Where to put dew band

[dark knight]

Hi all, really struggling with where to position front element dew band heater. Telescope is an esprit ed120 pro, the problem is the built in dew shield means the dew band is some 5 inches away back down the tube from the front element glass which after half an hour is still fogged up, any ideas?

[dark knight]

[Neil H]

Hi I have the bresser 127 with built in dew shield like your I place my strap around the dew shield so it's just in front of lens element so in your pic it will be half way down the dew shield 

[dark knight]

I'll try that thnx, i think its the inner glass that is more problematic with mine though as its a triplet

[Waldemar]

Carl, it is nearly impossible that the inner glass of your telescope fogs up...
As Neil said, attach your dew strap around the dew shield and it will work fine.

 

[dark knight]

Hmmm the fog was definately on the innermost glass surface, maybe some damp has got inside the tube and caused the fogging? Going to order a 2 inch dessi cap to see if that will remove it, only other thing i can think of is to use a hairdryer on low heat and put some warm air inside the tube and see if that helps dry it out, open to suggestions first of course. Also there seems to be a severe difference in opinions on where to put the dew band, some saying on the dew shield is a waste of time as it needs to be behind the front element directly on the ota, the dew shield doesnt sit tight against the ota and therefore doesnt transfer the heat to where it is needed

[teoria_del_big_bang]

2 hours ago, Neil H said:

Hi I have the bresser 127 with built in dew shield like your I place my strap around the dew shield so it's just in front of lens element so in your pic it will be half way down the dew shield 

I also had this same question a couple of years ago and came to the same conclusion that this is where it works most efficiently.

So far I have not had any issues with dew.

Steve

[dark knight]

On the esprit ed120 there is a 5mm air  gap between the dew shield and the glass elements/cell so can understand why putting the dew band on the dew shield wouldn't necessarily be the most efficient place

[sn2006gy]

I have the Esprit 120 and i have mine just in front of where yours is. Instead of behind the dewshield, just right in front of the dew shield screws.  I found it worked well there. People swear by both,  i'm not sure the dewnot has enough oomph to heat the entire lens cell but it seems to have enough power to keep it dry just in front of primary lens.

[Synchronicity]

I have the Esprit 80 and my heater is positioned alongside the lenses with the aim of keeping the glass warm.  My thinking is that if the dew shield is colder than the glass then it will collect the dew and the glass will stay clear.  Ive had this out for over 10 hours each of the the last 2 nights with temperatures at or below freezing and everything iced up by the end of the night but the glass has been clear throughout.

I use a CooWoo lens warmer from Amazon.  About £15 and runs from a USB supply.  Cheap and effective.

All the best

Michael

[Waldemar]

The purpose of a dew band is not to heat the glass, but to warm the air in front of the glass just a few degrees, so the relative humidity of the air will be lower and moist wil not precipitate on the glass.

Edited January 3, 2021 by Waldemar

[Waldemar]

56 minutes ago, dark knight said:

Hmmm the fog was definately on the innermost glass surface, maybe some damp has got inside the tube and caused the fogging? Going to order a 2 inch dessi cap to see if that will remove it, only other thing i can think of is to use a hairdryer on low heat and put some warm air inside the tube and see if that helps dry it out, open to suggestions first of course. Also there seems to be a severe difference in opinions on where to put the dew band, some saying on the dew shield is a waste of time as it needs to be behind the front element directly on the ota, the dew shield doesnt sit tight against the ota and therefore doesnt transfer the heat to where it is needed

The only way that can happen is when you take the cold scoop into a warm room. It always needs time to warm up slowly, better still put it in a place with outside temperatures like an unheated shed after you used it.
The way to get rid of the moist inside the OTA is to leave it open, so without an eyepiece, so it can dry out. No harm will be done.

[dark knight]

Telescope is kept outdoors on its mount, under 2 telescope covers. The fogging on the internal glass is just like when you have to de-mist a car windscreen

[dark knight]

I do leave the imaging dslr attached so maybe i should remove it at the end of each seesion

[Waldemar]

The warmth of the sensor cause that maybe... I never had any of my telescopes fogging up on the inside, but I don't use a DSLR, only on holidays.
Kind of a weird problem... but there is always something to learn...