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Dew Heater Position for Celestron 11" Edge?

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#1 BenKolt

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Posted 15 March 2016 - 11:13 AM

Greetings!

 

If the weather cooperates tomorrow night I will finally get to put my new Celestron 11" Edge through its first light / maiden flight.

 

I have a dew heater strap for this scope that I wish to use to heat the corrector plate.  This strap fits on the outside, and I'm not sure what the best position would be.  I've come up with three choices:

 

Position 1: At the very front of the scope.  The strap is directly heating the plastic and fits in front of the dovetail bar.

Position 2: Directly over the corrector.  Again, the strap is directly heating the plastic, but it would have to wrap around the dovetail bar.

Position 3: Behind the corrector.  Here the strap would directly heat the metal, but it could wrap through a gap between the dovetail bar and tube.

Position 4: Something else?

 

I've attached a picture (from the web) where I've added illustration of these three positions.

 

I've seen where others have placed a heater directly on the plastic ring that holds the corrector plate in place just inside the front of the tube.  Is this a product that is available for purchase, or are these home-made heaters?

 

I'd appreciate your comments and suggestions, particularly regarding what I have now, which is a strap that wraps around the outside.  But I would also appreciate alternative suggestions for a future configuration.  Thank you!

 

Best Regards,

Ben

 

P.S.  More information: my dew heater is a Dew-Not for 11" CST, and the controller is a standard DewBuster.  I have an aluminum Astrozap dew cover on order, unfortunately not available for me tomorrow night.

 

 

Attached Thumbnails

  • C11dewstrap.jpg


#2 mvas

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Posted 15 March 2016 - 11:28 AM

I use Position #3.

But I have full contact with the tube, 360 degrees.


Edited by mvas, 15 March 2016 - 11:30 AM.


#3 Richard O'Neill

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Posted 15 March 2016 - 11:38 AM

 I suggest an heuristic approach. 



#4 Jim Davis

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Posted 15 March 2016 - 12:10 PM

 I suggest an heuristic approach. 

I would use a Monte-Carlo simulation.


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#5 Uppie

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Posted 15 March 2016 - 12:39 PM

+1 for Position #3



#6 David_Ritter

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Posted 15 March 2016 - 12:51 PM

I've tried position 1. It worked very well to prevent dew but it also introduced warm air currents in front of the tube that messed up the star images.  So now the heater is in position 3 and is in full contact with the tube. Can't yet say how well it works, amazingly there has been no dew the last few times its been out.



#7 junomike

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Posted 15 March 2016 - 01:23 PM

Position 3 is correct.  The strap should be around the OTA and slid up to touch the Corrector housing.

The key to preventing any tube currents is to use as little heat as necessary (to dissipate or prevent the Dew).  IME this is usually low to med power.

 

Mike



#8 korborh

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Posted 15 March 2016 - 01:42 PM

Position 3



#9 BenKolt

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Posted 15 March 2016 - 01:52 PM

All:

 

OK, thanks all for the input.  Sounds like Position 3 is the way to go then.  I will be able to have contact 360-deg around the tube because the strap will slide between the dovetail and tube at this position.  I'm not sure yet, but I think the awaited dew shield will attach forward of this position, but that remains to be seen.

 

I forgot to mention that I have replaced the two little vents at the back of the scope with TEMP-est fans from Deep Space Products.  (I've had a lot of time on my hands while waiting for the weather to clear.)  I have read other threads where these help equilibriate the temperature and that, for most people, having them on all the time does not interfere with imaging.  If anybody has additional thoughts or concerns about these, please let me know.  I've wired them up so that they draw power from one of the DewBuster's 12V outlets.  This was handy.

 

Thanks again.

 

Best Regards,

Ben

 

P.S.  Regarding heuristic or Monte Carlo methods, I would be willing, but given just how few clear nights I've been having this season, I would't have an answer to my question until the year 2045 or so.  I'll rely on others' experiences vs. a random walk through dew strap position space ...

 

 



#10 Nitpick

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Posted 15 March 2016 - 10:04 PM

I put a heater in position #3 on my EdgeHD 11".  It does indeed pass between the dovetail and the tube and I get a full 360 degrees of contact.

 

I find that the single heater is not sufficient to prevent dew from forming on the corrector, however.  I augment it with an Aztrozap dew shield (both the aluminum one and the plastic one with the built-in heater strip)



#11 teleskopju

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Posted 16 March 2016 - 03:45 AM

I had mine on #2 but when I put it on #3 ie. on the white OTA body I had much better results.


Edited by teleskopju, 16 March 2016 - 03:45 AM.


#12 LouHalikman

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Posted 16 March 2016 - 06:23 AM

I am using a different approach, and I would like some feedback.  I have an aluminum dew shield attached to my C14HD tube. My scope is observatory mounted so I do not have to assemble and disassemble for viewing. My system has top and bottom rails.  It seemed that putting the dew strip over the two layers of aluminum was ineffective, so I have mounted it on the corrector housing itself.  Seems to work fine with very little heat required.  Lou



#13 junomike

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Posted 16 March 2016 - 01:43 PM

I am using a different approach, and I would like some feedback.  I have an aluminum dew shield attached to my C14HD tube. My scope is observatory mounted so I do not have to assemble and disassemble for viewing. My system has top and bottom rails.  It seemed that putting the dew strip over the two layers of aluminum was ineffective, so I have mounted it on the corrector housing itself.  Seems to work fine with very little heat required.  Lou

I'd still try to fit the Dew Strap in position 3 (between the top/bottom rails). I know with my XLT C14 It takes a little time, but the Dew Strap does fit between the OTA and bottom rail

 

Mike



#14 LouHalikman

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Posted 16 March 2016 - 08:12 PM

Thanks.  I'll give it a try.  Lou



#15 BenKolt

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Posted 18 March 2016 - 08:13 PM

Here's a follow up.  The clouds parted and I got to image over the past couple of nights!  I chose Position 3, and the strap did indeed fit between rail and tube with a little effort.  I had no dew issues.  I have also been informed that my dew shield is being shipped, so I'll add that to the mix next time for both dew and light shielding.  Thanks again for all the helpful suggestions.

 

Here's my first light post in case you are interested.

 

Best Regards,

Ben




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