Summarized from The Cornell Laboratory of Ornithology’s All About Birds instructions for how to adjust your binoculars.
You’ll certainly enjoy birdwatching more if you can see the birds clearly through your binoculars. To make sure you’re getting a big, bright, crisp picture through yours, you will want to make sure they are adjusted correctly.
Start by making the neck strap as short as it can be. You should still be able to use the binoculars comfortably and put them over your head easily. The longer the strap is, the more the binoculars will bounce, and the greater the chance you may bonk them against something.
Then, adjust the eyecups. Extend the eyecups if you don’t wear eyeglasses. Because eyeglasses hold binoculars away from the eyes and let in peripheral light anyway, retract the eyecups if you do wear glasses.
Next, set the barrels of the binoculars to match the distance between your eyes. Looking through them, adjust the barrels until you have a good image for both eyes. If the width isn’t right, your image will black out.
Use the diopter adjustment to focus both eyes. Our eyes are seldom precisely matched, so to accommodate the difference, binoculars have a diopter adjustment near the optical lens on one side or the other, or as part of the center focus knob. Diopter adjustments are normally numbered from +2 to –2. Here’s how to adjust the diopter so you can minimize eyestrain:
Find the diopter adjustment and set it to zero.
Find something a good distance away that has clean lines. A sign or something else with letters or numbers is often a good choice.
Cover the objective lens (the large front lens) on the side controlled by the diopter adjustment, and then focus on the object using the center focus knob. Try to keep both eyes open as you do this.
Uncover the lens with the diopter adjustment and cover the objective lens on the other side. Focus again, this time using the diopter adjustment, not the center focus.
Repeat a couple of times to ensure that you have the best view. Your object should be crisply focused through both eyes.
Notice the number setting on the diopter adjustment. Sometimes during normal use, the adjustment knob may move, so every now and then, check to make sure it’s set where it should be for your eyes.
Once you have the diopter adjustment correct you can control the focus for both eyepieces simultaneously using the center focus knob.
If you still can't figure it out, just ask one of the staff members at Quest and they will be happy to help you adjust your binoculars. If you don't have binoculars, you can borrow some at the front desk for your hike at Latta Nature Preserve.
If you would like a beginner course on identifying the birds you see through your binoculars, check out this free offering on Cornell’s All About Birds website.
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