Binoculars Fogging Up? Here’s why and what to do about it

If your binoculars fog up inside it can be annoying and it means you won’t have a clear view through them and it’s not that easy to clear them either. It can cause permanent problems too, this is because moist undisturbed places are the ideal conditions for mould to grow. This will inhibit your viewing capabilities and eventually render the binoculars unusable.

Don’t despair though, because it’s reasonably easy to treat internal fogging of binoculars but it can be time consuming.

What Causes Binoculars To Fog Up?

If you think about the windscreen on your car, your glasses (if you wear them) even your windows indoors. They all fog up when subjected to extreme differences in temperature, if say, it’s really cold outside and warm indoors single glazed windows get covered in condensation. That is exactly the same as your binoculars, they fog up due to extreme temperature fluctuations and moisture content in the air.

Going from a warm car to a cold field with your binoculars is more than enough to make them fog up. Condensation forms due to moisture in the air, so if your binoculars are fogging up, then they must have moisture trapped inside them. This reveals a couple of things about your binoculars, firstly they’re probably quite old, and you are storing them incorrectly.

What Types Of Fogging Up Affect Binoculars?

There are two ways binoculars can fog up, internally and externally and one is far easier to cure than the other.

External Fogging Of Binoculars

This is the most common type of fogging up on binoculars and it’s caused by the binoculars being an extremely different temperature to the outside air. Fortunately it’s easy to cure, just wipe the outer lenses with a soft, clean cloth, like the lens cloth usually supplied with binoculars.

Internal Fogging Of Binoculars

This is the worst type of fogging when it comes to binoculars because it’s difficult to use the binoculars if you can’t see through them. It’s caused through the same conditions as external fogging but as it’s on the inside, you can’t wipe the lenses clear. In fact all you can do is wait until the fog clears on its own, and this takes time.

How To Clear Internal Fogging Of Binoculars

To clear the fog from inside the binoculars just follow these simple steps.

1. Place the binoculars in a warm place
   Keep the binoculars in a warm and dry place for a few days. This should allow enough time for the moisture to evaporate into the warm, dry air.
2. Seal the binoculars in an airtight plastic bag
   Once the moisture has dissipated from the inside of the binoculars, seal them in an airtight plastic bag. Add a desiccant bag before sealing, the desiccant should absorb any moisture still contained within the binoculars.
3. Keep the binoculars dry
   When you next take the binoculars outdoors, keep them as dry as possible. If you have to use them when it’s raining, keep them covered as much as possible and as soon as you stop using them, wipe off any moisture and replace the lens caps before putting the binoculars back in their case.
4. Store Them In A Warm, Dry Place
   After each use, return your binoculars to an airtight plastic bag in a warm, dry place. This should prevent them from internally fogging up.

Alternative Ways To Remove Internal Fogging Of Binoculars

There are other methods for removing or preventing internal fog forming in your binoculars. Before trying any of these consult your users manual first as some of these methods might not be applicable. Only use a lens cloth specifically designed for cleaning lenses. Using any other cloth will run the risk of scratching and/or permanently damaging the lenses.

Remove The Lenses

On some binoculars it is possible to remove the lenses by unscrewing them. They can then be gently wiped using a lens cloth to remove any foggy moisture residue. Consult your users manual before attempting to remove the lenses as not all binoculars have this function. Before removing the lenses, clean the exterior of the binoculars with a clean soft cloth and use an airbrush to remove any dust or minute particles that could cause problems later on.

Anti-Fog Products

There are a plethora of anti-fog products available to prevent fog forming on the lenses of your binoculars including;

• Sprays
• Drops
• Creams
• Wipes
• Cloths

These can be carefully applied to the external lenses of binoculars to cut down on fog build up. Check with your binocular manufacturer before purchasing any anti-fog product as they may not be compatible. And could possibly void any warranty you might have on your binoculars.

Wipe With A Lens Cloth

To remove external moisture (fogging) from the lenses of binoculars just clean gently with a lens cloth. Lens cloths are specifically designed to be gentle enough on lenses so they won’t damage them. Under no circumstances use any other type of cloth on the lenses of binoculars, to prevent damage.

The Spit And Polish Treatment

Using human spit works well to remove external fogging and prevent it from reforming. So it makes a natural anti-fog treatment. Just spit on to the lens and wipe with a lens cloth, ensure there’s no grit on the lens before spitting as grit could damage the lens permanently if you rub it into the lens.

The Slow Temperature Acclimation

If you allow the binoculars to slowly acclimatise to current weather conditions they’re less likely to fog up. This does mean keeping them outside in the cold conditions for up to an hour before using them. Unless you can keep them under constant surveillance this method does involve some risk of theft. 

One solution is to keep them in a locked car with the windows slightly open. If you decide to try this be sure to keep the binoculars out of sight as this could also lead to theft.

Consider Purchasing A New Pair Of Fog Proof Binoculars

Many modern binoculars have been gas purged to remove moisture rich oxygen and replace it with an inert gas. Gasses like nitrogen and argon contain no moisture and therefore cannot react to sudden extreme temperature changes. The gasses are sealed inside the lens tubes which prevents any mould spores etc from entering, which will ensure no mould growth.

The thing to remember if you are purchasing a new pair of binoculars is that not all waterproof binoculars are fog proof. Be sure to check specifically that the pair you’re considering to buy actually state in the specifications that they are fog proof. This will not prevent the external lenses from fogging up, but that is easily remedied using a lens cloth.

Frequently Asked Questions