Dew-stroyed session

[bosun21]

Last night was the proverbial nightmare session to be forgotten. I set up my achro this time out (Evostar 120/1000) on an AZ4 with steel tripod as it had been relegated due to the acquisition of my 102ED Starfield. I could feel the dampness in the air but had no idea what was in store for me. As I was sitting on my chair letting the last vestiges of light disappear, I was surprised to see that the metal armrests on my chair was wet with dew. I reached up to my telescope tube and it was soaking wet. My eyepiece was wet also. I changed eyepieces and tried to set my focus on Altair, but it was just like looking through a goldfish bowl. I then saw that the dew shield on my Evostar had lost its battle against the dew monster. This gentlemen/women was my first proper introduction to bad dew. I packed up without observing anything and had to leave everything open and uncapped to the warm indoors to dry out. I guess it’s time to purchase some anti dew equipment. for my scopes. Is it dew bands or dew shields? 12v or 5v. I am hoping for some advice from folk who have battled and slain the dew monster. Thanks 

[OK Apricot]

Ideally dew straps with a controller and 12v source. I've recovered a night having had the old Mak dew up - put the strap on and twenty mins later it was good to go 🙂. I think the result speaks for itself really - the large shield on the 120 wasn't enough for those particular conditions so you need a new weapon. 

[Guest]

Being in the American Mid West (Ohio) I am all to familiar with dew, and not that little light stuff either.  I am talking the serious coats everything and you watch it run down your scope kinda dew and the rain gauge thinks you picked up a half inch.  I dont mess around, i have a full on 4 band controller for my 10 inch dob.  One around the front of the OTA, one on the finder and one for the eyepiece.  The finder i tend to run around 50 percent all the time and it keeps both ends clear.  The one around the OTA rarely goes above 50 percent, usually around 25 percent keeps the secondary clear.  The eyepieces are the tricky one.  1.25 inch take less then the 2 inch.  Add a Barlow to the mix and there is another piece of glass to keep clear.  You will have to play with your settings a bit.  Watch your equipment while setting up.  If it is getting wet, get the heaters on at 50 percent and back them down.  Good luck

[bosun21]

2 minutes ago, Mike Q said:

Being in the American Mid West (Ohio) I am all to familiar with dew, and not that little light stuff either.  I am talking the serious coats everything and you watch it run down your scope kinda dew and the rain gauge thinks you picked up a half inch.  I dont mess around, i have a full on 4 band controller for my 10 inch dob.  One around the front of the OTA, one on the finder and one for the eyepiece.  The finder i tend to run around 50 percent all the time and it keeps both ends clear.  The one around the OTA rarely goes above 50 percent, usually around 25 percent keeps the secondary clear.  The eyepieces are the tricky one.  1.25 inch take less then the 2 inch.  Add a Barlow to the mix and there is another piece of glass to keep clear.  You will have to play with your settings a bit.  Watch your equipment while setting up.  If it is getting wet, get the heaters on at 50 percent and back them down.  Good luck

Yes I will probably be doing much the same thing as yourself. I will start off at the 50% as you recommended and tailor it from there. All I know is that next time I’ll be better prepared for it. It just totally KO’d me last night and was indeed a lesson learned.

[Mick H]

A hairdryer works for me.

[Carl Au]

Interesting. I was out in lovely bortle 4 skies in the Lincolnshire Wolds last night, no dew whatsoever up there. I have been using refractors for years and years, since I was 11 I think (I am 59) and I don’t think I ever had a session I had to end early to due. 
 

I was wondering about the temperature of your scope before you took it outside and the temperature outside when you started observing, could be a factor.

[bosun21]

25 minutes ago, Carl Au said:

Interesting. I was out in lovely bortle 4 skies in the Lincolnshire Wolds last night, no dew whatsoever up there. I have been using refractors for years and years, since I was 11 I think (I am 59) and I don’t think I ever had a session I had to end early to due. 
 

I was wondering about the temperature of your scope before you took it outside and the temperature outside when you started observing, could be a factor.

I took it outside about an hour before sunset to let it reach equilibrium temperature. It was a very strange night as I swear I could actually feel the moisture in the air on my face. I have experienced dew many times before and like you said, it could be dealt with without too much fuss. However this was just a freak night in my opinion.

[Carl Au]

Interesting 

[Guest]

Have you gone back and looked at what the environmentals were that night.  Maybe write them down and avoid nights like that lol.  I have gotten pretty good and walking outside and going .... Nope not tonight. 

[bosun21]

1 hour ago, Mike Q said:

Have you gone back and looked at what the environmentals were that night.  Maybe write them down and avoid nights like that lol.  I have gotten pretty good and walking outside and going .... Nope not tonight. 

Just checked it and the humidity was 95%

[Guest]

2 hours ago, bosun21 said:

Just checked it and the humidity was 95%

Which is what we have normally in August.  May I assume 95% is outside of the norm for you? 

[bosun21]

4 hours ago, Mike Q said:

Which is what we have normally in August.  May I assume 95% is outside of the norm for you? 

It is pretty rare but not unknown. I reckon that there’s been more than one factor at work that night to create a perfect storm (sic) of dew formation.

[Guest]

That was this morning at 5 am.  It is still 79 percent humidity at almost 5pm