Non-WR zoom in mist/fog

Started 5 months ago | Discussions thread
norjens Regular Member • Posts: 392
Air is a sponge

When it gets cold it can't hold as much water, and the excess is pressed ('condensed') out of the air sponge. When it gets warmer it can hold more, and absorbs water back into itself, from mist droplets first and then from its surroundings.

If your lens is colder than the air then air gets cooled down as it enters the lens, and forced to shed the water it can't hold at the lower temperature. On the flip side, air pulls water back out of the lens once temperature balance is restored - unless it's already saturated which it is when you can see mist.

Depending on the mist, it may shed water in your lens even if it's the same temperature, but then you will see it happening on the outside as well. Warm the lens up, and the surrounding air will absorb water instead of shedding it on your lens.

The biggest risk from mist or condensation is when it isn't absorbed back out later; for example if formed droplets run down to accumulate somewhere, or if a zoom operation seals of a wet area before it is dried out.

Best practice, WR or not, is to let a lens dry after use in mist or any significant temperature changes, then flip and zoom to the other end to dry out the missed spots.

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