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How can I adjust my binoculars so I don’t see blacked-out areas?

A small beige and brown bird with orange patches and a bright blue throat, stands with its tail upright.
If you see two circles when you look through your binoculars, use the central hinge to move the barrels closer together. The goal is to see a single clear circular image. Bluethroat by Bryan Calk/Macaulay Library.

Considering how expensive binoculars can be, it’s odd that most companies don’t include operating instructions in the package. Using binoculars is like riding a bike—easy once you get the hang of it.

Virtually all binoculars have several helpful features that allow them to be tailored to different users. This means that before you try to see birds through your binoculars, you need to make a few adjustments. Here’s how:

Adjust the Eyecups

The eyecups hold the ocular lenses (the lenses you look through) exactly the right distance from your eyes (this distance is called eye relief), to optimize magnification and cut out peripheral light, making the image clearer and brighter. Extend the eyecups if you don’t wear eyeglasses. Most eyecups have a few preset distances to choose from, to match the shape of your eyes and how you hold your binoculars. Since eyeglasses hold binoculars away from the eyes and let in peripheral light anyway, eyeglass wearers will want to fully retract the eyecups.

Adjust the Barrels

Next, set the barrels of the binoculars to match the distance between your eyes. Looking through them, adjust the barrels until you have a single image through both eyes. If the width isn’t set properly, your image will have blacked-out areas in the middle or at the edges.

Adjust the Diopter

Virtually all binoculars use a single center focus knob that controls the focus for both eyepieces simultaneously. But because most people’s eyes aren’t precisely matched, binoculars also have a separate dial called a diopter adjustment that compensates for the difference between your eyes. (Note that for people who wear corrective lenses, the correction will likely minimize the difference between your eyes and make the diopter adjustment less critical.) The diopter adjustment is usually below the right eyecup or on the center hinge of your binoculars and normally numbered from +2 to –2. You should only need to set the diopter once. Here’s how to adjust the diopter so you can use your binoculars without eyestrain:

Show Transcript
[fun upbeat music and clapping percussion]One of the great joys of birding is seeing birds clearly through binoculars. Here are a few tips how to set them up and a couple of ways to use them.[music ends]
If you are picking up binoculars for the first time, there are a couple things you might want to think about before you even look at a bird.
First, check to make sure that the distance between the barrels lines up with your eyes. You’re shooting for one circular image when you look through the lenses.  
Next, take a look at the eyecups…If you are wearing glasses, you’ll want the eyecups rolled down. If you don’t wear glasses, keep them rolled up.  
One last thing that can cause trouble is the diopter. It’s a feature to help compensate for the differences between your eyes, but if it’s not set correctly you’re not going to get the clear view you are looking for. Find the diopter adjustment, usually near the right eyecup—you can either make sure it’s in the center, or set it for your eyes. Set the diopter by covering the right eye and turning the focus wheel so that your left eye is focused on a fixed object. Make sure it’s nice and sharp. Then cover your left eye and look at the same object thru the right eye. If it’s not sharp adjust the right eye diopter accordingly. And you’re set!
From that point forward you will not need to make this adjustment again, but make note of where you set it in case it gets moved out of place. [Musical transition]
When you spot a bird, keep looking at it and lift the binoculars to your eyes. [music fades out] Then turn the focus wheel until the image becomes clear. It’s not a bad idea to practice this a few times even if you aren’t looking at a bird.
Scanning is another great way to find birds. Even if you don’t already see a bird you can use your binoculars to help. Let’s say you are searching a lake for water birds. Lift your binoculars and focus them on the horizon or the far side of the lake. Then slowly pan across the landscape. But be ready for the unexpected bird to pop up…you want to be able to dial that focus in quickly and enjoy the view.
A good pair of binoculars is your most important tool for spotting birds…so find a pair you like and take them with you on your next adventure.[music starts and plays to end] 

End of Transcript

More on Binoculars

  1. First find the diopter adjustment and set it at zero.
  2. Find something a good distance away that has clean lines. A sign or something else with letters or numbers is often a good choice.
  3. Cover the objective lens (the large outside lens of the binoculars) with the lens cap or your hand on the side controlled by the diopter adjustment, and then focus on the sign using the center focus knob. Try to keep both eyes open as you do this.
  4. Switch hands, uncovering the lens with the diopter adjustment and covering the other lens. Focus again, this time using the diopter adjustment, not the center focus.
  5. Repeat a couple of times to make sure. After you’re done, your sign should be crisply focused through both eyes.
  6. Notice the number setting on the diopter adjustment. Sometimes during normal use, the adjustment knob may get shifted, so every now and then when you start using them, check to make sure it’s set where it should be for your eyes.

Adjust the Neck Strap

Finally, make sure the neck strap is comfortable. Many people like the strap as short as it can be while still allowing you to put it over your head easily. This minimizes how much the binoculars will bounce against your chest or swing out and hit rocks, tables, or other objects whenever you bend down. Some birders like a little extra length so they can tuck the binoculars under one arm as a way of cutting down bounce. And many birders trade out their single neck strap for a binocular harness that takes some of the weight off your neck and holds the bins more securely to your chest.

If you’re new to birding, watch our free how-to video series, Inside Birding, to get started on identifying birds with confidence.

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American Kestrel by Blair Dudeck / Macaulay Library