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Old September 14th, 2018, 01:14 PM   #1
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How to prevent lens fogging?

I've been shooting a lot of time-lapse stuff at night lately, and have had some trouble with condensation forming on the lens. Is there any way to prevent this?
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Old September 14th, 2018, 02:09 PM   #2
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Re: How to prevent lens fogging?

I've seen those tiny fans that are USB-powered, wonder how long that would run if connected to one of those USB cell phone power bank battery things? And blow across lens?
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Old September 14th, 2018, 02:38 PM   #3
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Re: How to prevent lens fogging?

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Originally Posted by Ray Dunakin View Post
I've been shooting a lot of time-lapse stuff at night lately, and have had some trouble with condensation forming on the lens. Is there any way to prevent this?
Beating the laws of physics is tough. You get condensation in general where you have a surface that's colder than the ambient dew point. For example, a cold camera lens that's carried into a warm house will often end up condensing some moisture onto its surface.

To avoid this, either raise the surface temperature of the lens above the ambient dew point, warm up the air so that the dew point actually decreases to a point below the surface temperature of the lens, or dry out the ambient air so that the dew point decreases. Of these, I'm thinking the first is the only field-worthy solution.

EDIT: Of course the obvious thing is to arrive hours early, set up your camera, and let it acclimate to the ambient temperature. If the surface of the lens is the same as the ambient temperature you'll be as safe as you can be. Typically in your location, it's rare for the air temperature to fall below the dew point. But when it does, you get dew plating out on everything, from leaves on the trees to the rocks on the ground to, yes, your camera lens. Under those conditions, you just have to live with it. Happens on my side of the country all the time.

Just for fun -- what we're talking about here is why water beads up on a cold drink in the summer time. Because the surface of the drink is, say at 0C (freezing point of water, so ice), while the dew point on a fine summer's day might be in 10-20C. So any air near the surface of your drink drops in temperature toward the surface temperature of your drink. As it decreases in temperature past the dew point, it has to drop some of that moisture (you can't have more than 100% relative humidity), so dew plates out on the surface of your drink.

Then it gets interesting. The formation of dew is accompanied by the release of the latent heat of vaporization (yes, that's a real thing). That is, it takes less energy for water to be a liquid than it does for it to be a vapor. So when you condense the vapor out of the air and plate it onto the surface of your drink, it also releases the energy used to vaporize it in the first place. But where to? Why, into the surface of your drink. Which warms up your drink. Which is why your ice melts.

Ain't physics fun?

Last edited by Bruce Watson; September 14th, 2018 at 03:04 PM. Reason: To add way more information than anyone really wants. ;-)
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Old September 14th, 2018, 05:29 PM   #4
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Re: How to prevent lens fogging?

Lens temperature is about the only condensation variable that you can somewhat control in the field. I use this powered off the same external battery that is powering my camera:

https://www.amazon.com/PROTAGE-Conde...dp/B073X18JND/
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Old September 14th, 2018, 07:37 PM   #5
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Re: How to prevent lens fogging?

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Originally Posted by Bill Ackerman View Post
Lens temperature is about the only condensation variable that you can somewhat control in the field. I use this powered off the same external battery that is powering my camera:

https://www.amazon.com/PROTAGE-Conde...JND//din02c-20
Thanks, I'll give that a try!
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Old September 14th, 2018, 10:24 PM   #6
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Re: How to prevent lens fogging?

Use a filter. Go to your local motorcycle shop and get a small bottle of helmet visor anti-fog. Usually comes in a little thumb squirt spray bottle. Spray on and and wipe of excess with a soft cloth/lens cleaner. Usually works for hours.

If you are really stuck do what we used to do years back. Chop up a potato into smallish cubes and drop them into a Zip Lok bag. Grab a cube and glide it around the lens filter. This deposits a micro layer of starch on the filter. The starch tends to inhibit the formation of condensation. Motorcyclists used to use this trick also.

Another trick I used to use in the UK winters was to have the camera on the passenger side floor in the car with the foot well heating on. Get the camera quite warm and it will be a while before the condensation forms when you get out. This also helps to stave off lens internal condensation issues.

Of course some of this may help or it may not as there are so many variables to effect condensation.

Just some previous experiences. In Asia on jobs we used to leave the cameras outside until they had acclimatized. If you took them straight out of the hotel room air con they would condense up straight away and would take ages to acclimatize. We used to have to ask taxi drivers to turn of their AC and open the car windows. Otherwise a ten minute trip in an air con taxi would cause the lenses to condense when we stepped out of the cab. The cabbies used to think we were mad. A 12v portable hair dryer also cures the problem fairly quickly.

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Old September 15th, 2018, 08:55 AM   #7
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Re: How to prevent lens fogging?

I've had this problem in the past mostly with DSLRs but with one of my lenses the condensation occurred on the inside of the front of the lens so there was no way to actually get at it, a few times i've experienced it on the mirror of a DSLR too.

I've heard of advice of putting the cam in a sealed plastic bag and slowly allowing it to get to the ambient temperature, but this can take up to an hour. Not great at a live event.

Last time I was confronted with this, i had two cams, one left in the cold for outdoor stuff and another one kept warm for indoor shots.
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Old September 15th, 2018, 07:38 PM   #8
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Re: How to prevent lens fogging?

The heater Bill suggested is similar to what has been common on telescopes for years. They need to keep the temperature above the dewpoint. Plastic lenses might be a challenge.
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Old September 18th, 2018, 08:01 PM   #9
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Re: How to prevent lens fogging?

Try smearing shaving cream on your lens and wiping it dry with a cleaning cloth. I've used this method when I was doing underwater filming on spawning salmon. Going suddenly from the warm air temperature to the cold water would always fog up the glass in the underwater camera jacket so this little trick would work very well for an hour or so. Simply reapply the shaving cream from time to time as needed.

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Old September 19th, 2018, 12:05 AM   #10
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Re: How to prevent lens fogging?

Now I like the sound of that. Must try it out. When you say shaving cream do you mean the foam type or the gel type? Either way I'm going to test it out some time.

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Old September 19th, 2018, 10:40 AM   #11
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Re: How to prevent lens fogging?

I can't remember which one I used. Try them both out and see which one is more effective. I just tried gel on the bathroom mirror and blew my hot breath on it and it didn't fog up.
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Old September 19th, 2018, 12:10 PM   #12
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Re: How to prevent lens fogging?

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Originally Posted by Leon Lorenz View Post
Try smearing shaving cream on your lens and wiping it dry with a cleaning cloth.
Any idea what that might do to your lens' coating? I'm thinking it's probably not good for it. How about doing that to a UV haze filter instead?

Better yet, how about using a product like Rain-X anti-fog? Again, on a UV haze filter on the lens. They even sell them as wipes in individually sealed packets which would be nice for field use.
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Old September 19th, 2018, 08:16 PM   #13
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Re: How to prevent lens fogging?

Will try all suggestions. Good ideas folks!

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