A dew heater is an electronic device used in astronomy to prevent the buildup of moisture on lenses, mirrors, and other optical surfaces. When observing or photographing celestial objects, temperature changes can cause water vapor to condense on the surface of optical elements, leading to reduced image quality and potentially damaging the equipment over time.

Dew heaters work by using a heating element, typically a thin strip or pad of resistive material, that is placed in contact with the optical surface. The heating element is connected to a power source, such as a battery or AC adapter, and is controlled by a thermostat or other temperature control system.

By warming the surface of the optics, the dew heater raises the temperature of the optical elements slightly above the dew point, preventing moisture from condensing on the surface. This helps to maintain clear, sharp images and prolongs the life of the equipment.

Dew heaters are available in a variety of sizes and configurations to fit different types of telescopes, cameras, and other optical equipment. Some dew heaters may also include additional features such as temperature sensors, adjustable thermostats, or battery packs for portable use.