Dew Control help please.

[Skipper Billy]

I am being plagued with dew forming and my question is which is the better option - a heated dew shield or the heated tapes ??? (I have tried a plain unheated dew shield which helped but not enough).

I would imagine that the dew shield gives heat over a larger area than the tapes but I would welcome some guidance before purchasing.

It is for use on an ED80. I stay by the side of a Loch which is a naturally damp and cold (but dark!!) area.

Thanks in advance.

[lardy]

Hi,

I use heated tapes with a controller .... no dew problems.

[Daniel-K]

the dew bands work a treat but you will need a controller aswell. I don't know how Ive survived without mine

[Earl]

A controlled band and try an extended shield if you still have problems

[Skipper Billy]

Thanks folks - sounds like a unanimous vote for bands !!

[OneEyedSam]

you can make a dew controller using cheap (£2) motor controllers off ebay. 

[LukeSkywatcher]

A controlled band and try an extended shield if you still have problems

I agree. Use both. No such thing as overkill when dealing with dew.

[ChrisLX200]

You definitely need a shield but not a heated one - all that does is keep the shield itself dew-free. You need heat to go into the optics, the minimum amount and in a precisely controled way, and that is best achieved with tapes+PWM controler. By all means wrap some insulating material over the top of both band and front end of the tube so the heat is directed inwards and it tends to stay there otherwise the heat escapes as fast as you put it in and it becomes a difficult balancing act to get the temperature just right.

ChrisH

[Skipper Billy]

Thanks all - I have ordered a 4 way controller and a dew band and it looks like I can still use my camping mat dew shield as well.

[deepspacehunter]

Hey Skipper Billy ... I use a heated dewcap on my C11 , but on my 6" Refractor  ... a rolled piece of cardboard that extends about 16" past the objective works magically to combat dew, cardboard attracts water, last week we took the Big Refractor out to Deep Sky Country , it was very damp out, the scope was dripping water on us as we observed, but the 6" primary never even fogged up, we observed from midnight until the sun came up, Dew did not shut us down !

Mark

[Tinker1947]

I use one of these on a dew band for my ST-80 guide scope, it runs warm at 8 volt this is reduced from 13.8v....

http://www.ebay.co.uk/itm/New-LED-Dimmer-Manual-Knob-Switch-Light-Monochrome-12-24V-Low-Voltage-Controller-/201106991271?pt=UK_Home_Garden_Lighting_Parts&var=&hash=item2ed2e928a7

[astronymonkey]

Hi Billy,

I think there have been lots of good replies which I completely agree with. With dew the key is to preventing it from happening and then having a strategy in place to deal with it if it takes hold.

Good housekeeping:

For me I make sure that whenever the scope is outside cooling then the only cover I remove tends to be the focusser one in order to vent the tube.

Once Im observing , with all the caps off etc I make sure that between objects I tilt the tube so it is horizontal so any settling dew from the air above doesnt land on the optics, this means that while Im looking at star maps etc and deciding what to do next I dont have excessive dew dbuilding up. In addition to this I keep the lid on my eyepiece case closed apart from when i change Eyepieces.

Active dew control:

The dew tapes do work really well, and with a controller its possible to balance the heat that is needed which can also preserve battery life. In addition to these I also have a secondary heater fitted directly behind the mirror (for me this is the most impoartant one on a newtonian as dew on this little mirror is difficult to manage - ie I would think twice about wiping it with a lens cloth due to possible damage to the surface and knocking colimation out .... it can also be a devil to get to. The key here is to turn the system on before dew hits in order to keep the optics above the dew point - I tend to go for 15-30mins on full as an initial warm up and then drop down to about 25-30% on the controller depending on conditions. On a frac a dew sheild made from a camping mat as you suggest is also a good addition, as is a light shroud for those with an open tube dob.

What if dew hits:

In reserve i also have a 12v hair dryer which I only use in emergencies. This drains power and can over-heat optics if used for too long but in some cases if the dew bands havent been on a high enough setting and dew has began to form then a quick blast from the hair dryer tends to warm the optics enough until the heater bands can catch up. At kielder last year I left my scope while it was cloudy with no dew heaters switched on and when it cleared a layer of frost was on my secondary and all over the tube, after 1-2 mins with the hairdryer melting the dew and then evporating it, I put the secondary heater on and managed to recover what would have otherwise been a lost session - from now on , if dew is possible and its cloudy I often leave the dew heaters on low whilst I wait for the clouds.

In general, with good heaters and a bit of a plan, dew shouldnt be a problem. Id say dew prevention is one of the best mods you can make to a scope.

Clear skies