Q & A Truss tube info

[Paddy de Klerk]

Hello,
Would appreciate info from more experienced gazers than myself re;ideal placement of dew heaters on open tube assemblies.For the secondary would a "sock type" heater suffice .being open to the elements at the primary end is the top rim the preferred spot.Is it a no no to consider a fan assisted heater?
Regarding a light shade for the same can one use ,in building parlance,Forticon,or should I avoid this plastic type stuff.A Dew Buster controller would be used for regulating whatever method recommended.A 12 inch Lightbridge being the subject.New moon is close too.Cheers Paddy

[tnott]

I have not actually used the Kendrick type controllers with the various attachments, so can't help you there, sorry.

For my home-built open type newtonian dobs, I have used just the Astrosystems Dewguard on the secondary mirror.

This handy device is siliconed to the back of the glass and automatically senses both the glass and ambient tempereature, only putting in enough heat to keep the dew off.

I keep the fan running to keep the dew off the primary in the 10 inch. With glass much more than 1 inch thick, bigger primary mirrors very rarely dew though, as the glass normally lags behind the ambient temperature as it descends during the course of the night.

I have been next to a solid tube 12" scope whose mirror was totally dewed up with my open 16", 1.5" thick mirror dew free all night long.

I keep the dew off the Telrad by keeping the dewshield in place when not actually finding something.

I keep the dew off the eyepieces by regularly swapping them over.

These stategies have always been enough to keep me dew-free for viewing nights, but I live in Adelaide not Darwin.

[Paddy de Klerk]

Greetings Tknott,it seems like a long time back that I posted my inquiry,Earth time ie.Anyway finally got around to taking your welcome avice &installed heater on the secondry.Got to use it for the first time last night (its been a non viewing few months for one reason only).Worked a treat it did as it was pretty dewy in Sydney.Thanks for the guidance. Paddy