Dew Control

[Stardaze]

I suffered dew badly on Friday night, after 2 hours observing. I wasn't expecting the problem until later in the year, and so would like to hear everyones thoughts on the subject.

I have a 10" dob, and suffered the Telrad, 9x50 finder and EP's all being affected. What are your own solutions? I had thought some dew bands later in the year, but interested to know recommendations on the kit needed. 

 

 

[Tenor Viol]

The air the other day in the UK was highly saturated. The moment the air temp drops below the dew point then it's inevitable. Forecast for tonight is dew point is around 10C and minimum temperature is 11C...

I'm still waiting for my 'scope to arrive, but I'm intending to buy dew bands straightaway

[Stardaze]

6 minutes ago, Tenor Viol said:

The air the other day in the UK was highly saturated. The moment the air temp drops below the dew point then it's inevitable. Forecast for tonight is dew point is around 10C and minimum temperature is 11C...

I'm still waiting for my 'scope to arrive, but I'm intending to buy dew bands straightaway

Bands as far as I'm aware can cover your EP's and finders but I'd like to know more about the ones that wrap around the OTA - do they really work? There seems to be a myriad of suppliers with plates that attach to the rear of the secondary too. And how does the Astrozap heated dew shield actually work when the heat would be around the top ie. nowhere near the mirrors?

In hindsight, last Friday night was very saturated and I hadn't expected it at this time of year. But even my primary had a little bit of dew on it when I put the OTA away for the night. Maybe flocking and/or a fan could help? What's the best way/product to power all of this too?

[wookie1965]

Yes they do I use them on my refractors if you are using a newt make a dew shield out of a camping mat works wonders you can always get some thin plastic and glue that to the mat.

Edited June 22, 2020 by wookie1965

[John]

I keep my eyepieces at a warmer than outside temperature to stop them misting or dewing.

Other than that, I've not found dewing an issue with my 12 inch dob

Where we live and I observe from is 300 ft above sea level so maybe that makes a difference ?

[Stardaze]

8 minutes ago, John said:

I keep my eyepieces at a warmer than outside temperature to stop them misting or dewing.

Other than that, I've not found dewing an issue with my 12 inch dob

Where we live and I observe from is 300 ft above sea level so maybe that makes a difference ?

My town is 410' above John? It took 2 hours Friday for it the have a detrimental effect and nearer 3, for it to be noticeable on the optics inside. In the winter months, I very much doubt I'd be out for that length of time, but I'd like to get my head around it. I live on the edge of town in a relatively high spot. Simple bands around my finders and a shield might be enough? 

Edited June 22, 2020 by Stardaze

[Pixies]

I'm at sea-level (about 100m from the beach). No issues yet, this year, but have been thinking about getting prepared for the dew.

I'm unclear about using dew bands/heaters with a dob. I thought we were busy trying to get everything at a stable equilibrium temperature-wise, rather than having anything that might create convection currents? I understand how a dew shield would keep the moisture away from the mirrors, and how we can use heating devices on EPs and finders. But surely we don't want to start heating up parts of the OTA?

[Stardaze]

47 minutes ago, Pixies said:

I'm at sea-level (about 100m from the beach). No issues yet, this year, but have been thinking about getting prepared for the dew.

I'm unclear about using dew bands/heaters with a dob. I thought we were busy trying to get everything at a stable equilibrium temperature-wise, rather than having anything that might create convection currents? I understand how a dew shield would keep the moisture away from the mirrors, and how we can use heating devices on EPs and finders. But surely we don't want to start heating up parts of the OTA?

My thoughts exactly..

Edited June 22, 2020 by Stardaze

[Jiggy 67]

2 hours ago, Pixies said:

I'm at sea-level (about 100m from the beach). No issues yet, this year, but have been thinking about getting prepared for the dew.

I'm unclear about using dew bands/heaters with a dob. I thought we were busy trying to get everything at a stable equilibrium temperature-wise, rather than having anything that might create convection currents? I understand how a dew shield would keep the moisture away from the mirrors, and how we can use heating devices on EPs and finders. But surely we don't want to start heating up parts of the OTA?

Dew bands should be used in conjunction with a controller that can regulate the heat. I use them on my OTA and they can prevent dew by just raising the temperature above the dew point without creating any major currents. I have an ep one as well but find that to be pretty useless, a warm pocket is the fix for those I think 

[Stardaze]

42 minutes ago, Jiggy 67 said:

Dew bands should be used in conjunction with a controller that can regulate the heat. I use them on my OTA and they can prevent dew by just raising the temperature above the dew point without creating any major currents. I have an ep one as well but find that to be pretty useless, a warm pocket is the fix for those I think 

Silly question... where do you wrap the band around the OTA? Top, middle, bottom..

[Jiggy 67]

I wrap mine around the bottom, adjacent to the mirror (a newt)

[Stardaze]

2 hours ago, Jiggy 67 said:

I wrap mine around the bottom, adjacent to the mirror (a newt)

What regulator and power supply do you use? Do you use a shield around the top too?

[wookie1965]

https://www.ebay.co.uk/itm/Dimmer-12v-DC-DC-8A-Regulator-Intensity-Led/252447321034?hash=item3ac7086bca:g:QY4AAMXQrhdTREnF

One of these with a 12v supply

[Jiggy 67]

...........or one of these

https://www.firstlightoptics.com/dew-prevention/hitecastro-four-channel-four-port-dew-controller.html

No I don’t use a dew shield but I do keep considering it. Many say a newt doesn’t need one as they are kind of a natural dew shield themselves but I think I would benefit from one for the secondary maybe 

[Stardaze]

How far do you go with it? You could have the heated shield with a band around the bottom and bands around telrad and finder, with a 4 way controller and power supply for £250+ 🤔

[John]

1 hour ago, Stardaze said:

How far do you go with it? You could have the heated shield with a band around the bottom and bands around telrad and finder, with a 4 way controller and power supply for £250+ 🤔

And bands to fit around around the eyepiece and heated wires installed behind the secondary mirror ........

