Your eyes are probably not the same!

Many people mightn't realise they have a slight difference in the focusing of their left and right eyes. It's something that's quite common and a diopter adjustment allows you to adjust for this variation between your eyes. It means that the binoculars have a different focus. 

Binoculars usually have a small dial or ring that allows you to make a diopter adjustment. 

How do I adjust the diopter?

We tell people to close their right eye and look through your binoculars. (If this is tricky, put on just the right eyecup) then using just your left eye, focus your binoculars on something a little bit in the distance that has some crisp detail. This could be a tree branch, a rooftop or a traffic sign.

Now, reverse the process. Shut your left eye or cover the left lens of your binoculars.

This time don't touch the central focus wheel. Instead, adjust the diopter dial.

This could be a dial around the outside of the right eyepiece such as the one on these Nikon Monarch M7 binoculars. 

Depending on your binoculars, you just need to firmly twist them. On others, you might need to click up the right ring and then click it back down when you've finished the adjustment. 

These Leica Trinovid binoculars at BINTEL use a click ring around the focuser to adjust the diopter.

Twist the ring slowly from left to right to see if the image in your right eye comes more sharply into focus.  Hopefully it won't need much movement away from the central position at all!

Next, switch eyes. Cover the left objective lens or close your left eye and now look only through the right side. This time do not touch the central focus wheel. Instead, turn the diopter ring until the same object is sharp for your right eye.

Open both eyes or remove the left lens cap. You should notice that the view through your binoculars is a little sharper, especially if you need to twist the diopter dial more than a small amount.  The slight difference in your eyes has been "dialled" into your binos. 

It might be worth repeating the process a couple of times focussing on different objects in the distance to fine tune the process.

It's probably a good idea to make note of the diopter setting in case it gets bumped or you need to share your binos with other people. 

What about if I wear glasses for long distance viewing and I want to use them with binoculars?

If you use glasses for distance viewing, your optometrist has already taken into account the difference between your eyes as part of your glasses prescription. 

You should be able to use your glasses with binoculars without the need to adjust the diopter setting.  The only thing to make sure of is that your binoculars have a decent eye relief. Eye relief is the distance behind the eyepiece at which your eye still sees the full field of view. Because your glasses hold the binoculars further from your eyes, you need longer eye relief to still see the whole image. Generally speaking, 15mm or more is comfortable for glasses wearers.

What about if I wear glasses for long distance viewing and I don't want to use them with binoculars?

In this case, there's a good chance you'll be able to use the focus to account for the change in focus your glasses perform. If the differences in your left and right eyes are too large for the diopter adjustment in your binoculars to cater for, you will need to still use your glasses. There are also some conditions, such astigmatism, that will still require you to wear your glasses. 

This is only a brief introduction, so have a chat to us at BINTEL for more information!

Cheers,

Earl White

BINTEL

26th June 2026