Gear Talk > EOS Bodies - For Stills

anyone have any cures for lenses fogging/dew during astrophotography?

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risc32:
I've only recently had this happen but now that i'm doing more of this thing it's bound to happen all the time. I was really surprised to see it on my images. I didn't see a thing on the LCD out in the field, but i'll be looking closely in the future. I've added an image that most clearly shows the problem. thanks

Mt Spokane Photography:
Presumably you let the camera and lens cool down for a few hours first?, if not, cooling down when bring a warm camera and / or lens outdoors at night will condense water vapor.

SRHelicity:

--- Quote from: Mt Spokane Photography on August 21, 2012, 12:04:19 AM ---Presumably you let the camera and lens cool down for a few hours first?, if not, cooling down when bring a warm camera and / or lens outdoors at night will condense water vapor.

--- End quote ---

It matters what the environment is (I'm a meteorologist, so I hope I can contribute something since I've gained so much photography knowledge from this site).  If it feels really "humid" or muggy, then cooling down the equipment is going to present significant problems.  If the dewpoint is above the temperature of the lens and camera equipment, then dew is going to form on the lens.  This can happen (and has happened to me), for example, if you put your camera equipment in your air conditioned car to drive to your photo location before taking it out into a high-dewpoint environment.  In this case, your lens will be analogous to a cold glass of water on a humid summer day.

I suppose it may be possible to have the opposite situation occur. If you change lenses in a humid environment (by "humid" I mean one with a high dewpoint temperature), you may have issues if you move outside into a cold environment. The camera equipment may cool enough to lead to condensation on the rear element as the "humid" air trapped beyond the lens cools.  This doesn't seem very likely, though, unless the mount and camera is air tight to prevent the "humid' air from leaving the camera / let the drier/cooler air from entering the camera.

I don't have much advice for the OP since I haven't run into this problem.  Actually, if the cause is from a cold lens/camera on a high-dewpoint night, then yes, I have experience this.  I tried to shoot some 4th of July fireworks pictures a couple of years ago when the dewpoint temperature was near 80 degrees.  Since my camera equipment is stored in my house (which was around 75 degrees) and I used AC in my car to drive to the photo location, the temperature of the lens was less than the dewpoint temperature of the outside air. As a result, condensation deposited on the lens, and I ended up with a worthless, hazy photo session.

If this is the cause, then I suggest trying to heat up the equipment in your vehicle first. For example, set the lens on the dash and blast heat from the windshield defroster. This will limit condensation, at least until the equipment cools down to the ambient air temperature (it's not uncommon for relative humidity to reach 100% at night under clear skies, when radiational cooling allows the temperature to cool to the dewpoint temperature). .

risc32:
i usually keep my gear in an air conditioned environment, and leave a window open or 1/2 open during the drive to my shooting location to try and level out the temperature of my gear to the outside air. Maybe it wasn't given enough time. I thought i had a better understanding of this, but after a little google search i just got confused so i thought i'd post my question here. Some of the stuff i was reading said the gear needed to me warmer, some said colder, some talked about how the gear was getting cold because the lens was aimed into space, and it's cold in space. don't aim it there until you really need to, well that doesn't seem practical.  Make a huge lens hood to protect it from the cold, then something about empty fields and trees... anyway, thanks for the info, it's really cool how one can go on the net ask a question and get info back from others who've done what i'm trying to do and actual meteorologists. thanks.

TrumpetPower!:
As Wikipedia puts it, the dew point is the temperature below which the water vapor in a volume of humid air at a constant barometric pressure will condense into liquid water. Condensed water is called dew when it forms on a solid surface.

So, all you need to do to prevent condensation on your gear is to keep it warmer than the dew point.

In most environmental conditions, that's not a problem. However, when the air temperature is below the dew point, you're going to have to heat your equipment to prevent condensation from forming.

I haven't had to deal with this, myself, but I've heard that portable hand warmers are popular amongst astrophotographers for this sort of thing. You might think of wrapping the camera and lens in a blanket and tossing in a low-power electric hand warmer, for example.

Probably the best option is to do your astrophotography in a high altitude desert environment such as Mana Kea, Chile, or Flagstaff. That, of course, can pose different logistical problems....

Cheers,

b&

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