Binoculars consist of two parallel telescopes, hence the name “binocular” which refers to “binocular vision” which means “seeing with two eyes”.
So that you can see really well with both eyes at the same time through the two binocular tubes, both optics must be well adjusted to your eyesight. Only then do the images overlap well and become one sharp image.
Unfortunately, many people do not have the same eyesight in both eyes and see differently sharp. The eyes have different refractive power (diopters). Even the best binoculars require the user to adjust the diopter compensation correctly, only then can you enjoy good, fatigue-free vision with the binoculars over a longer period of time.
Precisely for this reason, binoculars have a diopter fine adjustment on an eyepiece with which one can correct the different eyesight. With its help, the different refractive powers of the eyes can be compensated.
Why Diopter adjustment
Most people are not even aware of their eyes slightly different eyesight until they look through binoculars for the first time. This is because the brain has the ability to correct only slight differences in the refractive power of the eyes without us being aware of it.
During brief observation through binoculars, provided the different eyesight is only weak then the brain will also compensate for this difference. However, if you look through binoculars for a long time, this strain can lead to eye fatigue or headaches.
With the binocular diopter adjustment, you can compensate for any deviations in the eyesight. The adjustment is mostly located on the right eyepiece and allows fine focusing of this particular eyepiece.
How To Adjust Binocular Diopter
Binoculars have two focus adjustment options so that the observed object can be shown perfectly sharp.
One is the central focus wheel. It is, as the name suggests located in the middle, usually as a large, easy-to-use adjustment wheel, between the two barrels. Turning it moves both eyepieces simultaneously either inwards or outwards.
The other is the diopter compensation which can be found in at least one of the two binocular eyepieces, one speaks of a so-called single eyepiece compensation.
In order to see an object sharply with both eyes, the binoculars must be adjusted to the visual strength of both eyes.
Proceed as follows:
- Choose an object at a suitable distance and close your right eye
- Now use the central focus wheel to bring your left eye into focus
- Then close your left eye and focus your right eye with the diopter adjustment
- If you now open and close both eyes alternately, the image should be sharp for both eyes
- Once the diopter compensation is properly adjusted for your eyesight, all you have to do is use the center focus wheel to refocus when viewing objects at different distances.
What is the maximum Diopter Adjustment?
The exact adjustment range of the fine diopter adjustment can normally be found in the datasheet of the particular model. On the datasheet are also all other important specs. Most standard binoculars have a dioptric compensation between +3 and -3 dioptres. However, there are also some models among the premium binoculars that have a diopter correction of up to +/- 8 DPT. At the other end of the scale are the cheap binoculars, which often do not give precise values of how high the diopter compensation is, but simply have a +/- on the eyepiece. You can read more about diopter adjustment here.
In the case of significantly greater visual differences between the eyes, the glasses must be worn to compensate. Then you should definitely buy binoculars that are equipped with special eyepieces for people who wear glasses.