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dew heater ? etc

glyn lacey

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glyn lacey

glyn lacey

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Posted

Hi all , OK I've picked up the cool down tip ,but my next question is what's the story about dew,,very basic questions I know , please forgive me,I prefers to hear it from people on the ground (so to speak) than decipher it from a book.

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maxheadroom

maxheadroom

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Dew from moisture in the air will condense on cold surfaces at certain temperatures (dew point). You don't want this to happen on the glass bits for obvious reasons! (Take a beer out of thee fridge and water condenses on the can in a warm room)

Dew heater strips placed in specific areas like round the primary mirror, eyepiece, finder-scope will ensure that the temp in these areas does not drop lower than the dew point and thus they will remain clear for your viewing pleasure.

You will need a controller and heater bands. I have a 4 port controller. One round my primary, one round my eyepiece and one round my laser (dew doesn't effect lasers but they don't work in cold so it solves this problem too)

I hope this helps!

Max

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maxheadroom

maxheadroom

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You will need a controller and heater bands.

It depends on if the scope is a SCT,refractor, reflector etc.

We dont know what scope Glyn has.

Fair point I only know about SCTs because that's what I own. I should have mentioned the dew shield too. Mine was a water magnet before I sorted it out :(

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LukeSkywatcher

LukeSkywatcher

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Fair point I only know about SCTs because that's what I own. I should have mentioned the dew shield too. Mine was a water magnet before I sorted it out :(

I only point out what may be needed because i own an SCT, two refractors and a reflector and when it comes to dew prevention, all 4 scopes i own need different methods of dew prevention.

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todd8137

todd8137

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The first question is what kind of scope do you own?. Some scopes will need/benefit from a heated dew strap, while others may just need a dew shield (two different things).

Also some scopes (refractors) do not really need a cool down period, while relectors do.

My 5" edt defo needs a dew band !

Pat

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Andy Milner

Andy Milner

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Just out of interest what would be recommended for my 200p explorer reflector? I'm just starting out.  I read another thread where someone suggested cutting some sports foam mat and wrapping to create a dew shield. Any experiences with this scope with dew heaters? I guess id need to do the primary mirror, eye piece and finderscope too...

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PorkyB

PorkyB

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Just out of interest what would be recommended for my 200p explorer reflector? I'm just starting out.  I read another thread where someone suggested cutting some sports foam mat and wrapping to create a dew shield. Any experiences with this scope with dew heaters? I guess id need to do the primary mirror, eye piece and finderscope too...

For my 200p I use a camping mat dew shield to protect the secondary mirror and a couple of heater bands for the eyepiece and finder.  It's very rare for dew to affect the primary mirror.

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jason.p

jason.p

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Just out of interest what would be recommended for my 200p explorer reflector? I'm just starting out.  I read another thread where someone suggested cutting some sports foam mat and wrapping to create a dew shield. Any experiences with this scope with dew heaters? I guess id need to do the primary mirror, eye piece and finderscope too...

my 200p has a thin foam dew shield and dew straps on the finder, secondary and primary. I'm not sure if these strsps are really necessary, but the one I fixed on the Telrad works a treat.

post-23638-0-83103900-1392191747_thumb.j

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Andy Milner

Andy Milner

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I just used my 200p and eq5 for the first time last night. Completely ruined by a fogged up primary mirror and secondary mirror. Was struggling with polarscope then realised that had dew too. My entry into astronomy is going slow.

I think I will benefit from any tips given here. I've noticed dew heater bands and a controller are not cheap. Not interested in making my own as beyond my expertise. I do like the camping matt idea for a shield.

Anyone know cheapest prices for dew controller kits? It seems I will need to spend over £100 to keep dew at bay.

Hair dryer idea seems like a pain in butt and noise will annoy neighbours.

Cheers, Andy

Sent from my iPhone using Tapatalk

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PorkyB

PorkyB

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If dew conditions are so bad that your primary fogs up then it's probably time to pack the scope away and sit in your chair with a nice cup of tea (beer, whiskey, etc.) and just enjoy looking at the night sky.

Dew conditions vary massively and I've only had two sessions in the last year that were bad enough to stop me.  Normally, with my Newts, it's just the eyepiece and finder that get foggy.  With a Mak or a refractor you will also need to protect the front glass element.

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JulianFR

JulianFR

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Has anyone ever seen a portable battery operated hairdryer that could be used while observing in the middle of nowhere? I've seen a couple of car cigarette lighter-powered fans (very weak) but nothing that could be used away from the car.

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PeterCPC

PeterCPC

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I have a CPC800 and tried a battery powered hairdryer. Plugged into the PowerTank cigar lighter socket. It had 165w output and was just not up to the task and really took a lot out of the battery. I would not bother with battery powered hairdryer if I were you. 

I use a dew controller and a heater strip on the corrector but I still have to have some shots with a mains hair dryer from time to time to keep the mist at bay.

I think that the extreme weather we are getting means that the air is high in humidity as the ground is so wet and the water is evaporating all the time.

Peter

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Carbon Brush

Carbon Brush

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My favourite is the hair dryer. Use it when and where needed. Fits any scope and is cheap.

Having said that, you sometimes don't realise immediately that things are fogging. A well fogged corrector plate can (till you look up) just make you think viewing has worsened a little.

Another good use for the hair dryer is warming up everything at the end of the session. If returning to the house, it is much easier and quicker to bring the scope and accessories above the indoor dew point.

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Gomtuu

Gomtuu

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Probably a silly question, but I have a SW 200PDS and am thinking of getting a dew heater for the secondary mirror and the eyepiece - where/how should the respective heaters be attached?

I already use a dew shield.

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brantuk

brantuk

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You can get small dew bands that just wrap round the eyepiece - they come in 2" and 1.25" varieties.

The secondary depends on it's shape and size and whether it's on a stalk or not. But they all fit on the top side - you can get them shaped to fit specific sizes of secondary - or you can get the generic stick on "pad" types.

It's usually a good idea to put some reflective insulating material on top secondary heaters to keep the heat going down onto the back of the mirror. Hth :)

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brantuk

brantuk

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I was recommended a layer of insulating foam by a retailer - you can get it in pressurised tubes that spray on from B&Q but you have to have a mould for the initial shaping. When I found out how much it was I didn't bother.

I'm going to build up a few layers of duct tape with some insulating foil wedged in between two layers - when I get round to fitting it. The back of my secondary is like Teflon and difficult to stick anything to it lol. Then you need to route the wires via a spider and through the tube (or over the end) and down to a battery. It's a big job for such a small item.

For the primary you can fit a computer case fan behind it to keep the air flowing over the mirror surface reducing likelihood of dew formation. The air flow also moves warm currents up and out of the tube - whilst simultaneously helping to reduce primary cooling time. Hth  :)

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Emmanuel Marchal

Emmanuel Marchal

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I have an SCT and the dew shield works really great but if it is really humid dew will eventually form on the Schmidt face. I've taken on combining both heat strip and the dew shield. Not too hard to do. Below is the result. See the details on my blog post

http://skotworld.blogspot.co.uk/2014/02/dealing-with-uk-weather-dew-challenge.html

IMG_7617.jpg

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