharp focus with each eye. If not, try turning the adjustable eyepiece a tiny bit back and forth to see if you can get it sharper. Sometimes you just have to fiddle a bit with the central focus and the adjustable eyepiece until you get them just right.

When you have the adjustable eyepiece in the right position, look at the scale and remember that setting. This is your basic setting for that pair of binoculars, and you can start with that setting each time you use them. However, many people find that their eyes change from time to time so do not be afraid to keep fiddling with it to get the best image you can.

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