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



## risc32 (Aug 21, 2012)

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 (Aug 21, 2012)

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 (Aug 21, 2012)

Mt Spokane Photography said:


> 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.



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 (Aug 22, 2012)

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! (Aug 22, 2012)

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&


----------



## SiliconVoid (Aug 22, 2012)

For some reason I have not had too much problem with lens sweating since using digital, maybe due to the sensor heating up or something (a guess, heh) but back in the film days we would heat a leather belt (like holding it up to your exhaust pipe) and then wrap it around the lens.. Today you could probably get some of those little packs you put in your pocket in the winter and slip a layer into a sock or something and wrap it around the lens.


----------



## Ryan708 (Aug 22, 2012)

It has been humid as the jungle lately here in the new england area. My lens fogs up once the grass starts to get morning dew. Only a fairly warm lens will not condensate on nights like we have been having.


----------



## bbasiaga (Aug 22, 2012)

Another thing toconsider is the black body radiation of your gear after dark. If the temp gets close to the dew point, your gear will drop just a fractionbelow as it radiates a very small part of its heat off in to space. As an astrophotographer myself, Ihave run in to dew problems myself. To combat it, the most fool prof thing is to vet some dew heaters, basically a fancier version of the hot pads mentioned above. Astrozap is a companythat used to make them. Serch around and youlk find a few options. If you turn them on at the start of your session they keep you from getting close to or below the dew point. 

Another thing would be to use your lens hood, Those who use telescopes tend to use dew shields which arebasically hoods ffor telescopes. They keep the air next to the objective stagnant and therefore pdevent it from cooling down as fast. They also reduce the radiation heat loss. With telescopes the light cone is very steep and therefore the hood can be longer, but your lens hood should help some. 

-Brian


----------



## daniel-barton (Aug 22, 2012)

I have used chemical handwarmers and gaffer tape to warm battery grips and lenses when shooting football in cold weather, and stuck them in my bag to keep gear a hair warmer. You can gaffer them to a lens too, but stick some insulation in between/around them because they do get quite hot (yet one type of chemical heater still needs oxygen to produce heat, so airflow is required as well). I sometimes use an AquaTech - *love* mine - and that seems to provide enough insulation. I don't think it would be a great idea to get a lens very asymmetrically hot with one of these handwarmers, but you know, I doubt it matters with the quality of construction on an L lens. I have done this for a long exposure only once, but same idea.

Here's a diy instruction thread on how to make an electric heater:

http://photography-on-the.net/forum/showthread.php?t=363744

Hopefully this is of use.


----------



## Mt Spokane Photography (Aug 22, 2012)

For astro photography, you want a cold sensor, the colder the better, since there is less noise in long exposures. Advice to heat a camera for astrophotography seems to me to be going the wrong way. The vapor will clear out after a few hours.


----------



## TexPhoto (Aug 22, 2012)

I live in the Caribbean, and humity and condensation are constantly a problem. Some techniques we use are heat the cameras front lens with the cars heater. Leave the camera bag outside to get used to the temperature outside before your remove the camera. Don't bring the camera into an air conditioned car or room, but if you must, put it in a cooler ( they keep things warm too)


----------

