How to Adjust Binoculars for Bird Watching, Stargazing & More

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Ornithologist Roger J. Lederer, PhD, shares how to focus binoculars for bird watching and more activities

Co-authored by Roger J. Lederer, PhD and Dan Hickey

Last Updated: December 10, 2025 Fact Checked

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• How to Focus
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• How Often to Adjust
|
• What do the numbers mean?
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• Lens Cleaning
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• Video
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• Q&A

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If you’re trying to birdwatch, stargaze, or see something from far away, you’ll need to make sure your binoculars are correctly calibrated to your eyes. Thankfully, all you have to do is quickly adjust 2 settings—the central focus knob and the diopter dial—to get a crystal clear image. In this article, we’ll show you how to focus your binoculars with insight from ornithologist Roger J. Lederer, PhD, plus share how often to adjust your binoculars, what all those numbers on them mean, and how to clean your lenses for the best view.

How do you adjust binoculars?

Ornithologist Roger J. Lederer, PhD, explains that to adjust your binoculars, close your right eye and use the central focus knob to focus your left eye view. Then, close your left eye and use the diopter ring on the right barrel to focus your right eye. Note that not all binoculars have a diopter ring.

Steps

Section 1 of 4:

Focusing the Binoculars

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1. 
   1
   Adjust the rubber eyecups and twistable eyepieces if you wear glasses. The eyepieces are the lenses you put your eyes up to (and their housing) at the end of the binoculars, and the eyecups are rubber or plastic cups attached to the eyepieces that block ambient light and make it more comfortable to rest the binoculars against your face. More importantly, both of these features control the distance between your eyes and the lenses, which is crucial to getting a sharp, focused view. How you adjust them depends on whether you wear glasses or not:

   • If you do not wear glasses: Turn the eyepieces counterclockwise to raise them from the body of the binoculars. If your binoculars come with eyecups, fit the slightly recessed end of the cups over both of the eyepieces so that they are snug and don’t slide off. Some pairs come with eyecups permanently attached.
   • If you wear glasses: Keep the eyepieces retracted or turn them clockwise to tighten them against the body of the binoculars. Remove the eyecups or roll the extended rubber back so that you can look through the binoculars with your glasses on.
   • Extending your eyecups will allow you to fit them around your eye, which will block out the light you’d normally see in your peripheral vision. Some cups have an outer “wing” to block even more light.
   • Retracted eyecups will give you a wider field of view, so you may want to turn them clockwise if you're trying to see a wider image.

   Meet the wikiHow Experts

   Roger J. Lederer, PhD, is an ornithologist and the founder of Ornithology.com. He has spent over 40 years teaching, studying, and writing about birds, including using binoculars to observe them in the wild.
2. 
   2
   Grip both barrels and bend the center of the binoculars to fit your eyes. The barrels are the two tubular pieces connected to the lenses. Look through the binoculars and grip the barrels by the sides. Then, bend your binoculars up or down at the center, so that both your eyes fit comfortably over the lenses. When you look through the eyepiece, you should see one circular image. If you see a double image or dark circles, then you need to readjust the barrels.

   • The distance between everyone’s eyes differs, so you’ll need to adjust the barrels for your eyes so that the binoculars fit your individual face.
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3. 
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   Focus the left lens with the central focus knob. As Dr. Lederer explains, “To adjust your binoculars to your eyes, close your right eye and focus your left eye on a distant object using the central focus.” The central focusing ring or knob is the wheel in the center of your binoculars, between the barrels. Rotate the ring left and right (with your right eye closed!) until the image becomes clear in your left eye.

   • Once the image is sharp in your left eye, you can open your right eye.
4. 
   4
   Focus the right lens with the diopter dial. “Then, close your left eye and use the focusing (diopter) ring on the right eyepiece to focus your right eye,” says Dr. Lederer. Since most people have slightly different vision in each eye, he explains that the diopter dial “compensates for the difference in the strength of your eyes.” Rotate the diopter until you can see the object clearly with your right eye while the left lens is still covered.

