You can’t just pick up a pair of binoculars and start looking through them. You’ll likely see images that are out of focus, images will be out of alignment and you’ll experience eye fatigue. So how to set up binoculars?
To get the best out of binoculars, it is important to set them up properly. This is especially important when they are new or if someone else was using them.
Setting up binoculars, whether for terrestrial or celestial observations, takes a few minutes. It involves adjusting the eyecup, setting the right interpupillary distance and making sure both eyepieces are in focus.
1. Adjust the Eyecups
Eyecups are the two parts that rest against your eyes when you are looking through the binoculars.
If you don’t wear glasses, you should turn them up until they are fully extended. This ensures your eyes are a comfortable distance from the eyepiece lens.
If you wear glasses, set the eyecups to their lowest position. If they are foldable rubber eyecups, fold them down such that eyepiece lens is closer to your eye. This ensure you experience the full field of view.
2. Adjust Eye Width
The distance between your eyes is called interpupillary distance. Most binoculars allow you to adjust the distance between the two tubes so that the eyepieces fit your eye width perfectly.
To check if the interpupillary distance is set properly, look through the binoculars. If you see two circles overlapping each other, you need to adjust the eye width. Using the binoculars like this will quickly tire your eyes.
The two tubes are in alignment with your eyes when you are able to see a clear non-overlapping view.
3. Adjust Focus (Focus Ring and Dioptre Adjustment)
Next, you need to adjust the focus of both lenses. By the way, have you cleaned them?
Go outside (during the day) and look at an object about 50 metres away through the binoculars. The object will likely appear blurry.
Close your right eye or cover the objective lens on the right. Look at the object using your left eye only and adjust the focusing ring until the object appears sharp with no blurriness.
Next, close your left eye (or cover the left lens) and look at the same object using your right eye only.
Because each eye is slightly different, an object that was in focus when looking through your left eye may now appear blurry to your right eye. Normally, these differences in sight are unnoticeable because the brain smooths over the views delivered by both eyes.
But because of the high magnification of binoculars, they differences become apparent.
Don’t touch the focusing ring to focus the image for the right eye. That will mess focus for the left eye. Instead, use the dioptre adjustment ring that’s located on the right tube of the binoculars.
Keeping your left eye shut, turn the dioptre ring left or right until the object appears sharp.
Now open both eyes. The object should appear sharp to both eyes.
After this, there’s no need to adjust the dioptre ring. You’ll be adjusting only the focusing ring to observe objects at varying distances.
But if someone uses your binoculars, you may need to re-adjust the dioptre for your eyesight. Some people also find they need to adjust the dioptre when switching from daytime (terrestrial) observations to night-time (celestial) observations.
Note: The above instructions are for central focusing (CF) binoculars. If your binoculars have an individual focusing ring on each tube, adjust focus for each eye in turn, while keeping the other shut.
4. Hold the Binoculars the Right Way
When looking through binoculars, it is important to reduce arm movements. Any shakiness will be highly apparent because of the magnification.
Hold your elbows against your body and wrap your hands firmly (but not too hard) around the tubes of the binoculars.
If you plan to stargaze for long periods, consider buying a tripod to reduce arm fatigue, and possibly also image stabilising binoculars. Here’s my article on summer stargazing with binoculars.