Moisture condensing as dew on the optics of a telescope can quickly ruin a star-gazing session. Telescope dew protection and removal system can consist of the following components:
Dew Shields and Dew Caps
Dew shields offer "passive" dew protection and are short, black aluminum tubes that fit on the end of a telescope tube. Dew shields come in various diameters and lengths to fit telescopes of different design and manufacture. Dew shields have the added advantage in that they block stray light from entering the telescope by virtue of extending past the end of the telescope tube.
Dew Removal Heat Guns
Anti-dew heat guns look like small hair blowers that operate off a 12V battery or auto cigarette lighter. They are ideal for removing dew right now and where it is needed. Be forewarned however that heat guns can quickly deplete your telescope's battery.
Anti-Dewing Heating Systems
Complete dew removal systems consist of several flexible tape heating elements that attach with velcro to various places on a telescope where dew forms - the objective optics, finder scope, and eyepieces. Also included is a controller is used to adjust the temperature of the individual heating elements. Active dew removal systems are powered off of 12V - it is recommended that you dedicated a spare car battery to power such a system lest your drain your telescope's battery in short order.
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