Dew shields do they work

[paler31]

hi i was using my telescope last night to take some images of andromeda. I had set my computer to take 5min exposures at iso 800. looking back at the pictures they gradually got dimmer and dimmer. I noticed that the front of the scope was covered in dew and put the poor image quality down to this. My question is do dew sheilds actually work? will they just slow the formation of dew? what is the best one to get and from where? should i be using somekind of heated dew sheild? any help would be appreciated, i should have said that i have a celestron c6 sgt scope and mount.

John

[VigdisVZ]

Yeah, you can make a DIY shield with a camping mat and gaffa tape. It will delay the formation a while depending on weather. If you still have problems the telescope shops sell battery powered heating bands.

[CJBooth]

Hi John,

You can get a nice dew shield with a heated band. It's quite good value as the dew strips and separate shield can cost quite a bit.

http://www.firstlightoptics.com/dew-prevention/astrozap-flexi-heat-dew-shields.html

This would be the best protection against dew IMO.

Craig

[Alan_B]

A C6 will certainly need a dew shield (especially in UK) and they do work to a certain extent but will not completely solve the dew problem.

Dew heater tapes are the way to go to have any chance of a dew free session when the conditions make scopes susceptible

[paler31]

thanks for the info guys i will look into heated strips.

john

[Moonshane]

the problem with imaging is that the scope is pointed in the same direction for a long time. if visually observing you tend to move the scope about more and therefore the heat loss on the optics directly to space is lower. I agree with other posts that a dew shield/heater band should work for your scope. for visual a camping mate type home made dew shield would be fine.

[Charon]

Dew is terrible out here this time of the year and I was forever having problems. So I bought a Astrozap Flexi-heat Dew Shield from FLO, end of dewing problems.

[VigdisVZ]

I'm borrowing the thread: What happens with dew when its under freezing temp?

[fredster]

My Mak will last just a few minutes when dew is bad, even with the dew shield on. Without a shield the scope will start dewing over immediately, with the shield it may hang on 5-10mins. In other words just at the moment you get yourself settled at the eyepiece its over. Dew heaters are the only answer. But remember they are a proactive solution, not reactive. If the corrector has dewed over it will take an age for the dew heater to recover things. In that instance its time for a hair dryer.

I have a four port dew controller, dew strap on the corrector plate, dew strap on the finder and a dew strap on the eyepiece. I set the whole lot going on low power 1 hour before going out. No dew for the whole session.

[brantuk]

@Vig - Under freezing temperatures - dew does the same as it does on your car roof in the winter mornings - it freezes! However you can't get dew straps big enough for a car - but I'd recommend them for the scope lol.

[VigdisVZ]

@Vig - Under freezing temperatures - dew does the same as it does on your car roof in the winter mornings - it freezes! However you can't get dew straps big enough for a car - but I'd recommend them for the scope lol.

Your logic is flawless, I should have seen that myself

[Orionis]

I use dew shields on all my telescopes with good success.

Some are purpose built ABS plastic others are homemade using camping mat foam.

Although passive dew prevention is good a dew heater is more effective at keeping the dew at bay.

The corrector plate of a C6 is a lot of glass to passively prevent dew.

[Brighton Belle]

sorry if this is a daft question but how do heated dew shields work if you are in the middle of nowhere? Do they plug into your car cigarette lighter, or is that too simple? Perhaps I could get a solar powered one......

[VigdisVZ]

sorry if this is a daft question but how do heated dew shields work if you are in the middle of nowhere? Do they plug into your car cigarette lighter, or is that too simple? Perhaps I could get a solar powered one......

Since you're already carrying a battery tank or car battery for your GO-TO mount, camera, laptop, guide setup you can easily heat a few low power heaters.

[michael.h.f.wilkinson]

I plug mine into a battery pack (via a controller). It actually draws quite a bit more than the little stepper motor of my mount. I find I can get away with just the shield most nights, but need a heated dew strip on really humid nights.

[Brighton Belle]

Since you're already carrying a battery tank or car battery for your GO-TO mount, camera, laptop, guide setup you can easily heat a few low power heaters.

I haven't got a GO-TO, or a camera and I don't plan to take my laptop to remote sites, I'm a beginner and my equipment is basic!

[M4lcs67]

I will be going down the route of a heater tape and conrollerwhen I get my scope out in a few weeks. I gave it it's first outing back in July with a dewsheild attached, but it didn't do anything so that is why I am having to get the tape. I already knew that large SCT's were suceptable to fogging up, but this problem I had just confirmed it.

[cotterless45]

For the diy option;http://www.dewityourself.com/6-dew-heater-kits

[kirkster501]

Seems mad doesn't it... We have to wait for scopes to cool down to ambient to get best performance. And then we warm the front to keep dew off!

[mert]

Does anyone observe near a river or loch? Is it worse at these places?

[paler31]

some great advice here one thing is worrying me though and that is how much power they draw. I have a celestron power tank so should have no problem connecting a dew strap controller but how long can i expect to run it for before needing a recharge.

[brantuk]

I got a dob out next to a fishing lake once - big mistake - had to pack up 20-30 mins later - barely got a look in. Lesson learned lol.

[VigdisVZ]

Does anyone observe near a river or loch? Is it worse at these places?

I'm interested in this. Also does lowland fields (like ancient seabottoms) dew differently from say hills and mountains? Because sine most of Uppland is old lake bottom it feels like the dampest place in the world at times.

[SniffTheGlove]

some great advice here one thing is worrying me though and that is how much power they draw. I have a celestron power tank so should have no problem connecting a dew strap controller but how long can i expect to run it for before needing a recharge.

You can work it out with a multimeter (if you have one)

1) Measure the Ohms of the heater strip.

2) Calculate voltage*voltage

3) Divide by Ohms to get the wattage

4) Divide wattage by voltage to get current rating.

eg.

34 Ohms Resistance measured

12vdc * 12vdc = 144vdc

144vdc / 34Ohms = 4.23watts

4.23watts / 12vdc = 0.35Amps

[VigdisVZ]

Thanks for the calculation. I am no scholar, but I'm beginning to realise that it's not hard to build these things yourself with basic electricity knowledge. Already looking at DIY parts.

Speaking of dew and frost. I actually noticed something this morning (since Stockholm got its first hit of morning frost today). My car windows were all frosted over. Except a small patch underneath an aerodynamic part I have above my back window. This indicates that frost really do seem to fall from above, which in turn seems prove the concept of a dew shield.