What Is Diopter Adjustment In Binoculars

What Is Diopter Adjustment In Binoculars?

The diopter is the measure of the lens optical power, and it’s determined using focal length. The higher you have to adjust the diopter, the stronger the lens needs to be. Our eyes are individual and unique, and we often don’t realise we have a slight problem with focussing one lens until the headaches start. 

Binoculars have two lenses, one for each eye and it’s not until we use the binoculars that we notice that there’s a difference between them. This is because the brain tries to compensate between each eye and compensate for the difference. Because the binoculars have two lenses which means we are looking through two different lenses, with different magnification on each eye.

Which is when we first notice we have a slight problem, because the magnification exaggerates any differences between our eyes. Most binoculars have one eyepiece that has a mark with +/- marked on it. This is the diopter and it can be focused individually. The diopter is usually on the right eyepiece and is used to focus the eye for ease of viewing.

How To Set The Diopter On Binoculars


Once you’ve located the diopter it’s easy to adjust it to make the images you see through the binoculars clear. 

  1. Locate The Diopter
    Once you’ve found the diopter, set it at zero.
  2. Block The Eye That Has The Diopter
    Cover this lens with the lens cap.
  3. Keeping Both Eyes Open
    With the right lens still covered, focus on an object a way in the distance. Then using the centre focussing ring twist until the object you’re focussing on looks clear through the left eye.
  4. Remove The Lens Cap From The Right Lens
    Then cover the left lens using the lens cap.
  5. Now Adjust The Diopter Ring
    Twist the diopter knob until the same image you focussed on earlier is as clear as you can make it.
  6. Remove The Lens Cap
    Now look through both lenses, the image should be clear, crisp and sharp
  7. You Have Now Successfully Set The Diopter
    You should not have to refocus the right eye with the diopter ever again, unless your eyesight changes. Don’t touch the diopter anymore. Just focus using the central focussing knob.

Central Column Diopter Adjustment

On some binoculars the diopter is on the central column. It works in just the same way and should be adjusted just as we did above, but using the diopter. There are some of the top grade binoculars that have a locking mechanism that prevents the diopter from getting moved accidentally.

Locking Diopters

These locking diopters are usually only found on incredibly expensive binoculars so are not usually applicable when setting an average pair of binoculars. If your binoculars do have a locking mechanism on the diopter it will need to be freed to adjust the diopter setting.

Frequently Asked Questions

Do all binoculars have diopter adjustment?

Some of the cheaper binoculars do not have a diopter but most binoculars made by reputable companies do have the ability to adjust the diopter for clearer viewing.

What is the purpose of the diopter adjustment?

The diopter allows you to adjust the focus on the binoculars to suit your personal eye focus.

What does diopter mean in vision?

The numbers on the diopter show the level of adjustment needed for your eyes. If you move the diopter to -1.00, you have one diopter of nearsightedness.

What does diopter strength mean?

The diopter strength refers to the lenses optical power. Applied to reading glasses. Binoculars etc, the optical power of the human eye averages at 40 diopters this means the ability to focus on an object 1/40 of a meter from the eye.

What is the difference between 3 diopter and 5 diopter?

Any object viewed under a 3 diopter lens will appear 175% larger than normal. Whereas that same object viewed under a 5 diopter lens will appear 225% larger than normal.

What is diopter adjustment control?

The Diopter adjustment control is a knob on binoculars that allows you to adjust the image you see whilst compensating for any differences in your eyes. Usually located on the right lens, the diopter fine tunes the image.