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)
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.
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.
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.
Check out this discussion from Sky and telescope, which gives two options:
- Shielding and