Binoculars and eye fatigue
Posted by Joannie K on May 25, 2011
Are your binoculars giving you eye fatigue and eye strain? If the answer is yes, it could be a problem with your binoculars, but it could also be a problem with how you adjust and are using your binoculars. Either way, binoculars and eye fatigue is a bad combination.
Your binoculars, of course, can be the source of that eye strain and fatigue. The culprit, here, is misalignment of the prisms inside the binocular housing. In order to achieve strain free viewing in a binocular, those prisms must be aligned to be looking at the same point out in front of the binoculars at a given distance. Close does not count, either; in roof prisms a prism that off a fraction of the width of a human hair can cause eye strain. The good news, here, is that most binoculars, by far, are correctly aligned right out of the box. Once in awhile, though, one slips through quality control that is not correctly aligned. This is much more likely to happen with cheap binoculars, since using minimal quality control is a way to keep prices down. It is also more common on large astronomy binoculars because the large barrels on these binoculars have a tendency to flex, allowing the prisms to work loose. The bad news, here, is that you can’t adjust and align prisms on your own (there are some exceptions, such as certain Oberwerk astronomy binoculars). Time to send the binoculars in for repair.
There are some things you can do, though, to eliminate some sources of eye strain. First, make sure that diopter adjustment is correct for your eyes and spend some time getting it right. Keep both eyes open when adjusting and if that is a problem, place your palm over one barrel as you make your adjustment. Squeezing one eye shut as you make the diopter adjustment will give you an incorrect adjustment because closing one eye produces eye strain and distortion that will not be there when you open both eyes, as you will do when using the binoculars, of course.
Speaking of squeezing, squeezing the eyes or squinting of any kind when using binoculars will also produce eye fatigue. Some of us do this subconsciously. I know I do. If you do it, too, make a point of opening those eyes wide and making them relax as you use your binoculars, almost as if you are about to go to sleep. You will be surprised at the difference. In other words, make the binoculars do the work, not your eyes. At the end of the day, your eyes will thank you.
