How to Focus Binoculars Properly

Proper Focus Means the World When Being Outdoors

I know most of you already have binoculars, but one of the most common problems I find is that people don't really know how to focus them properly for their myopia (eyes with different sightedness). All of us have different eyes, we see better in one eye than the other, one is near sighted or one is far sighted, one needs contacts and another doesn't. All of this translates into needing to be able to adjust your binoculars properly when birding or out looking for wildlife. I can't tell you how many times I've taught classes, of adults and children alike, and no-one knew how to focus properly. They thought that it was a matter of simply looking through through the binoculars and turning the knob until everything looked clear.

If you want to know how to choose the right pair of binoculars for you check out this page from the Best Binoculars and Binocular Review Website http://www.bestbinocularsreviews.com/guides/.

A good pair of binoculars should be at least 7x32 or 8x32. The first number is the magnification and the second is the size of the diameter of the front of the lens in millimeters. When choosing binoculars for outdoors I tend to like those with armor and fog proofing as well as glare reduction.

Step 1: Know the anatomy of your binoculars.

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Mirador binoculars are what I use 8x42 (pictured above, beaten up from years of use)

When you're choosing your binoculars it's important to consider focusing for your particular eyes. The wheel in the middle of the binoculars is called the 'fly wheel." When you turn the fly wheel BOTH of the barrels of the binoculars move. This type of adjustment is a form of focusing, but it does not calibrate the binoculars for your eyes.

To calibrate specifically for your eyes most quality binoculars have a diopter ring around either the left or right ocular (piece you look through), most commonly on the right. The diopter may also be in the middle, on the fly wheel, but it's most often on the ocular (If the diopter is on the fly wheel it usually affects the right ocular). The diopter allows you to focus ONE barrel at a time, so that you can adjust the focus, and make up for the difference between your right and left eye's visual range. This is particularly important for those that are near sighted or have a visual acuity difference in their eyes.

The diopter can be identified by looking for a ring, or piece of the ocular that has a plus and minus on either side of a 0 or arrow (see picture below).

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Step 2: Calibrate the diopter

You should only need to do this once, unless the diopter gets moved or someone else borrows your binocular and changes the settings.

  1. Without using your binoculars locate a subject that is approximately 30 feet away from you (~10 m).
  2. Bring your binoculars up to your eyes. Close the eye that has the diopter, usually the right, and use the fly wheel to bring your object into focus for the left eye.
  3. Now open both eyes and place your right hand on the diopter. Close your left eye and use the diopter to bring the object into focus, by turning it left or right.
  4. Open both eyes and you should have a clear focus and calibration for your eyes.

Some higher end binoculars have diopters that can be locked into place once the proper settings are achieved, please see your manual for these instructions.

When choosing binoculars it's best to consider choosing higher quality binoculars with diopters that can be adjusted. For those with glasses it's important to consider the plastic eye pieces that are on each ocular. It's best to try out binoculars in the store, and make sure that the eye pieces, and their rings, fold down so that if you wear glasses you can fold down the rubber and get your glasses closer to the ocular.

 
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About Infinite Spider

My name is Karen and I am currently the Education Program Coordinator at the Smithsonian Environmental Research Center, working with students K-gray and doing outdoor science education based on Smithsonian research. I have also been a curriculum developer for the Smithsonian Science Education Center and a contract curriculum writer for the Discovery Channel. In my spare time I love to explore nature topics that I want to know more about, which has lead me to blogging here on "The Infinite Spider" (Infinitespider.com). I've designed it to be a science and nature blog for every-day people, naturalists, and outdoor educators. Currently I live in Annapolis, MD. If you have questions you can reach me at greathornedowl76@gmail.com. Let me know if you enjoy the blog or if you would like to see a particular topic covered. Thanks for reading!