Adjusting new binoculars: how to set up and focus binoculars for bird watching

If your binoculars are lacking any instructions on how to set them up, follow our guide to make sure that you are getting the most out of your new purchase.

Binoculars can be customized to fit the width of your face and to cater to the viewing capacity of your eyes.

Knowing how to do both of these small adjustments will make a big improvement to your comfort and enjoyment as you use the binoculars.

Even if you do have instructions, this guide will explain all the steps in detail, so that you understand how they will improve your viewing experience.

We also cover: how do you fix binoculars that won’t focus? Why are my binoculars blurry on one side?

This guide will also be useful for people who want to know how to focus binoculars, or how to fix binoculars that won’t focus. 

Sometimes people might wonder how to focus binoculars that always seem to be blurry or out of focus. If you have found that simply turning the focus wheel does not bring the image into focus for you it may be that you need to follow these steps below. 

One these steps are followed to set the diopter, it will tailor the binoculars to your vision. One side of your binoculars may be blurry because your vision is different in each eye. 

Adjusting the diopter will address this problem. This will then enable you to focus the binoculars properly using the focus wheel. Read on to find out how.

Getting started: how to set up your binoculars

The first step is to make sure the binoculars are the right width to suit the distance between your eyes.

After that, the eyepieces are in the right position for the next step, which is to adjust the focus using the diopter. This is sometimes also written as ‘dioptre’.

You can do both of these adjustments easily and in a few minutes.

Each of the steps is simple. The instructions look long only because we have included details on why each step is important to help you understand how the binoculars work!

How to set the interpupillary distance on binoculars

1. Remove the lens caps from both ends of the binoculars.
2. Hold the binoculars orientated so that the smaller ends of the tubes are nearest you, and the larger lenses pointing away from you. You will be looking into the smaller lenses, called the ocular lenses.
3. The smaller lens will usually be on an extendable eyepiece. If you wear glasses, leave the eye cups as they are, retracted. If you do not wear glasses, twist the eye cups so that they extend. This lengthens the total length of the binoculars slightly.
4. The two barrels of the binoculars are connected by one or two central pivots. Gently but firmly squeeze or extend these hinges so that the space between the eyepieces matches the space between your eyes. The measurement (in millimeters) between the two centers of your eyes is called the interpupillary distance.
5. To make sure that the interpupillary distance is set correctly, lift the binoculars up to your eyes and look through. Adjust the distance until you see a perfect bright circle. This means that the left and right fields of view are aligned correctly for your particular interpupillary distance. If you begin with two circles, move the barrels so that they merge into one. If you see black areas it means that the width isn’t set correctly.

To learn why it is so important to extend the eye cups, please refer to our article on eye relief.

All about eye relief: choose and use binoculars for glasses wearers

How do I focus my binoculars?

When you move from viewing one object to viewing another object situated at a different distance from you, you may need to alter the focus. The focus ensures that you can see the object clearly without any blurriness.
Different models of binoculars can be designed with three different kinds of focusing mechanism:

• center focus
• individual focus
• fixed focus

In this article, we will cover all these kinds of focus.

Center focus is the most common, so let’s start with that.

Adjust binoculars using center focus

To adjust the focus of your binoculars, you use a focusing wheel. On center-focusing binoculars this is located in the center of the binoculars, between the viewing barrels.

Adjusting the focus wheel will focus both of these barrels simultaneously. But before we can go out and use the binoculars we need to ensure that both sides of the binoculars are adjusted to suit your eyesight, using the diopter.

What is a diopter on binoculars? (dioptre in the UK)

The diopter is the dial on the binoculars that allows you to calibrate each lens separately to suit both of your eyes. In the UK it is spelt ‘dioptre’.

What is the plus + and minus – on binoculars?

It is marked with a + and – sign, usually with a zero in the middle and numbered from +2 to -2.

If it is not numbered, it should have a symbol to indicate the center point, with markings like dots or lines either side of that center point to show the scale.

The sight in each of your eyes may be slightly different. With the diopter, you can make sure that the binoculars are set up to accommodate the viewing range of the left and the right eye.

How calibration helps with sight problems

This calibration is particularly important for people who are nearsighted, or for those with a variance between the sight in each individual eye – which is probably a lot of us, even if we don’t notice in daily life!

The amount of correction available via the diopter is usually listed in the specifications of the product. The numbers can be helpful, but it’s best to still follow the steps below to set up the lens before first use.

Some glasses wearers find that once the binoculars are properly set up for their eyesight using the diopter, they do not need to wear their glasses to view. This is because the customized binoculars compensate for nearsightedness or farsightedness.

For further information on this, please see our separate guide. All about eye relief: choose and use binoculars for glasses wearers

Is the diopter the same as the focus wheel?

