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Dew strips for secondary glue question

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#1 ColdNights

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Posted 30 November 2022 - 09:41 PM

I have seen the commercial type of dew heater pads that attach to the back of the secondary mirror for Newtonians.  The information just states to glue them onto the back of the mirror.  However, I cannot find what type of glue to use.  It seems to me that if they heat up then maybe the glue would let go.  A YouTube video a guy made his and used hot glue from a glue gun but his mirror back was not coated in black paint.

Does anyone know the glue to use? 

Also, the telescope has flat black paint applied to the back of the secondary, would the glue mess that paint up?

Thanks for any responses.

Jerry



#2 luxo II

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Posted 30 November 2022 - 09:45 PM

Silicone glue - so you can peel it off if you wish.

 

 

 and used hot glue from a glue gun 

Ok with quartz or pyrex but if it isn't the heat may crack it.


Edited by luxo II, 30 November 2022 - 09:47 PM.

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#3 KLWalsh

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Posted 01 December 2022 - 09:10 AM

Is dew on your secondary a real problem?

If it’s a closed-tube Newtonian, having dew on the secondary is unusual. Not impossible, just not common. I live in the very humid rainforest mountain region north of Atlanta, and I never get dew on my Newtonian mirrors. All of my Newtonians are closed-tube (cylindrical tubes).
If you have an open-tube strut-type Newtonian, getting dew on the secondary is likely, and you’d probably need a secondary mirror warmer. (The mirror just needs to be slightly above the ambient temp. It should never get hot enough to melt the glue.)

#4 wrvond

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Posted 01 December 2022 - 11:04 AM

I've experienced dew on the secondary and primary mirror of an XT10g I used to own. My solution for the secondary on that scope was this wrap around strip from R-Sky:

 

https://www.youtube....h?v=sgCJUP0Lq5c

 

I haven't had dew on my XT12i secondary yet, but I'm prepared for it - I installed a heater from Kendrick:

 

https://www.kendrick.../newtonian.html

 

 

The Kendrick heater glues to the back of the mirror. I simply used small dabs of silicone RTV to hold it in place. 

 

Even if the back was painted, the small dabs (doesn't take much) should hold it just fine and not damage the paint.



#5 ColdNights

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Posted 03 December 2022 - 08:33 PM

Thank you all for the input.  The new telescope is a 6” Sky-Watcher Quattro 150P Imaging Newtonian and I also have an old Meade TeleStar 4.5" Newtonian.  I live in the Deep South and yes the secondary will dew up sooner than the Primary even when you have a dew shield.  I have had the primary on the smaller telescope dew up also.  The smaller telescope I did my own resistors for dew heater behind both mirrors.  However, that ones secondary fits in a plastic housing not at all like the Sky-Watcher's secondary mirror.  Right now I have a dew strip wrapped around the Sky-Watcher's mirror's stem but I was thinking of making a string of resistors and putting them on the back of the mirror.  DewBuster web site has information on making dew strips from various materials and I have done some using resistors in the past and they work.

 

Thanks again,  




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