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Is it normal for telescope optics to freeze up when the temperature is below freezing with high humidity? If so, how can I prevent this?

William Jones, Naperville, Illinois
Thousand Oaks Optical’s Digital Dew Heater Control Unit
Thousand Oaks Optical’s Digital Dew Heater Control Unit features 4-channel operation and a battery-saver function.
Astronomy: William Zuback
The best way to avoid dew — or ice — on optics is to use a dew heater.

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