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Why Do Binoculars Fog Up? | Optics and Lab Equipment

Why Do Binoculars Fog Up?

Last Updated: 21.10.19


The image quality ensured by binoculars depends on a variety of factors ranging from the magnifying power delivered to the lens and prism coatings used and whether they’re fog proof or not. Reading adults’ and kids’ binoculars reviews before buying binos is thus mandatory yet there are some things you can do if you end up with your optical instrument fogging up. 

Many outdoor activities are enhanced thanks to all sorts of tools and instruments such as spotting scopes and binoculars. Whether you’re interested in birdwatching, hunting, or admiring nature’s beauty in great details, binoculars are a must. 

The efforts of many inventors and scholars have made it possible for us to now use advanced binoculars that render the whole outdoor experience remarkable. Thanks to the latest achievements in this field, it is now relatively easy to find good binoculars at a decent price. 

However, despite the great specs binoculars may come with, there are some weather conditions that might affect your visual experience when using them to view the objects of interest. If the model you’ve chosen is not fog proof, it is more likely for you to end up with internal fogging of the lens and thus with an unclear image. 



How fog forms 

Many binoculars available for sale these days claim to be fog proof and waterproof. Even some cheaper models feature such specs. It is not uncommon to get binoculars that promise to prevent fog from forming and still end up with such unpleasant events and thus with reduced image clarity. 

Fog forms in certain conditions and it occurs when a cool mass such as a cold surface area and high humidity meet. It can easily form near lakes, coastlines, and tropical locations. Such areas are often preferred for birdwatching and, since binoculars are involved in this activity, you might end up with a foggy view. 

Small water droplets collect on the lenses and body of the binoculars you use. When that happens, it takes 15-20 minutes or even longer for the fog to naturally dissipate, which means that the instrument cannot render clear images until the fog has completely disappeared. 


Internal and external fogging

When you expose your binoculars to temperature/humidity changes, fog can form on the outer and inner parts of your device. While external fogging is easier to deal with since you can easily wipe away minute water droplets by using a soft cloth, it is a bit more difficult to deal with internal fogging. 

Some models make it quite difficult to reach the inside of the binoculars if you need to clean the inner part of the lens. However, if you use binos that allow you to do that, you have to make sure you clean the parts properly in order to avoid any damage. Fine dust particles may scratch the lens if not removed carefully. 

Not to mention that internal fogging might also lead to fungus growth, which can further damage the binoculars. If, however, your binos have fogged up inside, there are a few simple things you can do to solve this problem. 

If the fog doesn’t dissipate rapidly and thus you are no longer able to use the device, make sure you leave it in a warm place for a few days. Since many models are not airtight, the moisture formed inside should evaporate. Make use of commercial desiccants to absorb the moisture. Seal your instrument inside an airtight plastic bag, add the desiccant, and let the product do its job. 



Anti-fog binoculars 

To avoid interrupting your birdwatching or outdoor activities because of a foggy view, it is best to get fog-proof binoculars if your budget allows you to do so. Today’s market offers binoculars that were specifically designed to overcome such issues. 

Argon and nitrogen are usually used for such optical devices. Models that were built with these gasses will prevent internal fogging from occurring and are usually described as being nitrogen-purged or nitrogen-filled units. Still, this will help you keep your binos fog-free inside and does not mean that fog won’t form on the outer parts of the device. 

That’s why some manufacturers make use of anti-fog finishings to prevent small water droplets from sticking to the outside surface of the lens and thus from fogging. These water-repellent substances applied might help you enjoy a fog-free view for a long time as long as you clean the binoculars properly and regularly. 


How to prevent binoculars from fogging up 

If you cannot afford to buy fog-proof binoculars or you have an older model that you’re satisfied with, there are some simple things you can do to prevent your instrument from fogging up and thus your activity from being interrupted. 

A simple and quick way to make your binoculars fog proof is to use anti-fog products. The market now offers a variety of such items ranging from anti-fog wipes to sprays, creams, and drops. These products are usually applied to the lens surface to reduce fog condensation. 

The efficiency of these treatments varies from one product to another. Some of them offer fog protection for a few hours while others may help you keep your binoculars fog-free for a week or so after it has been properly applied. Just make sure that you use a product that suits your binoculars and that the manufacturer recommends. 

Desiccants are also appreciated for helping binoculars stay dry and absorbing moisture whenever it builds up. There are various such products available these days and they are easy to use and quite effective. You can even use rice or silica gel as a desiccant. 

Just put your binoculars in an airtight bag such as a ziplock bag along with the desiccant and leave it so for 24 hours or more. You can employ this method for spotting scopes, monoculars, and various electrical items. 

Another simple way to prevent fog from building up is to let the binoculars naturally adapt to the local humidity and temperature. It’s true that this might not be always possible but it is worth trying whenever you can. 

Keep the binoculars in a dry place whenever you don’t use them and thus minimize fog exposure. Use an airtight bag and add a desiccant to it. If left uncontrolled, fog exposure can promote the growth of fungus that may damage your device. Even if the moisture inside the binoculars has been removed, make sure that you keep the instrument as dry as possible when going out. 

Whenever fog builds up and you want to remove the moisture to enjoy a clear view again, it is highly important to make sure you don’t wipe it roughly. Doing so may damage the lens coatings applied, especially if there are dirt or dust particles that got stuck to the lens. 

Since fog may reform if you don’t use anti-fog products to provide you with fog protection for longer, repeated cleaning is required in order to use the binoculars and see things clearly. Removing dust and moisture must be done carefully in order not to harm the fragile finishings applied to the lenses, though. 

Overcleaning may thus cause more harm; therefore, clean the instrument when it is absolutely necessary. If it is clean yet moisture has formed, make use of a soft cloth and gently wipe away the extra moisture that has built up. 



Factors to consider before choosing fog-proof binoculars 

There are many things to take into account when buying binoculars. From the magnifying power they provide you with to the field of view ensured, everything counts. The fog and weather resistance ensured by the binoculars you use is of great importance, too. 

Therefore, consider the outdoor activities you engage in and that require the use of binoculars as well as the weather conditions of the locations you frequently go for. It is best to buy binoculars that not only offer protection against fog but that are also waterproof and weatherproof. 

Thankfully, most binoculars that are fog-proof are also waterproof, so you will get to address two main issues at the same time. A waterproof body means that water cannot enter the unit. Such items can even stay underwater for a brief time before they can be damaged. 

Not allowing water inside the binoculars is mandatory in order to keep the binoculars functional and allow them to ensure high-quality images. By not allowing any water in, you can also prevent moisture and fungus from building up. 



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