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Dew Heaters for large truss dobsonian?

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#1 Gschnettler

Gschnettler

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Posted Yesterday, 08:00 AM

What kind of dew shields or heaters are typically required for 12” or 14” truss style dobsonians? Do you need two - one for the top mirror and one for the primary mirror? How would you mount them?

#2 Junoscope

Junoscope

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Posted Yesterday, 07:42 PM

The mirror box and shroud can keep drew off of the primary mirror.  The primary will usually need to be cooled by a fan or fans.  If you bring outside from an air conditioned environment, the fan will still help to bring the mirror to ambient temperature.  I don’t live in an overly humid part of the country. 

 

Diagonals can become covered with dew.  I use the simple remedy of a resistor silicone glued to the back of the diagonal. The scope is wired through one of the truss tubes to heat the diagonal, Telrad glass, and Sky Master display. I’d have to check the resistances.  I haven’t noticed any difficulties with the diagonal heat, but more sophisticated setups with thermostats are available.  
 

I rarely have a dew problem with the diagonal where I live.  My upper assembly is a short tube rather than a one of the open, light weight structures. You may want to try your scope first without a diagonal heater if you live in a drier part of the country.  




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