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I have recently upgraded from a Reflector to a CST and I suddenly get this dew problem that I have read about fairly frequently.  I was just wondering if someone could explain to me as if I was an idiot exactly what I need to do to prevent this misting up?

I am currently making a home made dew shield which I understand will give me 30 minutes or so grace, however looking online there are other solutions that are better?  However I am getting confused as to what exactly I need, there seem to be several bits and I am struggling to find a simple "buy X, Y and Z" type instructions.

I am also rather broke at the moment, so even better are there DIY type guides to dew control around?

Many tahnks

Ryan

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The shield will help but somehow you need to add a little heat so the corrector plate is held fractionally above ambient temperature. The minimum amount of heat necessary to do the job, and put in the right place is best - which means applying it to the outside of the tube very close to the edge of the corrector plate itself. That is usually achieved with a strap wrapped around the tube and connected to a variable power output controler.

Yes, there are DIY solutions involving nikchrome wire or a string of resistors wired in series, and if you are competent at a bit of soldering then it can be done. I don't have a link to hand but a google search will throw up many results. You do need to be careful not to use too much heat with a DIY approach as that will degrade the optical performance.

chrisH

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As per above - hairdryer on medium heat to clear any dew already formed, dew controller to drive the band(s), and some bands. Good idea to make a dew shield - use that as well as the bands for best effect. Then if you need to use the hairdryer again you're getting close to session packing up time. :)

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Here's the "why it happens" bit:

http://www.blackwaterskies.co.uk/2013/05/dew-formation-and-prevention.html

Here is everything you need to know to build your own dew heater bands.  Nothing is left to the imagination, full instructions and a spreadsheet to help you design it, shopping list plus illustrated instructions on how to make the thing. It can be done for a few quid if you have access to a soldering iron (and even that can be avoided if you use fishing line crimps).  You do need a basic multi-meter, but that should be pretty easy to borrow if you don't have your own:

http://www.blackwaterskies.co.uk/2013/05/making-your-own-nichrome-dew-heater.html

Here's how to build a dew heater controller for maybe five quid, or perhaps 20-30 quid if you want the 'deluxe' model:

http://www.blackwaterskies.co.uk/2013/05/a-cheap-multi-channel-dew-heater.html

I have been using my heater bands and controller for two years now on both refractors and an SCT.  The wife's hair-dryer misses its midnight outings however.

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The shield will help but somehow you need to add a little heat so the corrector plate is held fractionally above ambient temperature. The minimum amount of heat necessary to do the job, and put in the right place is best - which means applying it to the outside of the tube very close to the edge of the corrector plate itself. That is usually achieved with a strap wrapped around the tube and connected to a variable power output controler.

Yes, there are DIY solutions involving nikchrome wire or a string of resistors wired in series, and if you are competent at a bit of soldering then it can be done. I don't have a link to hand but a google search will throw up many results. You do need to be careful not to use too much heat with a DIY approach as that will degrade the optical performance.

chrisH

resistors wired in parallel  :p 

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resistors wired in parallel  :p

Nope, mine were wired in series so the whole chain of them combined gave the right resistance for the required heat output. :)  They were then threaded into a rubber tube to keep water out, and it worked fine.

ChrisH

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Nope, mine were wired in series so the whole chain of them combined gave the right resistance for the required heat output. :)  They were then threaded into a rubber tube to keep water out, and it worked fine.

ChrisH

right fair enough, but if 1 fails the whole system goes down :smiley:

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