Dew heater temperature

Ask your fellow astronomers to solve your telescope queries

Dew heater temperature

Postby EIZO » Fri Dec 08, 2017 1:30 pm

Never having used one before, I have connected up the dew heater and set a thermometer inside to check it

It reaches just above 86f 30c as far as my darkroom thermometer will go

just how warm should they be ?

Thanks


IMG_20171208_123321135[1].jpg
IMG_20171208_123321135[1].jpg (215.59 KiB) Viewed 650 times
Celestron Edge 8" Evolution, Esprit 120mm triplet, Sky Tee2, WO Binoviewers, 2" and 1.25" eyepieces, ZWO ASI 178MM camera, Neximage 5, Nikon D4s, D810, Nikkor 70-200 F2.8, Nikkor 14-24, Nikkor 70-200, Nikkor 24-120, Sigma 150-600 Sport
EIZO
 
Posts: 200
Joined: Sun Nov 26, 2017 9:09 pm

Re: Dew heater temperature

Postby dave.b » Fri Dec 08, 2017 5:43 pm

The purpose of the dew heater is to compensate for the radiated energy being lost from the front optical assembly of a telescope. Hence the temperature of the front assembly is a function of thermal energy input less thermal energy lost, i.e. radiated. You therefore need to use the dew heater to add enough thermal energy to keep the temperature of the front assembly above the dew point to avoid condensation. You can add more, but for little gain. In fact you might set up thermal air currents inside the OTA that impact on its optical performance.
dave.b
 
Posts: 797
Joined: Mon Feb 13, 2012 6:35 pm
Location: Staffordshire

Re: Dew heater temperature

Postby EIZO » Fri Dec 08, 2017 7:05 pm

Thank you easy when you know how :)
Celestron Edge 8" Evolution, Esprit 120mm triplet, Sky Tee2, WO Binoviewers, 2" and 1.25" eyepieces, ZWO ASI 178MM camera, Neximage 5, Nikon D4s, D810, Nikkor 70-200 F2.8, Nikkor 14-24, Nikkor 70-200, Nikkor 24-120, Sigma 150-600 Sport
EIZO
 
Posts: 200
Joined: Sun Nov 26, 2017 9:09 pm

Re: Dew heater temperature

Postby Aratus » Fri Dec 08, 2017 8:30 pm

It is actually the temperature of the lens/corrector plate which is the determining factor rather than the temperature of the strip. Measuring the temperature of the glass is not easy, so it's a matter of trial and error. You should always use a controller unit, and if dew has already formed, slowly increase the control until it gets rid of it. At first you might need to flick a torch on and off to check if the setting has got rid of the dew, but after a while it becomes instinctive. I know that in the summer it is enough to put it on the lowest setting. As autumn approaches it needs to be set to 1/4 increasing to 3/4 in winter. I tend to put it on a bit higher to compensate for higher humidity levels if dew is forming heavily on other surfaces. It does no harm to flick a red torch on and off quickly just to check the front glass from time to time.

As has already been hinted at, you shouldn't simply bung it on to full every time. It's a waste of power, and it might degrade your observation. I'm a fairly new convert to dew strips, (about 3 years) and I wish I had discovered them earlier!
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
Aratus
 
Posts: 722
Joined: Tue Jan 12, 2016 2:17 pm
Location: East Lincolnshire

Re: Dew heater temperature

Postby EIZO » Fri Dec 08, 2017 8:45 pm

Celestron Edge 8" Evolution, Esprit 120mm triplet, Sky Tee2, WO Binoviewers, 2" and 1.25" eyepieces, ZWO ASI 178MM camera, Neximage 5, Nikon D4s, D810, Nikkor 70-200 F2.8, Nikkor 14-24, Nikkor 70-200, Nikkor 24-120, Sigma 150-600 Sport
EIZO
 
Posts: 200
Joined: Sun Nov 26, 2017 9:09 pm


Return to Equipment Advice

Who is online

Users browsing this forum: No registered users and 1 guest