condensation on lens at night

-Josh-

-Josh-

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Josh
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I was doing some large format, long exposure shots at night, and after the first hour or so my lens fogs up with condensation. Is there anyway to stop this? I dont want to have to cover the lens at any point as I'm trying to catch star trails.
Thanks.
 
Yep, keep it warm. Easiest way is to wrap 2 disposable hand warmers round it. Keep them away from the body though since you don't want to heat up the sensor(assuming you're shooting digital)
 
I'm shooting large format. What do you mean by hand warmers? those things that heat up when you crack the thing inside?
 
As you will no doubt know; condensation appears on items where there is a difference in its temperature to that of the moist atmosphere you introduce it to (e.g. warm & dry to cold and moist, or colder but dry to hot & humid, etc, etc).
Therefore when you get your camera gear out to take pictures in this sort of weather the outer glass of the lens (or filter, if fitted) will fog up.

I did a quick search on here using 'condensation' as the key word and found a ton of threads, many covering this sort of topic. The following post of a thread provides a good idea that should go a good way to overcoming this:

http://www.talkphotography.co.uk/forums/showpost.php?p=2047062&postcount=9
 
All the other threads are more for introducing the camera from one extreme to another. My problem is I'm getting condensation on the lens from it being left in the cold for so long. I suppose it isnt really condensation, dew maybe? It covers the whole camera but its just the lens I'm worried about as I dont want it obscuring the image.
 
There's a couple of options, I face this issue a lot with my Astronomy gear. As a simple dew shield, that will help somewhat, cut a piece from a foam camping mat, you want it about 1.5x as long as the diameter of the barrel of the lens, although you may have to reduce that depending on the focal length (it works for my nifty... and my Skymax 102). Wrap it, I've taped mine with duck tape and slip it over the front of the lens barrel. A lens hood may help somewhat instead. During the capture process, if the lens starts to fog, a gentle application of a hair dryer (low heat) from a distance will clear the fogging nicely. The other option would be to invest in some dew tapes. These are heating coils that wrap around the lens, can be powered from batteries, and keep the dew at bay. (I really need to get me a pair).
 
Steve Smith said:
You want to keep it at the same temperature as the air around it. Condensation will occur on a surface which is warmer than ambient.


Steve.
Click to expand...

No, condensation will occur when air is cooled to below it's dew point/saturation temperature. Cold air contcting a warm lens will be heated and you won't get any condensation, hence the advice above about heating coils or hair dryers. The resaon you are getting condensation on the lens at night is that the lens glass is solid, and can loose heat by radiation, which the air can't. Thus the lens surface is actually colder than the ambient temperture - the same way the ground is. The water droplets that form on the lens are formed the same way dew forms on the ground at night.

All you need to do is keep the lens glass a few degrees above ambient temperature. There are custom made heating devices available, and if you have mains power the hair dryer method works very well.

What I do is get some chemical hand warmers from an outdoor shop - the one use disposable kind, like a bag of powerded in a plastic wrapper. When you take the wrapper off and expose the power to air they get hot. Wrap two around the lens, secured with a rubber band and that's it. Be careful since some of them get VERY hot and may need insulating from the plastic on the lens.
 
One of thos little fans for keeping your face cool on the beach can be directed across the front element of the lens. As long as it's not too dewy a night, the air movement the fan causes should keep the front element clear. Use a seperate tripod (it's a good use for thay carppy one you got for a fiver at a car boot...) so that the vibrations don't upset the exposure!
 
The best and most reliable way to prevent your lenses from fogging is to use a heated band that wraps around the lens body. They are usually 12vdc powered and gently keeps the lens above the dew point.
Search for " telescope dew heater " on google. There are many makes and options !!
I use the Kendrick system on my telescope and it works wonders on my dlsr lenses too !
 
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