Dew Heaters

[M4lcs67]

Hi Folks, As the cold, dark nights approach I have been thinking ahead and contemplating getting a dew heater, but was wondering if anyone thinks they are a good idea/a necessity? I already have an Astrozap Dew Shield, but have not had a reason to us it so far. I assume I would need some kind of splitter for my powertank as well so I can power the scope and dew heater at the same time?

Thanks in anticipation

[brantuk]

Hi Malc - when the atmosphere is moist then a dew heater is allmost mandatory. Refractor objectives will mist up, relfector secondaries are prone (dew shield helps), and Sct's / Mak's loose the corrector.

Most power tanks have two ciggy lighter sockets, if your's only has one then a splitter will do the job, but a dew system will drain it quick. You'd need to work out how long you want for a session, what the battery characteristics are (amp hours, volts, etc), and get a pack that will last the duration with the calculated loading.

I use 17ah to drive my scopes, but for heater systems I use a 240v/12vdc adaptor and run it off mains (at home) or EHU (campsites). Leisure batteries are good out in the field with no mains supply. You can get 70ah's starting at about £60.

[M4lcs67]

Hey Brantuk, Thanks for the useful info again. I suppose I would be well advised to try the scope with either nothing on or put the dew shield on and see how it goes before going and buying a heater? Just been on the FLO website and they are rather costly when you think that you need the heater tape and controller. To be fair I would have thought that if you are outside in the middle of winter with a clear sky there would not be much excess moisture in the air? Well what do I know! This is my first winter season, so a perfect chance to hopefully hone my skills/knowledge. My powertank is one of the Maplin 3 into 1's and only has one cigar lighter socket, but I do have an external wall socket on the back of my house about 30 feet from where I set the scope up.

[MorningMajor]

To be fair I would have thought that if you are outside in the middle of winter with a clear sky there would not be much excess moisture in the air?

Sadly, there's plenty of moisture around, even on clear winter nights - just check you car windscreen every morning! That said, I faired quite well last winter with just my home made dew shield (same scope as you) and didn't have many evenings curtailed by dew - the cold though - that's another matter!!

[JamesM]

If you should decide eventually to get yourself a dew strip, I would recommend the 'Dew-Not' brand from the US as it transfers the heat via a gel rather than a heating element and therefore is both more effective and more efficient than the normal strip, therefore reducing the amount of power that is used.

James

[brantuk]

I allways put a dew shield on cos even if there's no dew, it blocks stray light reflections from the sides that will otherwise reduce contrast. If the dew is light then you may get away with occasional use of a hair drier blown gently on low heat round the shield every 30/45 mins or so.

Don't blow directly on the optics in the cold or you might risk cracking the a lens or corrector plate. But really, as the Major says above, dew is around even on clear winter nights. I like the sound of "dew-not" - never tried them but the gel thing sounds sensible