Alignment in Binoculars

A question of alignment

A birder wrote to us:

My binoculars make me feel like my eyes are being squeezed. After I look away I feel slightly crosseyed. If I use my binoculars for a long time I get a headache. What is going on?

You're describing some of the things that happen when binoculars are out of alignment.

Good alignment

What is alignment?

The binocular is a pair of telescopes mounted side by side, each supplying an image to one eye. But you don't see two images. You see one unified picture. For this magic to happen, the two telescopes have to be parallel to each other. They have to be in alignment.

However, bad things can happen to binoculars. If they're dropped, or knocked, or sat on, for example, the alignment between the two telescopes can be messed up. No longer will they point in exactly the same direction. Then your eyes will strain to bring the two images into alignment, causing strain and headaches.

You usually can't tell just by looking at a binocular whether it is in perfect alignment. That takes very expensive equipment. However, you can check for gross misalignment.

Good alignment

How to check the alignment

Pick out a horizontal line in the middle distance, such as a power line or a roof line. Look at it through your binoculars.

While you're looking through the binocular at the horizontal line, slowly pull the binoculars away from your eyes, about two or three inches.

The image will begin to separate into two smaller circles, side by side, overlapping, or slightly apart.

Notice whether the line your chosen makes one continuous line through both circles. If so, that means the binoculars are at least close to being in alignment.

Binoculars out of alignment

If the two sides of the binocular are badly out of alignment, the horizontal line will step up or down between the two circles.

When binoculars are out of alignment, the two images will be fighting with each other. Your brain and the muscles in your eyes have to strain to pull the two parts into line, to let you see a single image.

The effort to align the image with the muscles of your eyes may be unconsicous. However, the effort is likely to cause a headache. Or it may just make it feel like it's not much fun to look through the binoculars.

How to fix misalignment

If your binocular is out of alignment, you can't fix it yourself. The only remedy is to send it to the manufacturer for repair. Warranties vary from manufacturer to manufacturer. Some cover this sort of mishap. Others do not.

If the binocular is under warranty, the manufacturer may repair it for a small sum or for free. If you try to fix it yourself, or if anyone other than the manufacturer works on it, the warranty will almost certainly be voided. So check with the manufacturer.

Or replace the binocular. If it's not under warranty, it's probably not worth paying to get it fixed, unless it's a very valuable model. You can purchase a new binocular that is in good alignment for less than it might cost to have a binocular realigned.

Note that the cheaper the binocular, the more easily it is likely to get knocked out of alignment. High-end binoculars have higher quality engineering, so they're better able to withstand the normal shocks of a binocular's life without going out of alignment. And if they do get out of alignment, the manufacturer is more likely to be willing and able to fix them.

If you can't figure out how to contact the manufacturer, try calling the business that sold you the binocular. They won't be able to fix it, but they can probably get you in touch with the right party.