Dew shields and/or heaters?

[abberation]

At least with this cloudy weather you have the time to prepare for the better times. I eventually got round to fitting some Bobs Knobs, made a new observing area in the middle of the lawn which I share with a stone ornament which was part of the deal and I'm in the process of making an outside insulated, vented secure store but more on that later.

I got myself a "sleepig mat" to make a dew shield for the tube and the bits left over were used for the spotter and eyepiece, but reading around I see many folk use dew zappers/heaters. I would appreciate feed back from dob users on what they use. I have read about heaters for the secondary but didn't really want to go down that route. Have considered a 12v heater /blower but would be interested to know what others use.

Richf

[Mr Flibble]

I made one of these for my eyepieces. I also adapted it to include a resister to heat the telrad as well. I power it from a 6v lead acid battery and it works a treat in heavy dew - not had an observing session cut short from dew since.

[NGC 1502]

Sounds like you are talking about dew prevention with the Dobs in your equipment list.

I've only very rarely had the primary mirror in mine dew up, but it can happen.

The main problem with dewing has been with the secondary. Probably the ideal is a secondary heater. But what I use is a camping mat foam dewshield like you have done.

If there is a hint of dew the dewshield goes on, and most of the time works fine. Occasionally the secondary does dew up, then I use a 12v "hairdryer" pointed down the focuser towards the secondary. Works well. But that will only work for light dewing, if the secondary gets sopping wet, the 12v gun is not enough, so I never let it get to that stage. Light dewing significantly dims the view and is a warning to what's happening, so out with the gun quickly.

Some say that using this method is a temporary fix, but it usually lasts for quite a while for me.

Some sort of cover for the finder between uses is a good idea too.

Regards, Ed.

[abberation]

David and Ed - many thanks for the replies - both very helpfull. I have never relly experienced dew problems so far being a newcomer, but looking at the car some mornings has focussed my mind on it.

Richf

[swamp thing]

Hi Rich

I seem to be very lucky with my 10" Dob the sonotube OTA seems to insulate it very well and in the four or so years I've had it, it's dewed up once, that was only the secondary.

On the other hand my 16" Dob was a dew magnet and I never went out without a dew shield, a secondary heater and a 12v hair dryer, so it would seem a lot depends on your individual scopes requirements.

[abberation]

Thanks for that Steve, I think I'll get myself a 12v hairdryer just for fear!

Rich