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I've recently installed a Telrad on my C9.25 scope and immediately run into a problem - dew.

What products have you found work best at keeping dew off the glass plate?

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I would be interested to know people's ideas as well.  My telrad has been totally frosting over recently.  I considered bringing a small sheet to drape over it.

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I think they sell a dew shield for the telrad, not sure where though. But I did see it somewhere, maybe amazon?

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It is a problem I have too Michael, asked several stalls at IAS but nothing there.

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If you have power, stick a little resistor under the glass. Works a treat! I'll try and post a pic before leaving for work.

Or, for the more practically minded. Cut a couple of spare glass squares, keep them in your warm pocket. Replace as it Dee's up.  I think that this was Moonshane's idea.

Or, just wipe it with your thumb!


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Astro boot do a Telrad full length dew shield now and again. IMG_5273.thumb.JPG.12dfb367fe0035a7620b8ff9a3ec7092.JPGYou can also make one out of an A4 black foam sheet . Hold it on by sticky back Velcro.

I put in two small resistors in line linked to a dimmer 12v. Just slide under the slanting screen. There are also some pretty fancy Telrad dew heaters around https://www.telescopehouse.com/revelation-pro-telrad-dew-heater.html

If the dew is dripping , you might find transparency and observing hindered by moisture up above , time to retreat !


Edited by cotterless45
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I have the Astroboot version shown above, which is pretty good, but I still occasionally have issues with it fogging up.  I also have the Telrad version which came with one of my finders, but its more expensive than the options suggested above.


FLO also have a canvas cover by TeleGizmos that could be put in place when its not in use, but i haven't tried one of these.


The sheet of funky foam cut to the right size also works quite well.


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Thanks for details everyone's experience. I've plumbed for the Revelation dew heater. Relatively cheap and hopefully reliable.

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I secure a chemical hand warmer to the side of the telrad with an elastic band.   Works great.   Have been doing this for about 3 years now.


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I've got 2 telrads and four different dew control systems (I don't know how I got to this point, it is completely unnecessary).  Here's my take on them.

1. The official telrad dew shield that hinges and swings over... I don't rate this as very helpful as it is a bit cumbersome and doesn't really provide much cover. However I do find it very useful in that it has a dual purpose,  holding the mirror that you can get to reflect the view sideways so you don't have to do "finder-yoga" for high targets. This facility is great.

2. Wiping it - I try to avoid as it means getting fingers, gloves, etc wet and therefore cold.

3. Home made plastic shrouds made from plastic, sleeping mat material, etc. Works well, the longer and thicker the better.

4. A dew heater, I think I got mine from telescope house - a revelation product. This is great and is the set up on my vx14 - I can forget about dew and have a good time.


All my other set ups make do with approach 3 as I dont want the hassle of power and cables.

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Hi all, I have made many dew heaters for Telrads, I use a 2 watt 1% Metal oxide film resistor 10 ohm (bought off e-bay) run from a small battery box (also bought off e-bay). The battery box is for 2 x 1.5V AA batteries with an on/off switch. The resistor is mounted just beneath the Telrad glass and the battery box is vecro fixed to the side of the Telrad. The whole fitting takes about 30 to 45 minutes.

It's late now but I intend to drop a couple of photos to show how this works, anyone with a minimum of DIY experience can put this together.

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I had the same issue when I got my Telrad and made my own few shield for under £5. Posted about it here:

Hope that helps :) 

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Here’s my Heath Robinson ultra light version, idea borrowed off Cloudy Nights member Mark...thanks!

Cut out of a cardboard tube and painted black, so far so good and cost nothing apart from an hour or so of my time :)






Edited by jock1958

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I'm sorry for reviving this old thread.

WRT skywatcher58gb's solution, could you please let me know:

- how I could make precise holes in the Telrad body to let the wires through without the burnt-plastic smell?

- is there a recommended gauge of the wires used to run the resistor?

Many thanks,


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