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I live in Florida and I'm trying to shoot some star trails, but condensation keeps fogging up my lens. 1) Does using anti-condensation coating work and 2) Will it harm the lens? I've read that you should warm the lens, which makes sense, but that seems difficult. I think there may be some sort of coating already on the lens, I'm not sure. (Shooting on the a6300 with the 16-50mm F3.5-5.6 kit lens)

  • I thought condensation happens when you take cold equipment into a warm room. But it sounds like you are having problems with condensation outdoors - am I understand the situation correctly? – Nayuki Feb 20 '17 at 0:46
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    Condensation can happen in environments with high humidity and clear skies. The lens/telescope/grass/car etc. loses heat to the clear sky via radiative losses (you generally don't get dew when it's overcast) and moisture condenses on the item. @DrMoishe Pippik's suggestion to use a lens heater is a good one. You don't need much heat, just enough to keep the lens above the dew point. – BobT Feb 20 '17 at 3:48
  • @BobT As an astronomer, I'd recommend against heating elements, as they will lead to local thermal drafts and possible image distortion. Granted, for lenses less than 6 inches diameter, not likely to be a huge problem, but all the same better to let all equipment sit outdoors until at thermal equilibrium with the surroundings. – Carl Witthoft Feb 20 '17 at 14:04
  • I generally agree that heating has to be done in moderation. As I said, radiative loss can cool the front element (among other things) below the dew point. One only needs to keep the front lens element slightly warmer to prevent condensation. – BobT Feb 20 '17 at 14:45
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Keep the lens as clean as possible as dust and dirt become the nucleus that forms condensation. Best is Zeiss cleaning pads now on sale at WalMart optical department and other such stores. These consist of lens cleaning solution (ethyl alcohol) on soft lens tissue. After cleaning, make a weak solution of five drops of baby shampoo in a cup of distilled water. Apply this to the lens by wetting a well washed and clean "T" shirt with this solution. You are to apply a thin film. This is a scuba divers trick and it works. It will not harm babies and it will not harm your lens.

  • A "t-shirt" is not a quantifiably valid cloth description. I would recommend using lint-free optical wipes. – Carl Witthoft Feb 20 '17 at 14:05
  • A well washed "T" shirt is commonly used when assembling precision lenses in an optical shop. This material when saturated with ethyl alcohol is one of the best. In my youth I made lenses for enlargers. We encouraged employees to bring it their old washed "T" shirts. – Alan Marcus Feb 20 '17 at 17:35
  • Well, over at the companies where we assembled both high-power laser optics and precision optics for adaptive optic systems, a filament-shedding material such as cotton would never be allowed. – Carl Witthoft Feb 20 '17 at 18:09
  • I have lens tissue paper, I think that should work. – Max Feb 20 '17 at 21:55
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    It's the ethyl alcohol that is the key to getting the glass surface clean. the Zeiss cleaning pads are ideal. You can use vodka, it's ethyl alcohol. You are cleaning the surface of the lens, not assembling. A well washed "T" shirt is absorbent and lint free. The "T" shirt idea is best for in-the-field cleaning. The vodka can be used for other purposes as well. – Alan Marcus Feb 20 '17 at 22:10
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I also live in Florida and shooting night baseball games in the summer can be a real trial. Big glass can take 30-45 minutes to fully acclimate. But that is the real solution - acclimation: if you plan to go out at night, put your equipment out mid-day in a garage (or other location out of the sun) and let it acclimate. Leave lens/body caps on, and if coming from AC (i.e. really cool comparatively) leave it in the case so it warms slowly (more to the point so hot humid air gets to it slowly and does not condense right then).

This is not a 100% solution as some nights here the relative humidity is so high everything gets moist, but it will get you close. A sun shade is also a good idea to keep descending moisture from it, if shooting more horizontally (but not much good shooting up, obviously). I usually put my gear in the car (in a garage) the morning before a game, give it all day to warm.

