Just about everyone can figure out how to focus their binoculars, using the central focusing wheel that moves the optics on both barrels simultaneously.

What many people don’t realize, though, is that there is another step required to making sure you get the clearest, sharpest image possible. This step is properly calibrating your binoculars for your vision.

The reality of our eyes

A large portion of people have one eye that is stronger than the other. This eye is usually the dominant eye, and you don’t realize the difference in strength between your eyes simply because your brain automatically focuses them independently to give you a sharp, clear view. With a pair of binoculars, though, your brain doesn’t know how to adjust the focus. If you don’t properly calibrate your binoculars for your vision, you’ll never get a completely sharp image, and you’ll assume the optics are faulty.

Diopter adjustment

In addition to the focusing wheel, most binoculars also include a diopter adjustment ring. You’ll know the diopter adjustment wheel, because it will normally be marked with something like the following: – 0 +

This mechanism adjusts the focus on one barrel independently of the other, and is used to compensate for any differences that might exist between your left and right eye. This diopter adjustment ring is usually located on either the left or right barrel of the bins, but might also be located in front of, behind, or integrated into the main focusing wheel.

How to calibrate your binoculars using diopter adjustment rings on the barrel

This process usually only needs to be done once, unless you inadvertently change the setting or someone else with different vision from yours uses your binoculars. Once this is done, you should be able to focus on your subject and get a completely sharp, crisp image.

1. If the diopter adjustment ring is on the right barrel, start off by looking through the binoculars with your left eye open and your right eye closed. If the ring is on the left barrel, do just the opposite.
2. Keeping your eye shut, use the focusing wheel to focus on an object approximately 30 feet away until it becomes sharp.
3. Open the eye that was closed, and shut the other eye.
4. Look at the same object, and turn the diopter ring until the subject is clearly focused.
5. Now, open both eyes and look through the binoculars at the same object. It should be clear and crisp, which means your binoculars are now calibrated for your vision!

Diopter adjustment rings in other places

If the diopter adjustment ring isn’t located on the barrel, the above procedure still remains the same. You just have to look for the adjustment somewhere else, and your owner’s manual will tell you for sure where that is.

Sometimes, the diopter adjustment will be located on the front of the central focusing wheel. Following the above procedure, you focus on an object with one eye closed, then swap eyes and turn the diopter adjustment wheel in front of the focusing wheel until the opened eye is perfectly focused on the same object.

Some binoculars, like the very high end Swarovski EL line of binoculars, have the diopter adjustment setting integrated into the focusing wheel. To adjust the setting on these, you pull back on the focusing wheel to engage the gearing on the diopter and reveal the graduated scale. Then you turn the wheel as you would during normal focusing, but this time the wheel adjust the diopter setting instead. Once you’ve got the diopter perfectly adjusted, you click the focusing wheel back into place to lock your setting.

Don’t settle for less than the best

There are a few models of inexpensive binoculars that don’t have diopter adjustment mechanism at all. Don’t settle for these cheap bins, because you’ll never get a perfectly sharp image out of them. Even if you assume your eyes are the same, you’ll always find some amount of difference between your left and right eye. Most of the time when people get frustrated with trying to look through binoculars, it’s because they don’t have the diopter properly calibrated, so make sure you can perform this crucial step to getting the best possible view out of your binoculars.