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Post by Deleted on Aug 6, 2014 20:13:56 GMT
Another update. After suffering from dewing the other night, I have made a heater to combat the problem. I have made a dew buster from resistors which will warm the glass plate on the sky cam. It consists of 8x 6 Ohm 1/2 watt resistors wired in series giving out 3 watts of heat using a 12volt supply. Under strict laboratory conditions and extensive scientific testing, (I turned it on) it raised the temp of the galss plate from 70degF to 83degF in 5 minutes. I have installed it in the cam and am awaiting some dew to bust. Installed in the housing. Only thing left to do is add a PWM controller.
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Post by Dragon Man on Aug 7, 2014 6:53:39 GMT
Well done Allan.
As you would know, the theory doesn't always match the practice.
The standard rhetoric for making home-made dew heaters is that the heater strap only needs to heat to between 1 and 3 degrees above ambient to prevent dew build up.
Yes, in theory that is correct.
But in practice it only works on small refractors and eyepieces due to their small glass radius. As soon as you try warm a lens over 120mm you will need to get the heater about 8-10 degrees above ambient to warm that much glass 1 - 3 degrees above ambient near its centre.
A large corrector lens needs even more!
If you are getting a 13 degree increase indoors that will be good. Because outside in the cold it may only get the glass 2 or 3 degreees above ambient, and that is perfect.
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Post by Deleted on Aug 7, 2014 11:36:38 GMT
Left it running all night while I tried to capture meteors. On checking the files this morning, the image was clear all night. Next test will be to let the glass dew up first then see if it clears it.
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Post by davy on Aug 8, 2014 20:44:09 GMT
looking into doing a portable all sky camera..been impressed by allans broadcasts ive watched. .im going to use a cheap spotting scope tripod and put my sammy on it..ordered shotgun cable today 15 mtrs so I can power camera from inside carols and sit in her kitchen with the laptop and osd menu remote. .
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Post by Deleted on Aug 8, 2014 21:35:19 GMT
Nice one Davy. Have fun.
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