Everything You Must Know About Fog Proof Binoculars

Everything You Must Know About Fog Proof Binoculars

We get asked questions about fog proof binoculars almost daily here at Binocular Base, so we’ve put together this article in answer to all of those questions. There are so many claims about waterproof or fog proof binoculars, it can be confusing, but don’t worry, we’ll clear it all up in this post. The first place to start is to explain why binoculars fog up.

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Why Do Binoculars Fog Up?

The short answer is extremely rapid changes in temperature cause binoculars to fog up. This is because the lens tubes have oxygen trapped inside. As oxygen contains a certain amount of moisture, it reacts to those sudden temperature changes and fogs up the inside of the lenses as the moisture condenses. 

How Do Manufacturers Make Binoculars Fog Proof?

It’s simply a case of removing the oxygen and replacing it with an inert gas like argon or nitrogen that contains no moisture. As they contain no moisture, they cannot react under temperature fluctuations and so the binoculars can’t fog up. You’ll often see on the binocular specs “nitrogen purged”, this means all of the oxygen has been purged from the lens tubes and replaced with nitrogen.

The lenses have to then be sealed to contain the gas within, this makes the binoculars waterproof and dust proof too. Of course the outside lens can still become fogged up, but that can be cleared using a soft lens cloth. The internal lens surface will remain fog free.

What’s Better Nitrogen Or Argon?

If you do a quick search for this exact term, you’ll find lots of online forums where experts argue these points quite succinctly. All offering good reasons why one’s better than the other, here’s a quick summary of all we’ve found.

Argon Gas (Ar)

Some argue that as argon molecules are larger than nitrogen molecules, it will work better over a wider range of temperatures. They also say that argon has more resistance to diffusion, so in plain English it won’t leak out of the lens tubes easily. Which means the fog free environment will last longer.

Nitrogen Gas (N)

Others say that nitrogen, argon or any other gas that’s non-reactive will work just as well. They say any dry gas will work, as it’s the moisture content in oxygen that causes the problem.

Alternatives To Nitrogen Or Argon

There are a few binocular manufacturers who fill their binoculars with a mixture of argon and krypton gas. They claim that this improves on the fog proofing even more by pretty much eradicating the effects of thermal shock. They also claim that this blend has far larger molecules and so will last longer.

Added Benefits Of Oxygen Purging

Back in the dark old days, before fog proofing binoculars was possible, many binoculars suffered from mould growth. Spores used to enter the lens tubes and grow up against the inside of the lenses. This being the perfect conditions for mould growth, light, undisturbed with added moisture.

Since the introduction of oxygen purging and replacing it with an inert gas, even if the mould could enter, it wouldn’t survive. But as an added bonus, the tubes are sealed and so no mould spores can enter.

Waterproof Binoculars

To make the binoculars fog proof, they have to be sealed so the gasses cannot escape. By sealing the gas in, nothing else can enter, like water. So all fog proof binoculars should be waterproof too. Unfortunately that doesn’t work the other way, waterproof binoculars can be completely sealed but they can have oxygen sealed inside the tubes.

This means they won’t allow water to enter, but as they contain oxygen, they can still react to sudden changes in temperature. So be sure they are purged by either nitrogen or argon or any other combination of gasses.


How Do They Create Waterproof Binoculars?

Just because a pair of binoculars has a rubber casing does not make them waterproof. True waterproof binoculars have rubber O rings that seal the joints, and the interior of the lenses are nitrogen purged and then sealed to prevent any gas escaping or water entering.

What’s In A Name?

When it comes to binoculars being waterproof there’s much confusion, and it’s easy to see why. We often see terms like “weather-proof”, “weather-protected”, or “water-resistant” which although implies some level of protection, doesn’t really specify anything. If you actually see the word waterproof on the binocular specs it should be backed up with more information.

This is where the industry code for waterproofing comes in. This code applies to anything and everything really from electrical sockets to bathroom fixtures, mobile phones to binoculars. To be honest the code can be slightly confusing so just to summarise, IPX6 will withstand rain from any angle and IPX7 will withstand up to 30 minutes submerged in one metre of water without any ingress.

So any binoculars with an IPX6 will be perfectly capable of withstanding anything the Great British weather can throw at them. Whereas IPX7 is only about total immersion in one metre of water for a maximum of 30 minutes.

Hermetically Sealed

If you see this term applied to a pair of binoculars it simply means that the seal is completely airtight.

Is Waterproofing And Fog Proofing Necessary?

As we live on a planet made up of more than 70% water, and in a country where the seasons are differentiated by the temperature of the rain, we believe it is absolutely necessary to have both waterproof and fog proof binoculars. As this process is fairly common practise now amongst the top quality binocular manufacturers, waterproofing and fog proofing come at no extra cost.

I’m Not Going To Take My Binoculars Out In The Rain Why Do They Need To Be Waterproof?

On the face of it, it would seem that you don’t need waterproof binoculars. But there is always some degree of moisture in the air which can enter the lens tubes of binoculars and cause you problems. 

Plus even if you don’t go out in the rain, that doesn’t mean it won’t rain before you return home.

Are All Binoculars Waterproof?

No, not all binoculars are waterproof, terms like  “weather-proof”, “weather-protected”, or “water-resistant” actually mean very little. You need to check the IPX code for the true level of waterproofing on any pair of binoculars. Not all waterproof binoculars are fog proof, but all truly fog proof binoculars are waterproof.

What Are The Advantages Of Waterproof & Fog Proof Binoculars?

Having a pair of waterproof and fog proof binoculars has a far greater advantage over non waterproof and non fog proof binoculars the advantages include;

  • Longer Lasting
    Having binoculars that are filled with an inert gas protects them against water damage, prevents mould growth and stops any dust from entering the lens tubes. This means they will give you many years of perfect service.
  • Far Better Construction
    Waterproof and fog proof binoculars undergo rigorous tests to ensure they are of a top quality construction. This applies to every aspect of the design.
  • Saves Money (In The Long Run)
    As these waterproof and fog proof binoculars will last for many years and never alter their condition, they will prevent you from needing to buy any replacement binoculars for many years.

Where Can Waterproof & Fog Proof Binoculars Be Used?

The short answer is everywhere. They are suitable for ;

  • General Use
  • Marine Use
  • During Rainstorms
  • In Areas Of High Humidity
  • Deserts
  • Beaches
  • Dusty Environments

Frequently Asked Questions

What are fog proof binoculars?

Fog proof binoculars are binoculars that have been purged of oxygen which has then been replaced with an inert gas . This gas is sealed inside the lens tubes and as it contains no moisture, it cannot react to sudden temperature fluctuations.

Are waterproof binoculars worth it?

Waterproof binoculars are definitely worth it. Because even if you never go out in the rain, there is always moisture in the air which can enter the lens tubes and damage the binoculars.

What does nitrogen purged mean in binoculars?

If you see nitrogen purged in the specs, it means the manufacturers have purged or removed all of the oxygen from the lens tubes and replaced it with nitrogen gas. Because nitrogen contains no moisture, it cannot react with extreme temperature changes and won’t fog up.