Adjust your binoculars correctly by setting up their eye relief, width and diopter adjustment.
Binoculars are a wonderful tool for giving us a clear, close view of wildlife. Here in Scotland, for example, binoculars are essential for identifying birds of prey, whales, dolphins and, in some situations, dragonflies and butterflies. However, they need setting up correctly for the best performance. Read on for detailed instructions, or for an overview of wildlife in Scotland, read Wildlife in Scotland: A Beginner’s Guide.
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Adjust your binoculars for the best image
Correctly adjusted binoculars are an essential item on your birdwatching kit list. Why is this adjustment so important? Mainly because without it, the image quality will suffer, leading to missed sightings. You might even give yourself eye strain! You will need to make several adjustments to achieve a clear, bright image. First, the ‘eye relief’, then the width and finally the diopter adjustment. Novice birdwatchers quickly learn to use the main focus, but often overlook the other three adjustments.
For the best performance, buy a decent-sized set of binoculars from a reputable dealer. In terms of size, 8 x 42 size offers the optimum balance of brightness, magnification and field of view. Viking Optical Centres are highly recommended optics dealers in the UK.
Time needed: 5 minutes
How to adjust your binoculars (for models with diopter setting on LEFT eyepiece)
- Remove any protective lens covers
- Adjust the eye relief cups to fit
- Adjust the width to fit
- Close left eye, obtain sharp image through right eyepiece
- Close right eye, obtain sharp image through left eyepiece
ONLY use the diopter setting to achieve this step.
- Open both eyes and check the focus
Eye relief
This first adjustment ensures your eyes are the right distance from the eyepieces. If you wear glasses, rotate, fold or push down the adjustable eyecups. If you don’t wear glasses (or don’t plan to wear them when using your binos), then leave the eyecups in their ‘up’ position.
Adjust binocular width
Next, look through the eyepieces and gently push or pull the two sides together or apart until you can see a clear, circular image. Dark semicircles or a double image usually means the width needs adjusting.
⚠️ Never look directly at the sun with binoculars, even on an overcast day. There is a good chance you will suffer eye damage and perhaps even permanent blindness.
Diopter setting
Now turn the main focus wheel until the image is as sharp as you can make it. It helps to look at something with good contrast, for example a street sign or tree branches against the sky. Next check where the diopter setting is located: either on the left eyepiece or on the main focus wheel.
In most binoculars, the diopter adjustment is on one of the eyepieces (usually left). If it is on the main focus wheel, you will need to unlock and adjust it there, instead of on the eyepiece.
Looking through the binoculars as before, close the eye that has the diopter adjustment (usually left). Keep looking with the other eye and use the main focus wheel to get a sharp image. Now open the eye with the diopter adjustment and close the other eye. This time obtain a sharp image by adjusting the binocular diopter ring. Lastly, look through the binoculars with both eyes and you should see a single clear, sharp image. If you feel more fine tuning is needed, adjust the binocular diopter setting again.
Binoculars are an essential tool for watching wildlife in the field, and you will get the most out of them if they are set up specifically for your eyes. Once the diopter adjustment is done, you can leave that alone, unless you lend them to someone else.
Spring birding in the Cairngorms and more
The diopter adjustment is a small focus mechanism on binoculars that lets you set a slightly different focus for each eye. Most people have one eye that is slightly stronger than the other and this setting helps them to achieve a crisp, clear image.