Dew !!!

[Skipper Billy]

I stay right by the sea in a glen and whilst the dark skies are superb the dampness and dew is horrendous.

What's the best solution ??

Try to prevent dew forming by having a dew shroud, or using a heater strip/band or both ???

I use a large leisure battery for laptop etc so power isn't a problem.

The two scopes that need something are both Skywatchers - an ED80 and a 200PDS

Any advice most welcome!!!

[Dreadz]

I'm in a fairly similar situation. I live pretty close to an estuary and I have found there's only so much my home made dew shield can do so dew heaters are on the list of must haves for me. Try a dew shield see how it goes, you can make one youself for a couple of pounds out of a camping mat, if that doesn't do it add some heaters

Sent from my GTi9300 using random spelling mistake generator!!!!

[Bizibilder]

Dew forms when saturated air comes into contact with a surface that is below the dew point (colder than the air).  The solution is to warm the optics up and keep them above the dew point.  The trouble is that the DP is a moving target and can change with temperature (warm air can "hold" more water vapour than "cool" air).  By warm I mean that the optics have only to be a degree or two above the dew point - not warm to the touch!!

Dew shields simply stop the optics radiating heat away and thus self-cooling themselves - dew will still form as soon as the temperature drops below the dew point.

Living near water doesn't help as the air will pick up water vapour and will therefore more often be at saturation level - leading to lots of dew, as you have discovered!!

[ChrisLX200]

I stay right by the sea in a glen and whilst the dark skies are superb the dampness and dew is horrendous.

What's the best solution ??

Try to prevent dew forming by having a dew shroud, or using a heater strip/band or both ???

I use a large leisure battery for laptop etc so power isn't a problem.

The two scopes that need something are both Skywatchers - an ED80 and a 200PDS

Any advice most welcome!!!

You need both - dew shield and heater. Dew heaters are adjustable but knowing what setting to use for optimal effect is difficult, on a really bad night I run mine at max which wards off dew from the optics all right but leaves everything else sopping/dripping wet! A bit of a worry when you have an expensive CCD camera or DSLR subjected to those conditions.

ChrisH

[carastro]

I always use a dew heater for my ED80, but the 200PDS will be more problematic.  Is it the 2ndry or the primary that is getting dewed up (yes I have seen the latter happen).  I think you can get dew heaters for the 2ndry, and I "think" you can put a dew heater behind the primary, but never done it.

Carole 

[Uplooker]

I would certainly reaffirm the comments above and say use both a dew shroud and a heater strip/band. If you do not want to spend the money and like a bit of DIY you could use Ni-Chrome wire and build your own drew strap, there are plenty of builds on here just do a search, The Ni-Chrome wire is available from Maplins:-

http://www.maplin.co.uk/p/28swg-resistance-wire-42-ohms-per-meter-bl64u

Use one of these to control it:-

http://www.maplin.co.uk/p/mfa-panel-mounted-speed-regulator-module-rn41u

and stick it in one of these project boxes:-

http://www.maplin.co.uk/p/plastic-box-mb5-gloss-black-150x100x60mm-yn40t

You could also make a dew shield out of a camping mat similar to this:

http://www.millets.co.uk/equipment/103110-multi-mat-camper-mat.html

Its all down to how much you wan to spend or tinker

Hope that helps or just buy something similar to these:

http://www.firstlightoptics.com/dew-prevention/astrozap-dew-heater-tapes.html

http://www.firstlightoptics.com/astronomy-cables-leads-accessories/astrozap-dual-channel-dew-heater-controller.html

Ian

[ChrisLX200]

I've never had the primary dew up on my 12" Newt but I;ve seen the secondary dewed (and covered with hoar frost once). After that I made a 2ft long dewshield out of camping mat and it looked absolutely stupid when fitted - but it worked. Mostly.    I have a plate fitted to the primary end with fans which are only used for initial cooldown, but I figure the reduction in airflow down through the tube also helped a bit. Don't misunderstand - the tube wasn't sealed at the lower end.

ChrisH

[Uplooker]

Hi Chris,

that looks a beast! With that many fans it looks like its ready for take-off!!!! :laugh: :laugh:

Ian

[Skipper Billy]

Thanks all - I figured both solutions might be the answer but thanks for the info and the links.

Chris - that is a BEAUTIFUL tripod!!!

[ChrisLX200]

Ian: LOL, yes you can't observe with them running, that's for sure!

Skip: Thanks, the tripod is home-made and has served will over the years without faliing apart (yet)

ChrisH

[Myopicus]

I've been browsing around t' interweb for a rechargeable hairdryer.  No luck yet, which seems ridiculous when you can buy a rechargeable angle-grinder from any builders merchant.

[sidelight]

I found that using a shield and a heater around the top of the scope stopped dew forming on the secondary as well. I've only had problems with the primary a couple of times, never since I added a shield and that single heater strap. I have the same configuration around my guide scope

Cheers

Ross

Sent from my SM-N9005 using Tapatalk

[Daniel-K]

Astro zap do a heated dew shield from FLO

[tingting44]

im quite surprised dew controller's do not come with self adjusting dew point....my mate made an arduinio dew controller which adjusts the heat of the dew strap to compensate for the change in dew point so you dont ever have to worry about adjusting the temperature......he made the dew controller and dew strap for a couple quid!, for just a standard dew strap and controller your be lucky to get much change from £100 from certain shops!!! so i dont see why they are that much, i would not like to think how much they would be if they were selling self adjusting dew point controllers.....

http://stargazerslounge.com/topic/195752-arduino-dual-dew-strap-controller/#entry2053404

[brantuk]

Rechargeable hair dryers here:

http://www.amazon.com/Cordless-Rechargeable-Hairdryer-FreeDryer-Battery/sim/B003F82PMA/2

[ChrisLX200]

im quite surprised dew controller's do not come with self adjusting dew point....my mate made an arduinio dew controller which adjusts the heat of the dew strap to compensate for the change in dew point so you dont ever have to worry about adjusting the temperature......he made the dew controller and dew strap for a couple quid!, for just a standard dew strap and controller your be lucky to get much change from £100 from certain shops!!! so i dont see why they are that much, i would not like to think how much they would be if they were selling self adjusting dew point controllers.....

http://stargazerslounge.com/topic/195752-arduino-dual-dew-strap-controller/#entry2053404

My SharpSky focus/dew controler has that functionality but I think you need to add a TempHum sensor, then you can set it to monitor temperature changes and it will adjust the power to the dew heaters accordingly. However working 'close to the edge' like that is risky IMHO and a little extra heat will avoid any possibility of dew forming in the first place. Maybe I'm a technophobe...

ChrisH

[JulianFR]

I've been browsing around t' interweb for a rechargeable hairdryer.  No luck yet, which seems ridiculous when you can buy a rechargeable angle-grinder from any builders merchant.

I have also looked long and hard for a rechargeable hairdryer for anti-dew use, but no luck unfortunately. I would have thought there's a gap I. The market there. If you find one I would love to hear about it.

[JulianFR]

Oh... As well as mis-typing I also missed brantuk's post. Will definitely look at that link, thanks.