What is a telescope dew shield?

BBC Sky at Night Magazine's Scope Doctor Steve Richards solves your practical astronomy ailments.

A simple dew shield can be constructed using many household items. Read our guide to creating your own here. Credit: Ben Kent

What is a telescope dew shield?

Steve says: “Dew shields are metal or plastic extensions to a telescope’s optical tube. They serve two functions; to stop stray light entering the light path from oblique angles and to help keep dew at bay.

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At first, a telescope cools down via the movement of air until it’s the same temperature as its surroundings.

However, after that, the glass elements continue to radiate heat away, which can cause dew to form.

A dew shield traps a pocket of air in front of the lens, helping to control the rate of this radiation and prevent dew from building up.”

Follow our guide to make your own telescope dew shield.

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Email Steve your astronomy queries to scopedoctor@skyatnightmagazine.com.