The diopter has a different function to the focus wheel.

By making sure that both the diopter focus and the central focus are exactly as you need them you will be sure to get the best possible image through your binoculars.

On some binoculars, the diopter is part of the right-hand eyepiece. The important role of the diopter is to make sure that any discrepancy between the viewing or focusing capability of the eye is catered for.

If one eye is stronger than the other, then each barrel of the binoculars is individually adjusted to the corresponding eye. By addressing any imbalance, however slight, any chance of eye strain or headaches is reduced.

How to set the diopter on binoculars (diopter on right side)

1. Look at where the diopter is located on your binoculars. It is usually near the eyepiece on the right side barrel, numbered from +2 to -2. Start with it at the center position, often shown by a zero or some kind of marking to differentiate it from the scale on either side.
2. Whichever side the diopter is on, cover that barrel with the lens cap. So with most binoculars that have the diopter on the right-hand side, you will be putting the lens cap on the right-hand side at this stage. It is best to cover the lens rather than closing only one eye. This keeps your viewing eye in its natural position and viewing angle, avoiding any tendency to squint when closing just one eye.
3. Keep both eyes open and look through the binoculars.
4. Find a stationary object in the middle distance to look at. Around 30 feet (8-10 meters) will be fine. Looking at something with high contrast and hard edges will make it easier to get a sharp focus, for example, the edge of a building or a sign with lettering, rather than trees.
5. Use the main focus adjustment (usually on the central hinges) to bring the image into sharp focus. This changes the focal distance for both sides, but of course at this stage you will only be able to view through one eye.
6. Staying in the same place in relation to the object you’re looking at, take off the lens cap and cover the other side of the binoculars instead. Now the side where the diopter is will be uncovered.
7. Keeping both eyes open still, look at the object again. The image may be a little blurry. Don’t touch the central focus wheel. Instead, use the diopter dial to bring that side into sharp focus. It probably won’t need turning much.
8. Remove the lens cap and view the object with both eyes, checking that it is in perfect focus. If not, try the process again.

How setting the diopter helps

The diopter only adjusts the focal distance for the side of the binoculars where it is located. Setting each side separately in this way calibrates the binoculars for any difference between the eyes.

Once you have set the diopter, you won’t need to change it unless your eyesight changes, or you lend the binoculars to someone else with different vision.

Some diopters are lockable, which makes sure that it stays in the position where you have set it. If your diopter is not lockable, it’s worth noting the number setting that suits you in case the adjustment knob gets knocked and moved accidentally.

If the diopter does get moved out of position, it will need resetting to make sure both sides are in focus for you. Otherwise no matter how many times you turn the central focus wheel it will be impossible to achieve a sharp image.

After the diopter is set, just focus with the wheel

From now on, you can just fine tune the focus using the central wheel.

This will focus both sides at once. But now that you have set the diopter, when you change the focus centrally, both sides will remain in the same relation of focus to each other. The result will be a perfectly clear view for you.

If you find that you are having to alter the diopter each time you use the binoculars there may be something out of alignment. Then it’s best to get them checked by a professional.

Different diopters: binoculars with individual focus diopters or a central diopter

If you don’t see a central diopter knob between the two barrels, it means that your binoculars may have separate focusing rings for each side. Each diopter will be able to focus individually.

Other binoculars might have the diopter adjustment on the center column. In this case, it will be likely to be near the main focussing wheel, either in front or behind.

Some high-end models even have the diopter integrated into the focus wheel.

If you have a central diopter, you can still follow essentially the same steps to set the diopter for each eye.

How to set a central diopter on binoculars

1. Start with the diopter at the center position, often shown by a zero or some kind of marking to differentiate it from the scale on either side.
2. Cover the right-hand barrel with the lens cap. It is best to cover the lens rather than closing only one eye. This keeps your viewing eye in its natural position and viewing angle, avoiding any tendency to squint when closing just one eye.
3. Keep both eyes open and look through the binoculars.
4. Find a stationary object in the middle distance to look at. Around 30 feet (8-10 meters) will be fine. Looking at something with high contrast and hard edges will make it easier to get a sharp focus, for example, the edge of a building or a sign with lettering, rather than trees.
5. Use the main focus adjustment (usually on the central hinges) to bring the image into sharp focus. This changes the focal distance for both sides, but of course at this stage you will only be able to view through one eye.
6. Staying in the same place in relation to the object you’re looking at, take off the lens cap and cover the left side of the binoculars instead.
7. Keeping both eyes open still, look at the object again. The image may be a little blurry. Use the diopter dial to bring that side into sharp focus. It probably won’t need turning much.
8. Remove the lens cap and view the object with both eyes, checking that it is in perfect focus. If not, try the process again.