   • If the vision in both of your eyes is the same, then you might not have to adjust the diopter on the right eyepiece.
   • Focusing on one eye at a time will make calibrating your binoculars easier.
   • Note that simple, inexpensive binoculars may not have a separate diopter ring. In this case, just use the central focus knob to get the clearest view possible when both eyes are open.
5. 
   5
   Look through the binoculars with both eyes open to test your view. The binoculars should feel comfortable, and your test object should be in focus. Most binoculars come with markings on the diopter and central focus dials, so take note of where both are so you know where to adjust them if they get changed or someone else uses your binoculars.

   • Once you get the correct calibration, you shouldn’t have to change it again.
   • If the image is still blurry, you may need to adjust the central focus knob slightly again.
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Section 2 of 4:

How often should you adjust binoculars?

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1. 
   Refocus your binoculars after someone else uses them or you put on glasses. If you’re the only person using your binoculars and the focus knobs tend to stay in place when you put them away, you probably won’t have to refocus them very often (and when you do, you’ll likely only need small adjustments). However, if someone else uses your binoculars, you’ll have to readjust everything—from the eyepieces and cups to the fit of the barrels to the focus knobs—to suit your individual face and eyesight.

   • You’ll also have to readjust your eyepieces and eyecups if you put on glasses when you typically don’t use them (or vice versa).

Section 3 of 4:

What do the numbers on binoculars mean?

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1. 
   1
   The numbers on the barrel indicate the magnification and lens aperture. All binoculars should come with a numerical marking like “10x50” or “7x35” on one of the barrels. The first number indicates the magnification power of the lenses (for example, a 10 would mean objects appear 10 times bigger), and the second number shows the aperture (opening width) of the lenses in millimeters (for example, a 50 would mean the lenses are 50mm wide).

   • Which binoculars are best for birdwatching? “The best choices are sizes 8x42 or 7x35, but try before you buy,” says Dr. Lederer.
2. 
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   Other numbers show the size and distance of your field of view. Some binoculars have an additional set of numbers describing how wide your field of view is at a given distance. For example, you might see something like “80m at 1,000m” or “488ft/1,000yds.” The first number indicates the width of your field of view (in these examples, 80 meters wide or 488 feet wide), and the second number indicates how far away that field of view is (for example, 1,000 meters or 1,000 yards away).
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Section 4 of 4:

How to Clean Binocular Lenses

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1. 
   Remove loose dust with a lens cleaning pen, then wipe clean with a microfiber cloth. Dirty lenses can make even the most well-focused binoculars hard to see through, so keeping them clean is a must! First, use a lens cleaning pen to remove loose dust and debris from each lens (it helps to hold the binoculars upside down while you do this). These pens are soft and specially designed for optical lenses to avoid damage.

   • If there is some stubborn dust on the lenses, moisten a cotton swab with water or lens cleaning fluid designed for cameras and optics (not the kind for glasses) and gently wipe it away.
   • Finish up by wiping the lenses with a soft, microfiber lens cloth to remove any remaining dust, droplets, or residue.

Community Q&A

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• Question

  Are there binoculars I don't have to adjust, that are always right?

  

  Community Answer

  The reason you have to adjust is due to the object's distance that you are looking at. There are specific binoculars that don't require main focus adjustment but they are used for viewing objects far away. However, they say that if you adjust to see an object about a football field away that should be the permanent focus for the diopter adjustment.

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• Question

  What if there is double vision from the binoculars? It appears as if the left and right lenses are not calibrated to give one image. How do I adjust for this?

  

  Community Answer

  Make sure that your binoculars are adjusted correctly for the space of your eyes. If the hinge distance is too wide or too narrow for your eyes, then it is possible that this is what is causing your problem. However, it could be an internal lens issue that would need to be taken to a specialty place.

  Thanks! We're glad this was helpful.
  Thank you for your feedback.
  If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow

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