If you are near power, a hair dryer at a distance to evaporate gently any dew that falls and warm the front element slightly can also help; do not get it very warm - just a few degrees warmer than ambient (or see the heater mentioned below).

Minimize lens changes in this environment, as the rear elements and even camera internals also tend to get a damp coating (the same hair dryer -- at a distance -- will heap there if you must change, get a bit of warm, dry air inside first). Be sure all lenses and other accessories you may use are acclimated as well.

Never use canned air or any pressurized similar product to blow off/dry the lens, as that air is much cooler than ambient due to the pressure change; its cooling effect on the glass will make the situation worse.

I would avoid any treatments for optics reasons (not so much damage as clarity). Do not wipe dew-dampened lenses, ever - dust on the lens, now wet, will scratch (and because it is wet you cannot use the usual solution of a brush or blower). They must dry/warm over time. Do not be tempted to wipe "just that last bit of dew" off. Wait.

When done and back inside, leave the cameras out of the case and let them dry in the dry air inside an air conditioned environment. If there was enough dew to leave scum behind, clean it then, not in the field (usually dew is near pure water and evaporates cleanly, well, if you didn't mess with it trying to wipe it off).

Please do not take any comments above to imply you need to get the lens hot. Optics work best if they are at a stable temperature near air temperature. If you go the hair dryer route, do it VERY gently.

  • Should I use a lens hood? (Following the logic of the sunshade.) – Max Feb 20 '17 at 21:58
  • Lens hood/sunshade, same thing - if you are aiming up it will make no difference, but if more horizontal it may help. Some moisture is condensing simply from the air, and makes no difference. Some is condensing IN the air and falling as extremely tiny drops, like rain but almost floating - those are helped by a lens hood if it is vertically above the lens. – Linwood Feb 21 '17 at 0:13
  • Careful with that comment about dust. Dust is less likely to cause damage when wiped away wet than when wiped away dry, not more likely. Obviously, it is safer to blow it away while dry, of course, and when you're talking about sand, that's probably a much, much better idea than wiping it. However, a soft brush can work reasonably well if dust is stuck and won't come off by blotting with a damp cloth. – dgatwood Feb 25 '17 at 21:49
  • The issue of course is whether, when you have a wet mess, you know if the dust in it is lint or soft items, or grit that can scratch. I just consider it better to assume particulate matter can scratch, brush/blow it off, and clean any that remains with a cloth if necessary afterwards. Probably depends where you are as well. Remember in Florida (as the OP said), there's a lot of sand, rock dust, grid, silt, mud.... so I may have a different starting point than those living in less gritty areas. – Linwood Feb 26 '17 at 4:03
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I would not put anything (other than perhaps a tiny amount of high-quality lens-cleaning solution on lens tissue) directly on a camera lens, as it may damage the coating or even seep into the lens barrel. The anti-reflective coating depends on interference effects in very thin films, on the order of a fraction of a wavelength of light, and some of these coatings are porous. If you get a smudge on a coated lens, you will notice a black or shiny spot that is almost impossible to remove.

If you'd like to experiment, use an inexpensive, uncoated clear or skylight filter with the anti-condensation glop, but my experience has been that the coating is not very effective, whether on glasses or goggles.

A better solution is a lens/filter heater, e.g. the Dew-Not for ~US$33. You could easily fabricate your own with resistance wire and a bit of ingenuity. See Phil Hart's discussion of dew heaters.

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    Almost certainly is pretty strong language considering that you don't specify what kind of anything you're talking about. Can you back up your blanked assertion or be a little more specific? – Caleb Feb 20 '17 at 2:21
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    I agree with Caleb, I almost didn't get to the last paragraph, which is indeed an interesting solution, because of the over-emphasis on the fragility of the lens coatings. Sure, you can damage them, but you have to work at it a bit. – Linwood Feb 20 '17 at 15:48
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Check out this discussion from Sky and telescope, which gives two options:

  1. Shielding and
  2. Warming

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