Dew Heaters

[Littleguy80]

On a recent dark site trip, I had real issues with dew on my eyepieces. I'm thinking I may need to invest in a dew heater. My Telrad and 9x50 Finder can suffer with dew too. Primary mirror (10" solid tube dob) doesn't seem affected. I don't think the secondary dewed up either. Any recommendations for dew heaters or other solutions to beat the dew?

Many thanks

[domstar]

You wouldn't be the first to call me a cheapskate but a toilet roll tube fixed with an elastic band on my 9x50 finder has worked wonders. There's always a lid over my eyepieces when they're not in the scope and I've never had a problem with them but, as you know, my sessions are shorter than yours. 

[Littleguy80]

1 minute ago, domstar said:

You wouldn't be the first to call me a cheapskate but a toilet roll tube fixed with an elastic band on my 9x50 finder has worked wonders. There's always a lid over my eyepieces when their not in the scope and I've never had a problem with them but, as you know, my sessions are shorter than yours. 

lol whatever works! My Telrad dew shield is a cheap homemade "work of art". I put the eyepieces back in the case but am guilty of not putting the end caps back on when they're not in use. Perhaps doing that will be enough

[GavStar]

These work well for me

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

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

https://www.firstlightoptics.com/batteries-powerpacks/tracer-12v-8ah-lithium-polymer-battery-pack.html

[domstar]

My impression is that dew falls vertically on stuff - I never get any when I'm on the balcony. I hope someone can confirm or correct this. If it's true, then eyepieces can just be covered. Probably not so simple, though. By the way, with my Lidl scope I often left the caps off and I absent-mindedly used to check if I had by touching the lens with my thumb. Against most advice, I still think it's best to start off with cheap gear for reasons such as this. 

[BGazing]

13 minutes ago, domstar said:

My impression is that dew falls vertically on stuff - I never get any when I'm on the balcony. I hope someone can confirm or correct this. If it's true, then eyepieces can just be covered. Probably not so simple, though. By the way, with my Lidl scope I often left the caps off and I absent-mindedly used to check if I had by touching the lens with my thumb. Against most advice, I still think it's best to start off with cheap gear for reasons such as this. 

It does not fall...take a cold bottle from the fridge and observe that it forms on all surfaces immediately.

Top of the balcony shields you from losing heat to sky above, that is why it is not dewing.

[Littleguy80]

Just found this fancier version of @domstar's 9x50 homemade finder dew shield by @nightfisher

 

[domstar]

21 minutes ago, BGazing said:

It does not fall...take a cold bottle from the fridge and observe that it forms on all surfaces immediately.

Thanks. What about a bottle (or telescope) that is the same temperature as outside? Water doesn't condense on it at all unless there is dew. I'm surprised that my balcony can never be cold enough for dew to form. When I bring it inside from the balcony, the scope is much colder and you should see the condensation. (Excuse my stupidity).

[BGazing]

That is because inside the air is warmer, more saturated with vapour and dewing point is higher. Kinda like the fridge example.

The moral is to cap the telescope outside, put it in a bag, bring the bag inside and the temerature will slowly equalize without having the scope dew all over.

Your balcony has to be colder than ambient in order for dew to form because, to simplify, dew point is (almost) always lower than ambient. Shielded balcony cannot radiate away enough heat to dew over. Cars in the street do all the time...as you can see in the morning.

[domstar]

@BGazing. Thanks. I think I get condensation. How does it work when there's no temperature differential, like when a telescope is the same temperature as outside? As the air cools it's unable to hold as much moisture? Is this wrong? I always thought the objective dews over when I'm pointed up near the zenith. Everyday is a school day. 

Sorry Neil. I seem to have trampled all over your thread.

[BGazing]

Objective or corrector plate looking at the zenith cools quicker than when pointed down when the dew shield protects it. That is when the dew heaters help.

If your telescope is at ambient temperature, you are good. But the trick is it usually is not and cools quicker...

[domstar]

Sorry to be a pain @BGazing but how can a scope left outside get colder than the ambient temperature if the ambient temperature is falling (rather than warming up in the morning)? 

[BGazing]

http://www.dewbuster.com/faq-1a-questions.html#FAQ

[domstar]

@BGazing Thanks for your time and patience. I didn't know any of this. I'm astonished. Thanks again.

[Littleguy80]

Well my dew prevention system is now in place! Tracer battery powering a 4 channel dew controller. Astrozap 2” eyepiece dew heater and Revelation pro Telrad dew heater. 

I made my own finder dew shield using @nightfisher‘s guide. The one shown is mark 2, which I’m still not 100% happy with but it’s much better than my first try. DIY is not one of my strengths. I’ve used some blackout material inside that my wife had going spare. 

As always, thanks to all the good folks who helped and advised! 

[Stu]

Looking good! Hope it does the trick, it should do  

[N3ptune]

3 hours ago, Littleguy80 said:

Well my dew prevention system is now in place! Tracer battery powering a 4 channel dew controller. Astrozap 2” eyepiece dew heater and Revelation pro Telrad dew heater. 

I made my own finder dew shield using @nightfisher‘s guide. The one shown is mark 2, which I’m still not 100% happy with but it’s much better than my first try. DIY is not one of my strengths. I’ve used some blackout material inside that my wife had going spare. 

As always, thanks to all the good folks who helped and advised! 

That's a beautiful setup, a large 10" solid tube with this beautiful Dobson mount and dual speed focuser. Very nice!

[Sunshine]

On 10/05/2018 at 08:39, Littleguy80 said:

On a recent dark site trip, I had real issues with dew on my eyepieces. I'm thinking I may need to invest in a dew heater. My Telrad and 9x50 Finder can suffer with dew too. Primary mirror (10" solid tube dob) doesn't seem affected. I don't think the secondary dewed up either. Any recommendations for dew heaters or other solutions to beat the dew?

This is a great article on dew, its causes, and best control methods.

http://www.skyandtelescope.com/astronomy-resources/dealing-with-dew/

[cjdawson]

Here's a cheap solution, as you keep your eyepieces in a box...

Put a hand warmer in with them.  That'll last for 10 hours and stop the dew on your eyepieces.  (except the one on the scope)

https://www.amazon.co.uk/Hands-Instant-Hand-Warmers-Pairs/dp/B000YF3DUA/ref=sr_1_1?ie=UTF8&qid=1528462975&sr=8-1&keywords=handwarmer

If you want reuseability, try something like this...

https://www.amazon.co.uk/【shipping-uk】Rechargeable-Reusable-Electric-Portable/dp/B0756DZ78P/ref=sr_1_3?s=sports&ie=UTF8&qid=1528463060&sr=1-3&keywords=hand+warmer+electric

 

[N3ptune]

I found that the light of a  flashlight, especially my old Maglite with a light bulb will emit a surprising amount of heat. I put that light close to the front lens of the eyepiece to dissipate dew. It's working fairly fast has a temporary reheating solution to correct a breathing accident or an eye too close to the front lens of the eyepiece.

That is the exact flashlight with the xenon lights, old technology but still very good.

https://www.amazon.co.uk/Maglite-M2A016-Mini-Torch-Blister/dp/B00002N6SL/ref=sr_1_12?s=sports&ie=UTF8&qid=1528497525&sr=1-12&keywords=maglite+bulb