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.