a matter of focusing on the subject depending on how near or far away it is from you using the main central focussing wheel: If the diopter adjustment ring is on the right barrel, start by shutting your right eye and leaving your left eye open (do the opposite if it is on the left barrel) - If you prefer, you can also just cover the end of the barrel with your hand. If the diopter is located on the central focusing wheel, refer to your manual to establish which barrel it affects, but it is usually the right one. Keeping your eye shut, use the center knob to focus on an object about 8 - 10 meters away (approx 30ft) until it becomes sharp. Open your right eye. Next, shut your left eye and leave your right eye open Now look at the same object and turn the diopter ring until you are also clearly focused on it. Look through the binoculars with both eyes open, and you should have a clear, crisp view of the object. Done! The binoculars are now correctly calibrated for your vision. Diopters located in front of the Central Focussing Wheel Diopter Adjustment on the Focussing Wheel Some binoculars have the diopter adjustment located in front of the central focussing wheel. To adjust the setting, you first you focus your binoculars on something as normal, but with only one eye open (usually your left), keeping the other shut. Then you swap eyes, look through