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Webster Telescopes Forum • View topic - dew prevention on C18 primary mirror
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 Post subject: dew prevention on C18 primary mirror
PostPosted: Fri Jul 12, 2013 1:19 pm 
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Joined: Sat Sep 15, 2012 7:33 pm
Posts: 3
I have a C18 scope, Zambuto F/4 and about to order a "{dew buster" controller and "dew-not" heater strips (provide a very uniform heat). I am interested in any comments on how best to prevent dew on this size primary. I see the dew-nots are built up to 16 inch. I am considering also how to attach given the cable sling mirror support. Will also ask the dew-not folks. I might need two narrow strips so I can wrap the mirror on both sides of the cable sling on the circumference of the mirror.
As a second option, I have a 12 volt "hair dryer" blower that can gently shoot slightly warm air toward the mirror surface (that I could mount to a truss). This would be used for quick dew-removal; but may also work as the primary dew preventer (instead of dew-not strips) if left operating at low enough rate to keep mirror surface just a few degrees above ambient.

Thanks. Al DenBleyker in Waimea, the Big Island near Mauna Kea


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 Post subject: Re: dew prevention on C18 primary mirror
PostPosted: Thu Jul 18, 2013 11:33 pm 
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Joined: Thu Jul 02, 2009 11:48 am
Posts: 80
Location: Detroit Michigan
A primary of that size might get dewed over once every 2 years.

The only time that can happen is when the night air suddenly increases in temperature so fast that the cold mirror becomes covered in condensation.

Obviously, this happens very rarely (only on nights with fog in MI).

The one place I see a real use for Dew prevention on the primary is when camping overnight. Once you are done observing, crank up your Dewbuster and that will keep condensation from forming in the 8am - 11am "morning dew zone".

Aiming the back end of the scope towards the sunrise can also help with morning dew.

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Eric Webster
http://www.WebsterTelescopes.com


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