Most high quality binoculars have what is called a dioptre adjustment. People’s left and right eyes rarely have the same strength or focus, the diopter setting is to compensate for this difference.
Most commonly it’s found as a ring adjustment on the right hand eye piece although as you can see mine is on the left. Have a read of your owner’s manual to locate where this adjustment is on your particular bino’s.
Not having this adjusted correctly can cause eye fatigue and possibly even headaches as your eyes will be straining to focus. It’s simple and quick to set up correctly and it will make a real difference to how long you can comfortably glass.
The adjustment process
Pick out something about 100 metres away that has a lot of detail but that is easy to see. For example, a dark rock against a blue sky.
First set the centre focus to your eye that doesn’t have the diopter setting. So let’s say your adjustment dial is on the right hand tube, we are going to cover the right lens then roll the centre focus until will have an image that’s as crisp as possible.
Tip: Use a dark piece of paper or card and get someone to hold it over the right lens for you; if you’re by yourself then you can just close your right eye.
Now cover the left lens and adjust the diopter ring to again find that perfect focus. Be careful not to change the centre focus in the process.
Tip: Some bino’s will have a locking mechanism to keep the diopter at the same setting, others will have markings. I tend to make a mark on the dioptre with a permanent marker, this way I know exactly where it needs to be if the setting gets bumped or adjusted for someone else.
So as you can see (no pun intended), the diopter setting is worth getting right. The adjustment process is quick and simple, and your eyes will thank-you for it.