From the February 2010 issue

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
By | Published: February 22, 2010 | Last updated on May 18, 2023

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.