Dew on Newtonian mirror.

[zenofrag]

Hello,

I have a 10" Newtonian in an Orion aluminium tube. I am finding that the mirror dews up very easily. It is a full thickness mirror. Does anyone know of a solution to this problem ? The secondaty also dews up but I am able to clear this with a hairdryer. Both the flat and main mirror are very close to the end of the tube.

many thanks for any advice you can offer.

[eliot]

I have the same issue and haven't really been able to solve it either.

I have used a hair dryer to heat the primary mirror from the rear it takes a minute or so. I haven't noticed any tube currents myself, but I'm not convinced that this is the best method.

The other way I have read about is to put a PC fan on the primary. This apparently helps by moving the air around the mirror stopping it from forming dew.

[perfrej]

Folks, you may want to read my total rant about dew formation here: http://stargazerslounge.com/discussions-scopes-whole-setups/159256-do-reflectors-need-dew-shields.html#post1982389

All the best,

Per

[NGC 1502]

My main scope is a 10" Dob. I've only had the primary mirror dew up a couple of times (yes I do use the scope on sub-zero nights) If that happens a lot, then as suggested a PC fan blowing gently on the mirror from below should keep the air moving and lessen the problem.

The secondary has dewed up more frequently, so I use a camping foam dew shield extending about 12" from the upper end of the tube, and on rare occasions use a 12v dew gun pointing down the focuser. As the secondary is about 6" from the end of the tube (and pointing down) this means that the upper end of the dewshield is about 18" from the secondary.

Regards, Ed.