Reflector dew control

[MarkInSpace (Mark)]

In imaging sessions on the Mornington peninsula I’ve had problems with my reflector primary dewing and frosting up.
Last night was especially bad.
I have a Saxon 10” metal reflector OTA. The night started fine but by midnight I had a coating of dew/frost on the secondary and primary mirror. The temp was about 8 when I started but dropped during the evening. I had a homemade dew shield on the top of the telescope, but it did not solve the problem with the primary mirror.
In the end I had to end the session because of the dew issue.
I am buying a heater for the secondary mirror, but not sure about how to solve the problem with the primary.
Would a fan on the back of the primary solve the dew problem?
Is there a different answer?

[astronut (John)]

Hi Mark,
Does your scope have a fan? If yes do you use it?
A dew heater for your secondary will solve the problem.


I use both on my 12" Truss with great success.

[ChrisV (Chris)]

There's a good article on IIS
https://www.iceinspace.com.au/63-771-0-0-1-0.html

And there was a good thread here a few years ago. But can't remember where

[MarkInSpace (Mark)]

Thanks for responding Chris and John
I read the article with interest and attached a fan (blowing out) to the back of the mirror. I’ve also bought a “wrap around” secondary heater.
Let’s see how that goes.
Cheers