Dew forms when your telescope or camera surfaces cool down faster than the surrounding air, dropping below the dew point temperature. This causes water vapor to condense as tiny droplets on cold surfaces like lenses, mirrors, or tripods.
Clear, calm nights with high relative humidity are prime conditions for dew. Early signs include a slight fogging or a subtle wetness on optical surfaces.
Spotting dew early lets you activate dew heaters or dry the optics gently before image quality suffers or damage occurs.
