Those who spend a lot of time outdoors know just how essential a good pair of binoculars is, especially when it comes to viewing something at a distance. More importantly, those who frequent outdoor activities know how important it is to focus the image you see when using your binoculars. Therefore, it is important to get familiar with both the focus wheel and the diopter on a binocular.
While many people know how to use a standard focus wheel, properly setting the diopter on a binocular is still a grey area. Simply adjusting the focus wheel located between the viewing barrels can help, because they focus both barrels at the same time. The diopter takes this process a step further and corrects the differences in the focus points between the two barrels, compensating for different eye strengths.
Being able to adjust our focus and home in on our target is wonderful when you are out on the hunt or looking for a bird. What’s more, by adjusting both the focus wheel and diopter, we’re not only getting a clearer image, we are avoiding troublesome issues, including eye fatigue and headaches. Knowing how to correct the focus of our binoculars is essential, and while many understand how to use the focus wheel, we need to understand what the diopter is and how to adjust it.
What is a Diopter on Binoculars?
A diopter measures the refractive power of lenses. It is typically measured in millimeters and the higher the diopter, the stronger the lens and the larger the correction that will be needed to focus our image.
That said, the diopter is used to help focus the image that we see once we look through the lens. Some people confuse the diopter with the focus wheel. While they both help adjust the focus of our image, the do so in two very different ways. When it comes to adjustable diopters on binoculars, there are two types:central focusing and individual focusing.
Central Focusing Binoculars
Central focusing binoculars have a single focus knob or diopter. These binoculars are considered the most basic for any outdoor needs and make use of a central focusing knob and a single adjustable diopter traditionally located on the right eyepiece and indicated by a diopter range, which is marked similarly to, “-0+”
The center focus knob helps to focus both the left and right eyepieces at the same time. The diopter than goes a step further and allows us to focus each individual eye to compensate for different eye strengths.
Individual Focusing Binoculars
Individual focusing binoculars are also known as binoculars that have independent diopter adjustment, which allow us to focus each eye individually. Aside from not having a traditional focus knob located between the two barrels, these binoculars make use of focusing rings on each barrel, allowing for a significantly more precise image. We can then use the diopter lock to lock them in place, so they are ready for use at a moment’s notice.
How to Focus Binoculars with a Diopter in 3 Steps
Our team member, Matt Rice, visited Babes with Bullets to explain how to adjust binocular diopter for optimal use and stated that each person needs to adjust not only the focus knob but also the right and left diopter located in each eye cup on certain sets of binoculars.
When it comes to learning how diopter adjustment works and addressing the frequently asked question “how to set diopter,” using a set of central focusing binoculars, Matt explains that it only takes 3 steps to focus the diopter on a binocular:
1. If our diopter is located on the right barrel, then we begin by looking through the left barrel with our right eye close. Start by adjusting the center focus knob/diopter until the image is as crisp as we can get it.
2. When we’re ready to adjust the right eye, we’ll go ahead and close our left eye, and adjust the diopter on the right barrel until our image is as, again, as crisp as we can get it. Once we are happy, we can use the diopter lock to lock it in place.
3. Finally, we’ll go ahead and open both our eyes and using the center focus knob, fine-tune the image that we see until it is perfect.
If we need additional help with eyecup and interpupillary distance adjustment prior to focusing our binoculars, we’ll go ahead and reference our binocular instruction manual.
Can You See Me Now?
Binoculars are the world’s most used optical instrument, besides eyeglasses. Since their sole purpose is to help us see our target at a distance, we want to make sure we see the most precise image possible. When the diopter lens is left unadjusted, the picture quality will not be optimized, which can lead to eye fatigue and even headaches.Therefore, learning how to focus binoculars with a diopter is essential, no matter what outdoor activity we are partaking in.
Luckily, Bushnell not only has a wide variety of binoculars to choose from, but each pair also comes with a useful quick start guide to help us quickly adjust our diopter to maximize our binocular’s image capabilities. If that quick start guide isn’t enough, then there is always the full manual which is available online for quick access.
With over 70 years of experience, Bushnell has binoculars both with and without diopter lenses. Whether you have an idea of what you’re looking for or you need help choosing the right set of binoculars for your outdoor activity, you can find your perfect pair of binoculars by using our binocular finder today!