Dew Problems

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Dew Problems

Post by cmcdougall » Wed Oct 10, 2012 9:54 am

Having bought a bigger telescope, I have for the first time encountered dew problems. I used a hair drier to keep it clear for the time I was attempting to image Jupiter, but then was told off by my wife for having her hair drier out in the damp!

I am a bit self-conscious about buying my 'own' hair drier, so would like to hear how other members have gone about dealing with this problem. I have seen a few dew heaters online but am unsure about what sort is best and indeed if there are any other DIY (very simple!) solutions that don't necessitate too much cash outlay.

I was also told that electrical heaters can be detrimental to imaging, since they create small distortions. Is this the case?

Thanks in advance,


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Re: Dew Problems

Post by rwilkinson » Wed Oct 10, 2012 10:29 am

See this thread: ... p?f=6&t=11
The 12v hair-dryers are certainly safer outside than their mains counterparts, but prevention is always better than cure, so fit a (cardboard?) dew-shield around your tube (and finder-scope) and in extreme cases consider fitting some electrical heating tapes as per Dave's design.
You can also fit a tape around your eyepiece (if you can get one big enough ;) )

The idea is to keep the optical surfaces just a little warmer than the ambient air, so use a controller to regulate the power supply - see Ian's recent post: ... 366&p=1345

Or Gerald has found that with a simple (cold-air) desk fan keeping the air moving around the telescopes in his observatory he doesn't get any dewing, but this may not work so well out in the open?

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