Dew controller

[m37]

Hey hey!

How do I know how high to have my dew channel set? It works a treat at about 75% even on a heavy dew night but I believe if it's too high it can interfere with seeing?

cheers

[brantuk]

It depends how much moisture is in the air on each session - your setting will change each time. I usually start on low - if it mists up a bit I turn it up a notch - and repeat until it's stays consistently clear. You'll find it settles at, or just above, the dew point. Hth

[m37]

Thanks brantuk, that's great.

[faulksy]

same as brantuk keep your setting low and work up till you have no more fog

[LukeSkywatcher]

same as brantuk keep your setting low and work up till you have no more fog

Agreed.

[BGazing]

Sorry to resurrect this thread...would you say that the setting would depend on humidity, air temperature, or both? Given that the dew point is always somewhat lower than the outside temperature, I'd say that the only parameter to take into account when setting the controller is the humidity. So say 50 perc humidity 50perc setting, 75 perc humidity 75 perc setting or something like that? or should one factor in the temperature and how...

[MattJenko]

My view is a little more heavy handed, life is too short in the UK to even allow any dewing, so I tend to have mine set pretty high all the time.

[BGazing]

haha, point taken. we had a stuffy night yesterday and i guess i undershot a bit.

 

[skywatcher58gb]

You will learn what suits you best, but I normally do as Brantuk says, start low and adjust up if necessary. This way you use less power and conserve as much battery life as possible unless you are working from mains.

[baggywrinkle]

On ‎09‎/‎06‎/‎2016 at 07:53, BGazing said:

Sorry to resurrect this thread...would you say that the setting would depend on humidity, air temperature, or both? Given that the dew point is always somewhat lower than the outside temperature, I'd say that the only parameter to take into account when setting the controller is the humidity. So say 50 perc humidity 50perc setting, 75 perc humidity 75 perc setting or something like that? or should one factor in the temperature and how...

Relative humidity is dependant on ambient air pressure and temperature. The actual onset of condensation is just a fraction of a degree difference between the ambient dew point and the temperature of the scope. On clear night a scope will cool quicker and lower than ambient as heat radiates from the scope. The thin metal work of the tube radiates heat away more quickly and in turn adds to the cooling of the optics.

50% Rh does not equate with a 50% setting. Without strapping a foil type thermometer to the scope the advice above of gentle increments to clear fogging is as good as you will get.

[baggywrinkle]

Unashamed plug! If you go to this website there are a couple of versions of moisture/humidity/dew point calculators.

http://www.michell.com/uk/support/sware-downloads.php

[Waldemar]

Automatic dew control like the digifire units from Kendrick work with two temperature sensors. One to measure the outside temperature and one to measure the temperature in the vincinity of your optics. The integrated software relates the two and insures the heaters will keep your optics free of dew.

The dew point is the temperature on which the air cannot contain the moist anymore and it percipitates (cold air can contain less moist then warm air). Of course there is more to it then this simplified explanation, but basically staying a little bit above ambient will prevent dew to settle on your optics.

Waldemar