Dew Heater / Dew Shield, Inside Observatory?

[Benjam]

Hello SGL members, I’m new to this forum and to the hobby. 

 

I have always been fascinated in the moon, stars and deep space and would always try and watch Sky At Night, but that was as far as my interest went.

2018, I spent sometime in the Australian Red Centre, sleeping under the stars, I was totally blown away.  Seeing the Milky Way for the first time really inspired me to actually do something about it. I did the Sydney Observatory Tour ASAP and had my first look through a Telescope. Returned home to Blighty earlier this year and brought my first scope (8 Edge HD). Loved the hobby so much that I’ve just installed a 2.2 Full Hight Pulsar Dome. 

Anyway my question is....  

I was wondering if SGL members use or think its necessary to use Dew Heaters / Dew Shields whilst inside a Dome Observatory?  

My logic was, I’ve already got it, so might as well use it. I can’t see it doing any harm.

 

Ben 

[Thor92]

I'm fairly new to all this, so I could be wrong.
However I am a marine engineer and my inner engineer says that yes it is absolutely still needed.
Unless you have the entire telescope in a sealed environmentally controlled room ( I doubt your dome is ) your still going to get dew. So your initial instinct is correct (In my opinion) keep using it  
Hope that helps somewhat.
PS- I'd be interested to see pictures of your dome. Always liked that idea!

[steppenwolf]

I tend to think of my observatory dome roof as being a 'sacrificial dew-catcher' so I don't ever use a dew heater from within the dome. I have yet to find dew on my primary lens in any conditions - however, outside the observatory is a very different situation!!

[andrew s]

I think it depends on the atmosphere inside the dome. If the temperature is below the dewpoint for the dome atmosphere on any surface in the dome then dew will form on it. If you go to the trouble to ensure the dome is close to the night time conditions for good seeing then dew will be more likely .

Regards Andrew 

[Skipper Billy]

My observatory is the open roof type rather than a dome and for me dew bands on imaging scope and guide scope are absolutely essential.

 

[Hawksmoor]

My old architectural practice was multidisciplinary (including mechanical, electrical and environmental engineers) and we designed a number of archive facilities which had strict environmental controls  regarding relative humidity and temperature.  I have some experience , some success and more than a few set backs in battles with condensation.

The key issues are the relative humidity of the air and the surface temperature of your kit. In my backyard where I observe the relative humidity is often somewhere between 85 and 95% at this time of year. As soon as I take out my scope or cameras they start to radiate heat out into space. At some point in time the glass will cool and reach the dew point (the temperature at which the moisture in the air can no longer exist as a vapour). Irrespective of the amount of thermal insulation or the thermal mass of the glass at some point in time the dew point will be reached and condensate will appear where I don't want it. Thermal collars and the like which I have made delay the inevitable for about a hour and a half for the smaller bits of glass (camera lenses, my 66mm refractor and 60mm guide scope) and approximately 3 to four hours for my 127mm refractor's objective lens. The only way to prevent this happening is to add back the heat (that is being lost through radiation out into space) either by using a hair drier or dew heaters.  For this reason I have just made dew heaters for all my bits of kit as I got fed up with having to stop imaging on the few clear moonless nights available because 'Niagara Falls' had turned points of starlight into fuzz balls. I suspect your 'observatory enclosure' will increase the time before the dew point is reached but if the relative humidity of the air in the observatory is high and in reality it will be similar to ambient external RH, condensation will eventually form on bits of kit that have a surface temperatures equal or lower than the dew point temperature.

I've rambled on for a bit - sorry - old consultants never die they just ramble on for a bit more.😀

best regards from George 'moist' in Lowestoft next the Sea.

[Benjam]

3 hours ago, Thor92 said:

PS- I'd be interested to see pictures of your dome. Always liked that idea!

Thor92 - I’ve been taking pictures throughout the project. I will definitely post a build thread, when finished. It’s the small little jobs that take more time then you initially realise. 

I soon realised after setting up  / taking down my scope, each session was becoming a chore. Especially the taking down part, hence the observatory. 

 

Ben 

[Benjam]

3 hours ago, steppenwolf said:

I tend to think of my observatory dome roof as being a 'sacrificial dew-catcher' so I don't ever use a dew heater from within the dome. I have yet to find dew on my primary lens in any conditions - however, outside the observatory is a very different situation!!

Thank’s Steve, that makes sense. I’m going to monitor the situation, with and without. I live within spitting distance of the River Avon and wonder if that has a impact on the local moisture levels. 

I did however setup a dehumidifier today, to drain away constantly. 

 

Ben 

[Benjam]

3 hours ago, andrew s said:

I think it depends on the atmosphere inside the dome. If the temperature is below the dewpoint for the dome atmosphere on any surface in the dome then dew will form on it. If you go to the trouble to ensure the dome is close to the night time conditions for good seeing then dew will be more likely .

Regards Andrew 

Thanks Andrew. I’m running a dehumidifier as from today. I guess I turn off the dehumidifier when I have the shutter open to the elements? 

 

Ben 

[Benjam]

2 hours ago, Skipper Billy said:

My observatory is the open roof type rather than a dome and for me dew bands on imaging scope and guide scope are absolutely essential.

 

That’s a nice looking Observatory Billy. Did you build that yourself? I’m a chippy by trade, so always interested in construction. 

 

Ben  

[steppenwolf]

10 minutes ago, Benjam said:

I did however setup a dehumidifier today, to drain away constantly.

I have my dehumidifier running all the time that I am not actually imaging and it has kept my gear in perfect condition for years.

[Benjam]

2 hours ago, Hawksmoor said:

My old architectural practice was multidisciplinary (including mechanical, electrical and environmental engineers) and we designed a number of archive facilities which had strict environmental controls  regarding relative humidity and temperature.  I have some experience , some success and more than a few set backs in battles with condensation.

The key issues are the relative humidity of the air and the surface temperature of your kit. In my backyard where I observe the relative humidity is often somewhere between 85 and 95% at this time of year. As soon as I take out my scope or cameras they start to radiate heat out into space. At some point in time the glass will cool and reach the dew point (the temperature at which the moisture in the air can no longer exist as a vapour). Irrespective of the amount of thermal insulation or the thermal mass of the glass at some point in time the dew point will be reached and condensate will appear where I don't want it. Thermal collars and the like which I have made delay the inevitable for about a hour and a half for the smaller bits of glass (camera lenses, my 66mm refractor and 60mm guide scope) and approximately 3 to four hours for my 127mm refractor's objective lens. The only way to prevent this happening is to add back the heat (that is being lost through radiation out into space) either by using a hair drier or dew heaters.  For this reason I have just made dew heaters for all my bits of kit as I got fed up with having to stop imaging on the few clear moonless nights available because 'Niagara Falls' had turned points of starlight into fuzz balls. I suspect your 'observatory enclosure' will increase the time before the dew point is reached but if the relative humidity of the air in the observatory is high and in reality it will be similar to ambient external RH, condensation will eventually form on bits of kit that have a surface temperatures equal or lower than the dew point temperature.

I've rambled on for a bit - sorry - old consultants never die they just ramble on for a bit more.😀

best regards from George 'moist' in Lowestoft next the Sea.

George, I could listen all day. You’ve convinced me. I just need to custom make a shelf on my pier to allow for my Nevada PSW-30 25 Amp Mains Power Supply  . 

 

Ben 

Edited September 29, 2019 by Benjam