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How to Dew-Proof Your Camera Lens

Windmill Milky Way ruined by dew

Don’t let condensation ruin your astrophotography!

I was recently reminded of the common problem of dew on your lens ruining an astrophotography shoot. Usually, where I shoot, the conditions don’t cause an issue with condensation on my lenses, but sometimes, just often enough to catch me off guard, it does, and my night of AP is wrecked by blurry and faded-out images — especially when I’m shooting time lapse and star trails.

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Tanja, our friend Brendon Wainwright, and I were shooting star trails sequences right next to each other. Brendon was using a Nikon 20mm f/1.8 lens, Tanja used a Canon 24-70mm f/2.8, and I was shooting with the Canon nifty fifty 50mm f/1.8. None of us felt the humidity in the air, and we left our cameras out shooting and took a nap.

A few hours later we woke to check our cameras, and much to his dismay Brendon had gotten only about 5 exposures out of the hundreds that were shot before the lens fogged over with dew. Both Tanja’s and my lenses were perfectly dew-free. We made a few jokes about it maybe being a “Nikon problem” because Tanja and I shoot with Canon, and that’s when Brendon admitted he had forgotten his lens hood. Protecting your shoots from fogged-over ruin is sometimes as simple as that.

Lens dew splitscreen
Lens dew causes the image to wash out and look out of focus.

Why does lens condensation happen?

Condensation, dewing or fogging up of camera or telescope lenses, happens because the glass of the lens is colder than the air around the lens. That’s not enough, though. There also has to be some humidity in the air.

In physics terms, it is the change in the gaseous form of water in the air, as water vapor, to liquid water. Gases are warmer than liquids, so if the water vapor in the air hangs around the glass of the camera lens, which is a better thermal conductor than air, it will cause the heat to be removed from air making contact with the lens, and turn the gaseous-state water vapor into tiny droplets of liquid water, which cling to the lens and wreck everything for us!

How do we keep the dew away?

Lens hoods

Lens hoods (like these) are the most practical and quick way to keep dew at bay. Most people already have them, so if you do just make sure you use them in all cases.

Having the lens objective glass recessed helps to protect it from the outside colder air just a little longer. For obvious reasons lens hoods aren’t viable on ultra-wide lenses, so you’re somewhat limited.

Pros:
Cheap (sometimes)
No power required
They make you look like a pro

Cons:
They only work in low-humidity
They don’t work as long as other methods
They work best on longer-focal length lenses

Hand warmers

hand warmers
Hand warmers create heat without power

One step better than a lens hood that also takes no power (a big plus), is wrapping a couple of hand warmers (like this) around the lens hood or directly around the lens objective. Use a rubber/elastic band to hold the hand warmers around the lens or lens hood, and a layer or two of cloth to insulate everything.

Hand warmers work pretty well because they help to create a slightly warmer air pocket near the objective of the lens so it helps to keep that nasty water in its gaseous state.

Pros:
Cheap
Lightweight and easy to carry
Lasts an entire night
Easy to use
No power required

Cons:
Only lasts 1 night
Can be difficult to focus with them on
Somewhat unreliable
Causes waste
Not always effective in very cold conditions

Heating strips

Dew heater strips (like this) are very effective at keeping the condensation at bay. They wrap around the lens hood or objective glass area of the lens and apply electrically-induced heat directly to it. The idea of them is very similar to using hand warmers, but it is much more effective because you control the heat.

One major downside is they can be expensive, as they require a power source and a controller module (like this) that regulates the heating elements inside. If you don’t have to go far on foot and/or have access to power, they are a great option.

Pros:
Very reliable
Very effective
Lasts as long as you have power

Cons:
Requires power to work
Can be heavy (power source)
Can be expensive
Electronics can be bulky and untidy
Temperature must be regulated

Moving air (a fan)

dew fanThis one is my favorite. If you’ve been shooting at night for long, you may have noticed that the worst nights for dew are the ones where the air is perfectly still. Just a slight breeze can make conditions perfect. Even a very small bit of moving air keeps the condensation away!

While it takes a little bit of DIY to get it done, it is very cheap and works wonders. A small, smooth-running, 12-volt computer fan can be mounted near the camera lens to create a small amount of moving air. You can even use a 9V battery to power them for a while at a lower speed. I mount mine on a magic arm, connected to the tripod with a clamp or directly to the camera body with the hot shoe adapter.

The first question I get from anyone always is “What about vibration?” I can speak from experience that it isn’t an issue, assuming you have a nice and smooth running (quiet) fan. Obviously it’s best not to attach the fan to the lens itself, but the hot shoe is fine.

Pros:
Extremely effective in most conditions
Very reliable
Lasts as long as you have power
Doesn’t require temperature regulation

Cons:
Requires power to work
Power source can be heavy
Electronics can be untidy and difficult to position

What works for you?

Depending on your shoot location you may or may not need extreme dew protection, but chances are you’ll run into the problem someday. Which methods do you use to keep your astrophotography shoots successful and condensation-free?

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About the author

Cory Schmitz

Co-founder of PhotographingSpace.com, co-owner of several telescopes and mounts, too many cameras, and not enough hard drives, Cory is an American expat living in South Africa with his wife, Tanja Schmitz.

An avid astrophotographer for timelapse, deep-space imaging, lunar, planetary, and star trail imagery, he is an all-around jack-of-most-trades for night-sky photography.

He is also an internationally published and commissioned astrophotographer, where his photos have been used in multiple online and print publications.

15 Comments

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  • Love the fan idea. I bought a few last year for a telescope project and have some left. I’m off to bodge up a camera fan as my dark sky site is very near a river and dewing is a major problem. Cheers Cory!

    • Hi Soupy,

      Rivers are the worst. With rivers it’s sometimes not always just water vapor, but sometimes even droplets in the air! I was near a waterfall last weekend and the humidity was terrible.

      Best of luck, and I hope it works for you!

      Cheers,
      Cory

  • Kendrick dew heaters are the best. I use an 120A/hr battery to power the scope, cameras, and dew heaters. There is no excuse for not being bold.

  • I have dew-not strips for my OTA and guide cam OTA. Like you say, they’re the best and easiest if you have power. But I’m heading out on a trip soon and that hand warmer idea is fantastic! Definitely looking into that, thanks!

  • Thanks for the range of ideas – the fan looks great.

    A physics correction: the lens is not colder than the surrounding air, but is a better conductor. This allows the heat to be removed from the surrounding moist air, changing the water vapour into liquid.

  • The fan idea is great! I also have another one, works great for me: There are USB-powered gloves with heaters on Amazon for only a few bucks. I bought a pair, got the heating pads out, taped them to my lens hood and wrapped them in aluminum foil. Now I only need a USB power station / batterie to heat them for days. Normally, I only activate them for a few minutes to heat the gear up, because when they constantly run, I get problems with blurry stars (something like bad tube seeing in large telescopes).
    Cheers
    Björn

  • La verdad es que la condensación me ha arruinado muchas sesiones de fotos después de pasar noches en vela para nada. Es un serio problema. Intentaré la solución del ventilador, parece sencilla.

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