Camera Lens fogging up outside
August 12, 2013 8:55 PM   Subscribe

I'm tent camping and trying to get pics of the night sky. My lens just started fogging up. What do I do? My plan was to set my wireless interval timer up and go to sleep but now it looks like I'll have 400 blurry pics. It's a canon f/1.8 50 mm with a uv filter. It's 65 degrees here with 81% humidity.
posted by desjardins to Sports, Hobbies, & Recreation (9 answers total) 1 user marked this as a favorite
81% humidity with falling temperature is your problem. You got any kind of heat source, at all? That's really your only option... the only way to stop fog forming on the lense is to raise its temperature above the dew point.
posted by Jimbob at 9:00 PM on August 12, 2013

Warm the camera. Or, dry the air about the camera. A friend of mine who does night sky photos puts the camera on a small tripod, in a cut down 5 gallon plastic bucket, and puts several desiccant packs around and under the camera tripod. In all but windy conditions, the bucket seems to keep local air around the camera still enough for the desiccant packs to cut down the humidity enough to prevent fogging for several hours, even down here in Florida.
posted by paulsc at 9:12 PM on August 12, 2013 [1 favorite]

In addition to warming the camera, take the UV filter off, as you won't need it for photographing the night sky. This will at least minimize the number of surfaces that could fog up.
posted by theory at 9:22 PM on August 12, 2013

My only heat source is a propane lantern.
posted by desjardins at 9:25 PM on August 12, 2013

Can you use the lantern to warm up, say, a blanket or jacket, then drape that over the camera body? I guess you still won't get much sleep, doing that...
posted by Jimbob at 9:40 PM on August 12, 2013

Another strategy that might help in a camping situation, is to recognize that air near the ground may be moving least, and carrying greater humidity than air at higher elevations. If your camera is near the ground, is there some way you can get it up higher, by at least several feet? Suspend or mount it on a tree limb, perhaps, if that doesn't wreck your field of view? (I presume you're trying to photograph the meteor showers...)
posted by paulsc at 9:42 PM on August 12, 2013 [1 favorite]

Heat radiates from any object (such as your camera lens) to the sky. Then, in the conditions you are in, if due to this radiative cooling the lens becomes even 0.25 degrees cooler than the ambient air, it becomes a dew collector.

Astronomers taking night-time photos, either with cameras or various telescopes and astronomical gear, tackle this two ways:

1. Heat applied to the optics (or preferably, to the tube just below them) to keep them warmed above the temp of ambient air. Commercial units with battery, controller, flexible heating wire are widely available.

2. A dew shield that partially or completely shields the lens from the open sky, stopping the radiative cooling.

You could make a dew shield out of just about anything, like maybe a sheet of black construction paper or cardboard that would roll into a tube and fit over your camera objective.

Examples 1, 2, 3. Those are all commercial products but you can rather easily cobble together something that does the same thing from available materials--cardboard, maybe a piece of insulating material from a water heater blanket or automobile window shade, some duct tape. You're shooting for something maybe 2X as long as the diameter of your camera objective lens. (Like if your camera lens is 2.5 inches across you want a tube 2.5 inches in diameter and 5 inches long, approximately.)

An article on dealing with dew for nighttime camera shots.
posted by flug at 1:20 AM on August 13, 2013 [1 favorite]

Dew removal is a major thing for astronomers and astrophotographers. There are all kinds of heaters designed for telescope lenses and even finders and eyepieces. This one is made for digital SLRs, to deal with your exact circumstances.
posted by mcwetboy at 4:32 AM on August 13, 2013

A dew shield is really simple and makes much more difference than you would think. That said, it's a bit easier on a telescope since you have a narrower field of view than a camera lens so you can make it nice and long. With a 50mm lens you may struggle to make something that both shields and doesn't obstruct the field of view.

One other possible tip is using a small 12V travel hair dryer in a cigarette lighter socket, if you have one to hand. They're probably rubbish for drying hair, but you don't need a lot to warm a lens above the dew point. Use it sparingly though.
posted by edd at 6:08 AM on August 13, 2013

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