The diopter only adjusts the focal distance for one side of the binoculars at a time. Setting each side separately in this way calibrates the binoculars for any difference between the eyes.

Once you have set the diopter, you won’t need to change it unless your eyesight changes, or you lend the binoculars to someone else with different vision.

Once the diopter is set, it stays

Some diopters are lockable, which makes sure that it stays in the position where you have set it. If your diopter is not lockable, it’s worth noting the number setting that suits you in case the adjustment knob gets knocked and moved accidentally.

If the diopter does get moved out of position, it will need resetting to make sure both sides are in focus for you. Otherwise no matter how many times you turn the central focus wheel it will be impossible to achieve a sharp image.

When the binoculars are properly adjusted and customized to your unique vision, the images that you see will be as sharp and clear as possible.

How to set up the diopters on individual focus binoculars

Individual focus binoculars have a separate focusing mechanism on each side. This diopter on each side adjusts each eyepiece individually.

You can use the diopters to do the left and the right eye separately using the same method already described for regular binoculars with a central focus.

Once the diopter corrections are both set for each of your eyes, they don’t need to be changed unless the binoculars will be used by someone else.

What are fixed focus, focus-free or self-focusing binoculars?

Fixed focus or focus-free binoculars maintain the same focus. Unlike traditional binoculars, they do not have a central focus wheel that adjusts the focus of both sides simultaneously.

They can also be described as self-focusing or auto-focus, though this suggests that the focus can be changed automatically or that the binoculars somehow focus themselves, which is not the case. They are designed to be used for distant objects.

Instead of having their own focus wheel, the idea is that they rely on the ability of the human eye to find its own focus. So it’s more of a ‘natural’ focus, than any ‘auto’ coming from the binoculars.

This type of binocular will still need calibration, using the diopter(s) to suit your eyesight.

Do all binoculars have diopter adjustment?

Some pairs have absolutely no focusing method at all. This does not allow for calibration to suit the potential difference in sight between your left and right side.

Hyperfocal distance: how do fixed focus, focus-free or self-focusing binoculars work?

These binoculars have a longer depth of view, from 40 feet to infinity. That is pretty long!

Everything in the range that they specify should stay in focus. This is described as a large hyperfocal distance.

Advantages of fixed focus or self-focusing binoculars (focus-free)

Speed of use

They are quick and easy to use, making them ideal for watching small, fast-moving birds in the distance. If your bird watching is going to be aimed at distances in excess of 40 feet and don’t want to have to change the focus then these might be a good choice.

Deep field of view

This is large in comparison to regular binoculars.

Easy and simple

Binoculars that you can just pick up and point are simpler than those that need to be focused. Children or elderly people might find these a good solution. If you are using them in a cold environment where you are likely to be wearing gloves then these will be less fiddly.

Simple and robust

They have fewer, less complicated components than traditional binoculars. This has several benefits:

• Their lower production cost means they are cheaper.
• It’s easier to seal them against water and dirt.
• Their robustness means they are well suited to be used intensively in rugged environments.
• With fewer optical elements they tend to be more lightweight.
• Additional visual correction

They are also an option for people who find that regular binoculars do not offer sufficient dioptric correction.

If necessary, people whose eyes need more correction have more flexibility to adjust the focus, with diopters on both barrels.

Disadvantages of fixed focus or self-focusing binoculars (focus-free)

Only for distant objects

Fixed focus binoculars will have a very long close focus distance, usually in excess of 35 to 40 feet. The close focus distance describes how close you can be to an object while still able to focus on it clearly. In other words, this type of binoculars will lack the ability to focus on objects nearby.

Less suited to older eyes

Your eyes have an amazing ability to adapt their focus but this flexibility deteriorates with age. This means eyes over the age of around forty could end up working hard to keep the image clearly in focus.

Less suitable for sharing

Though you have the two diopters, these are only to set up the binoculars to suit your eyes. The diopters are not intended to be adjusted like a normal focus wheel that can be altered according to the distance of the subject you are viewing, or to suit someone else’s eyesight.

Are auto-focus or self-focusing binoculars any good?

The fixed focus or self-focusing binoculars are popular for use in demanding environments, such as on the water or in the cold. They are often chosen for use as marine binoculars.

Their sturdiness and ruggedness might make them worth investigating if your primary interest is bird watching on the water, especially in a cooler climate where thick gloves make it difficult to turn a focus wheel.

Adjusting and setting up new binoculars: next steps

Hopefully this article has launched you on a mission to get the best out of your optics, and to make sure that your binoculars fit your face and are set up exactly for you. Not only will this improve the views that you see, but it will be easier and less tiring for your eyes.

We have further suggestions aimed at helping birders to get the best from their binoculars. Feel free to check out these ideas which are in this article > Binoculars for dummies: the best way to use binoculars properly