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Heater on Secondary

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#1 scoping

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Posted 25 June 2014 - 06:58 AM

I see claims that the coating on a secondary mirror can change the figure so what happens when you glue a heater to the back of one.

#2 scoping

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Posted 25 June 2014 - 01:23 PM

Wow 47 views and no responses. I find it hard to believe that no one cares especially with all the concerns of mirror accuracy and optical alignment. Or is it no one knows what happens? Maybe one of our expert opticians will chime in.

#3 Brian Carter

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Posted 25 June 2014 - 01:39 PM

I had this on my secondary for years and never had a problem with it. Supplied just enough juice to keep the dew off.

https://www.astrosys....biz/dewgrd.htm

#4 scoping

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Posted 25 June 2014 - 01:58 PM

[quote name="Brian Carter"]I had this on my secondary for years and never had a problem with it. Supplied just enough juice to keep the dew off.

https://www.astrosys....biz/dewgrd.htm [/quote




Is it resting against the back of the mirror or are you using adhesive.

#5 Brian Carter

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Posted 25 June 2014 - 05:11 PM

I'm not sure what in using, been a while since I installed it. Probably I used silicone glue. Astro systems supplied directions with the unit, I would have done whatever they said.

#6 scoping

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Posted 25 June 2014 - 08:18 PM

Its hard to believe that with claims of coatings changing the figure of a secondary and no one is concerned what happens to the figure when you glue a heater on the back of one. What happens when you cram all that cotton batting in behind all of that? Its kinda crazy people spending extra money for a 1/20 to 1/30 wave secondary then gluing a heater on the back without any second thoughts. :question:

Has anyone ever tested a secondary before and after a heater has been glued into place? :confused:

With all these claims of super mirrors being turned out and concerns of perfect alignment of optics but we are not concerned about possibly ruining the figure of that $300.00 1/30 wave secondary.

Where are all the experts that respond here ever day and no one has chimed in with some facts, what gives did everyone go on vacation at the same time?

#7 scoping

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Posted 25 June 2014 - 08:25 PM

I'm not sure what in using, been a while since I installed it. Probably I used silicone glue. Astro systems supplied directions with the unit, I would have done whatever they said.




I have the same unit on the back of my secondary, maybe a call is needed to see if they have done any testing to see if gluing that unit changes the figure of the secondary mirror.

#8 gpelf

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Posted 25 June 2014 - 08:36 PM

The heating element and the cotton is such a small mass compared to the secondary substrate, Would it even effect anything? Not sure myself. :question:
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#9 gpelf

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Posted 25 June 2014 - 08:48 PM

I see claims that the coating on a secondary mirror can change the figure so what happens when you glue a heater to the back of one.


IIRC, The figure change from coating is due from a non-uniform surface at the optical wavefront, not necessarily strain in the glass due to coating...
Greg

#10 choran

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Posted 25 June 2014 - 08:51 PM

I'm no expert, so not responding to that call. I removed mine from a 2.6" secondary simply because dew wasn't really much of an issue where I live, so I very rarely used it. Truthfully, I can't say I noticed any difference before/after in terms of the image, and mine had been affixed with quite a bit of adhesive--took a good bit of time to remove it all.

#11 scoping

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Posted 25 June 2014 - 08:56 PM

I see claims that the coating on a secondary mirror can change the figure so what happens when you glue a heater to the back of one.


IIRC, The figure change from coating is due from a non-uniform surface at the optical wavefront, not necessarily strain in the glass due to coating...
Greg


Well that makes sense and thanks. But my question still stands about gluing a heater on the back of the secondary and stuffing cotton batting behind all of it.






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