I'm very glad that it's not an issue here.

 

[Stardaze]

7 minutes ago, John said:

And bands to fit around the eyepiece and heated wires installed behind the secondary mirror ........

I'm very glad that it's not an issue here.

 

Found a cheaper solution here https://www.amazon.co.uk/Bartscher-Electric-patio-heater-2000D/dp/B002XC3FEG/ref=asc_df_B002XC3FEG/?tag=googshopuk-21&linkCode=df0&hvadid=435913082336&hvpos=&hvnetw=g&hvrand=2067592359596679348&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1007011&hvtargid=pla-826161128049&psc=1&tag=&ref=&adgrpid=98056361181&hvpone=&hvptwo=&hvadid=435913082336&hvpos=&hvnetw=g&hvrand=2067592359596679348&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1007011&hvtargid=pla-826161128049

😆

[Pixies]

I'd pay one of the kids to stand there with a hairdryer!

[iwols]

i tend to use one all of the time albeit when its like this i tend to have it set to 25 percentish,suspect when it is too high it tends to effect the image very slightly

[Stardaze]

19 minutes ago, iwols said:

i tend to use one all of the time albeit when its like this i tend to have it set to 25 percentish,suspect when it is too high it tends to effect the image very slightly

As in,  large single band around the OTA? At the bottom?

I'm wondering whether a shield and strap as the bottom would suffice. 

Edited June 24, 2020 by Stardaze

[Stardaze]

I've ordered a system through Dew Control in the end. Tim is extremely helpful and has added an additional extra lead for adding a remote battery pack later on, so great service. The RACI strap won't be in for a week or two but I've gone for their specific Telrad heater, a large strap for the OTA, a 4 way controller and mains pack. Thanks to @Littleguy80 for recommending Dew Control. Might not bother with an EP strap as most seem to say they're not so effective. 

[baggywrinkle]

The difference between dew and no dew is fractions of a degree.

Glass as well as the OTA tubing will radiate away heat and actually cool below the dew point predicted by a calculation based on ambient temperature, local ambient pressure and the local relative humidity.

Dew heaters and dew shields will help prevent dew formation.  One by forming a columns of stable air over the objective or corrector plate, the other by additional heating raising the temperature to above  the phase change between gaseous water vapour and the liquid phase. Water can be tri phase, gaseous, liquid and ice.

Eyepieces in pockets will delay the onset of dew formation but not prevent it. Left long enough in the telescope they will cool too.

[Stardaze]

7 minutes ago, baggywrinkle said:

The difference between dew and no dew is fractions of a degree.

Glass as well as the OTA tubing will radiate away heat and actually cool below the dew point predicted by a calculation based on ambient temperature, local ambient pressure and the local relative humidity.

Dew heaters and dew shields will help prevent dew formation.  One by forming a columns of stable air over the objective or corrector plate, the other by additional heating raising the temperature to above  the phase change between gaseous water vapour and the liquid phase. Water can be tri phase, gaseous, liquid and ice.

Eyepieces in pockets will delay the onset of dew formation but not prevent it. Left long enough in the telescope they will cool too.

I'm taking the 'belt and braces' approach and will order a strap for EP's too. It's the kind of thing that will really annoy me when, the law of sod dictates that that the most perfect of evenings is spoilt, so I'll get myself as equipped as can be. 

[davhei]

I also have a 10” dob and regularly observe close to the sea with high humidity. Never had the primary fog over but occasionally I’ve had to abort a session because of dew on the secondary, finder scope and sometimes eyepiece.

What I did was cut up a camping mat and duct tape it together to make a dew shield. Around 50-55 cm long if I recall. Never had problems with the secondary fogging up since.

For the finder scope I’ve made a habit of keeping the dust caps on whenever I am not using it. Has done the trick for me so far.

EPs are less of an issue, but if I am not observing and it is humid I use a dust cap if it is in the scope. I usually put the EPs in a padded case with the caps on when not in the scope. Seems to keep them from fogging over most of the time.

(tea towel was to avoid the sun shining into the OTA when I was waiting for the occultation of venus a while back)

 

Edited August 21, 2020 by davhei

[Stardaze]

7 hours ago, davhei said:

I also have a 10” dob and regularly observe close to the sea with high humidity. Never had the primary fog over but occasionally I’ve had to abort a session because of dew on the secondary, finder scope and sometimes eyepiece.

What I did was cut up a camping mat and duct tape it together to make a dew shield. Around 50-55 cm long if I recall. Never had problems with the secondary fogging up since.

For the finder scope I’ve made a habit of keeping the dust caps on whenever I am not using it. Has done the trick for me so far.

EPs are less of an issue, but if I am not observing and it is humid I use a dust cap if it is in the scope. I usually put the EPs in a padded case with the caps on when not in the scope. Seems to keep them from fogging over most of the time.

(tea towel was to avoid the sun shining into the OTA when I was waiting for the occultation of venus a while back)

 

Thanks for the info. it's going to be a little trial and error I guess. I am going to add a shield too I think to my next order. Have wondered whether a DIY shield for the RACI might negate a heated band being needed there?

Edited August 21, 2020 by Stardaze