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Dew has finally struck on the best night I've ever seen the sky. Advice needed


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Hey guys, I need some advice on an issue I'd never encountered before. Dew. 

So on Saturday I was testing out my new power tank i've spent the last 3 months building and planning (post to come soon), and as it was an exceptionally clear night I thought I'd image the Andromeda galaxy for the first time. All was not well to begin with, my PHD 2 kept messing up and it looked like my mount corrections were sometimes off the scale continuously. It took me about an hour of tinkering and calibrating to realise that closing and reopening PHD was all I needed to do as after that the mount remained relatively stable. I took my first light frame (1600iso 120s) of Andromeda and my god was it incredible, I was very excited. As my histogram was not central or anywhere I was happy with I reduced the next light frame to 800iso and then upped the exposure time to 5 mins. The image came out a lot worse, so I decided to up the iso back up to 1600 but keep the remaining time. I had literally no idea what was going on as I had never experienced it before.

I looked at my guidance system and it appeared to see the galaxy somewhat fainter slightly maybe but still on target so I know I hadn't drifted off to one of the neighbouring galaxies. I looked through my finder scope and all was well. No idea. So I relocated to Pleiades but this time I took my DSLR out. I shone my headlamp down the SW 200P and saw the primary was fine. But then I noticed on my Auto guider scope and my finder scope that their lenses were rather 'moist' But still my main OTA wasn't. I took my headlamp off again and looking down my main tube and shining my headlamp through the eyepiece I saw the culprit. My secondary mirror had so much dew on it, it was nowhere near clear. I assumed this was definitely the problem? But had nothing I could do about it.

So the question is, I need a solution to stop this from happening. I don't want to spend a tonne of money on this as it's nowhere near payday yet! I need a solution that can sort out my ota secondary from getting too moist plus also my other equipment. I've seen other people talk about dew bands and controllers, but I need this for 3 different scopes it may get costly.

I also found it weird how I started imaging last winter and never encountered dew at all until the other night! There is a star party my local Astronomy association is pulling for the public in two weeks and as my scope has been deemed reserved for observing to the public, I'd like to have a solution before then just in case my scope fogs up during that show!

I have a powertank with 3 12v outputs and USB sockets which is about 3 meters from my scope at all times so I could use that to power anything I need.

Any night is a good night if you learn something, whether it's a good or bad thing :p

Any suggestions please? DIY is fine!

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Hi,

I has a similar experience a week or so back. Maybe some of these comments could help you too :-)

I spent some time at the weekend making dew shields out of a camping mat. If the cause was dew hopefully this will help. I suspect in my case it was more likely to be river mist.

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Prevention, prevention, prevention!  :icon_biggrin: Preventing dew, in the main, is easier than removing it after it has formed. There are several commercial and DIY solutions to this. A 12v hairdryer can be pretty handy as well in an emergency.

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I made a secondary heater for my 10”. A bit like this.

http://www.dewbuster.com/heaters-330ohm-resistors.html

I’m not a diy person so it’s not too difficult. And surprisingly it works very well. :) 

Here’s a pic. Wires run along the spider veins. The copper & resisters are bare on mine, it was quite a tight fit but I managed to squeeze them behind the secondary without removing it which was very pleasing.

4C822B55-050E-424D-A31B-BFCC58FD1530.thumb.jpeg.b9d3105e85791bc597b0f09c2cdc93dd.jpeg

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Thanks for all the advice guys. I'm now ordering my own parts for the controller. Not sure I could trust myself with the heater strips yet, I reckon I'll mess it up somehow. I have recently though created myself a dew shield. I have heard some people say they aren't that effective on newtonians however I also have a neighbour who loves to have their security light go on and off every so often so this will help out with that also. Only cost me a couple of quid to make. Also got leftover bits so may make some for my finder scope and also maybe my other refractor. You can see how great the felt is at absorbing the stray light too. Sorry the pictures are of low quality, my house lights are very dim.

 

 

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