Lens Warmer

Started 5 months ago | Discussions thread
Michael Fryd
Michael Fryd Veteran Member • Posts: 7,743
Re: Lens Warmer

CameraCarl wrote:

When you take cool gear into a warm humid place (such as from an air conditioned room into humid Florida weather) or from a warm humid place (such as your Car) into the cold you will get condensation ...

You don't get condensation when going from a warm place to a cold place.  You only get condensation on an object when that object is colder than the dew point of the surrounding air.

This is why its common to see condensation on a glass filled with an ice cold drink, but you don't get condensation on a hot cup of coffee.

I've shot birds in minus 20 degree Fahrenheit conditions without needing any supplemental stuff like heat packs (except for the ones for my hands).

Correct.  In order to get condensation in -20°F conditions, you would need to have the camera even colder than that.    Your camera was probably much warmer than the -20°F ambient air, and therefore not in danger from condensation.

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Science background:

The amount of water that air can hold is dependent on temperature.  Warmer air can hold more water.

The amount of water that is in the air relative to the air's capacity id the "relative humidity".  This is what people generally mean when they talk about humidity.

As you cool air, the absolute amount of water in the air stays the same, but the relative humidity goes up.  This is because cold air can hold less water so the ratio of water that's there to the what can be held goes up.

At some point the air gets cold enough that the amount of water it can hold is equal to the amount it has.  This is the "dew point", and the relative humidity is 100%.  Any colder than this and you see condensation.

When you take a cold camera outside, the warm air that touches the camera gets cooled.  If it is cooled down past the dew point, you get condensation on the camera.

When you put the cold camera in a plastic bag and take it outside to the heat, the air in the bag warms a bit (warming won't produce condensation).  The air outside the bag cools a little bit.  If you get condensation on the outside of the bag, the bag keeps the water off the camera.

Once the camera is warm, you can open the bag.  The higher outside humidity won't be a problem as long as the camera has warmed past the dew point.

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