What Is A Diopter On Binoculars & How To Adjust Them - Our Guide

Written by 

Steven 

Updated on: 

October 12, 2021

Our Guide To Adjusting The Diopter On Your Binoculars

Buying the best pair of binoculars is a great start to getting the best image quality out of your optics, but not knowing how to set the focus and dioptre of your binoculars can produce a blurry image and limit your observation. 

The diopter adjustment on your binoculars refers to the refractive power of the lens, the higher the mm of the diopter than the stronger the lens on your binocular diopter and the more correction it will need. 

To adjust the central diopter on your binocular you have to shut either eye and adjust the image until clear, this will be different if you have a central focus system on your binoculars. 

We will cover more about the difference between the central focusing mechanism and dioptre focusing systems on binoculars below, how to perform the diopter adjustment on your binoculars as well as some troubleshooting tips if your image is still blurry after diopter correction. 

What Is Diopter Adjustment? 

So as we can understand how to set adjustable diopters, we have to understand what this part of your binoculars does first. The diopter adjustment knob on your binoculars is a one-off adjustment that allows you to calibrate each eyepiece of your binos individually for a more fine-tuned precise image. 

 The diopter adjustment barrel is typically located on the right eyepieces of most binoculars and is set up at the beginning when you buy your binos. 

What Is Central Focus Adjustment?

More people are familiar with the central focus adjustment on their binoculars which is located in the middle of their binoculars, this makes your image focus when turned, some of the cheaper binoculars only have a central focus wheel without a diopter but do not give the same level of vision correction as individual diopter adjustment does.

How To Perform Diopter Adjustment On Your Binoculars 

Using the diopter adjustment knob on your binoculars is a simple process and can make a big difference for image clarity and vision correction when set properly. 

We will cover how to use the diopter adjustment setting on common binoculars below but it does differ according to the pair of optics you are using, if you get stuck always double-check your binos manual. 

  • Step one - First of all, find the diopter adjustment knob on your binos, this will likely be on the right eyepiece, make sure you set the diopter adjustment knob to zero before we start focusing.
  • Step two - Close the eye that your diopter lens is on and look through the other eye, choose an object around 30 feet away then move the central focus wheel until you see a crisp image, choosing an unmoving object will work best for this task.
  • Step three - Now close the other eye and turn the diopter adjustment wheel till you see a clearer image again. 
  • Step four - After adjusting the diopter gearing you can now check your vision in both eyes and adjust the central focus wheel until you get the perfect focus image, repeat steps until achieved. 
  • Step five - Now everything is set you can use the diopter lock to keep everything in place, if your binos do not have this then you can mark it with a chalk line to remember when the optimal place is.

Tips For Fixing a Blurry Image On Your Binoculars 

Even after setting your focus and diopter adjustment you might still be seeing a blurry image through your binoculars, we have put together some common troubleshooting reasons as to why this might be happening down below to help you find a solution.

  • Check the eyecups - If you do not wear glasses then you should ensure the eyecups on your binoculars are twisted up out of the way, for eyeglass wearers they need to be set at the shortest difference to make sure they are not limiting your vision.
  • Make sure your binoculars are clean - Smudges and debris can build up on your binoculars lenses if you are not careful, causing a blurry image. To clean your binos properly you must never use a t-shirt, always use a proper lens cleaning solution and a microfibre cloth as well as some compressed air to get rid of any dust.
  • Check the distance between your barrels - Make sure that the barrels of your binos are aligned properly with your eyes at a proper distance, some binos automatically fold back.
  • Evaluate your distance to your subject - If your close focus range is limited then your subject might be too close, hence why it looks blurry, same goes for when your subject is too far away, your magnification might be too limited. 
  • Look at your prescription - It could be possible that your eyesight has changed, this can happen with age, always readjust the diopter and focus on your binos when your eyeglass or contact lenses prescription changes. 
  • Consider light conditions - When viewing subjects through your binos varying weather conditions such as fog and shadows can cause your image to look blurry through the lens even when it is set right.

Frequently Asked Questions About Binocular Diopter & Adjustment 

Do roof prism binoculars have diopter adjustment? 

Yes, roof prism and Porro prism binoculars both have diopter adjustment, some of the more advanced optics might have this on the left barrel with a diopter lock.

Where is the diopter range on my binoculars?

The diopter range is typically on the right side of your binoculars but can sometimes be in the centre too, your binos manual will always say where if you are unsure.

Is the diopter helpful for a sharp image on my binoculars? 

Yes, the diopter is very important for the best quality image as it calibrates both of your eyes individual differences. 

When should I change my diopter adjustment? 

The diopter on your binoculars is always changed when your first get your binos but only has to be changed again if your eyesight changes or someone else is using your binoculars.

Final Words  

To conclude, setting the binocular diopter is important if you want to get the most out of your binoculars, not only for proper focus but also for correcting the difference in your vision between each eye.

Some binoculars might have an all in one central focusing knob or no diopter adjustment at all depending on the quality of the binoculars, always refer to your manual for the proper settings if needed.

Born and raised in the south coast of UK, a small town close to Cornwall, I have adventure in my blood. Ever since a young age, I have always been into the great outdoors and particularly love watching the natural wildlife. Birdwatching is what I enjoy the most, and thus my natural interest in binoculars began. I founded and run Best-Binoculars.UK a site where I talk about various aspects of and review binoculars. Hope you enjoy my ramblings :)

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Steven
Born and raised in the south coast of UK, a small town close to Cornwall, I have adventure in my blood. Ever since a young age, I have always been into the great outdoors and particularly love watching the natural wildlife. Birdwatching is what I enjoy the most, and thus my natural interest in binoculars began. I founded and run Best-Binoculars.UK a site where I talk about various aspects of and review binoculars. Hope you enjoy my ramblings :)

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