Dew prevention for a dob

[WilliamAstro]

How to prevent dew from building up on the external parts of a dob? (e.g. the mount, the casing around the mirror)

[bosun21]

Apart from throwing a sheet over it that is why would you want to? The metal tube will dew over every time the dew point is reached. I have only ever used a standard dew shield to give my secondary some protection on nights of heavy dew. If you are concerned about the primary mirror you can place a shower cap around the primary cell. Just let the scope dry off properly when you are done observing for which I point the tube slightly downward and caps (shower cap) off.