Re: [ATM] The last public Star Party at Chiefland , Florida

["James Lerch" <jlerch1@tampabay.rr.com>]

----- Original Message ----- 
From: "Michael Lindner" <mikell@optonline.net>


> Russell Jocoy wrote:
>>      I have a question...   Does a primary mirror dew heater wrap around the
>> circumference of the mirror, or does it make an array on the back?? Do you
>> force warm air across the surface?
>
> I just blow fresh unheated air across the surface - that's been enough
> to keep dew off my primary so far. My secondary and telrad are heated
> and do need the heat.

This is the third year the 16 bino's went to Chiefland.   In a nut shell, it 
gets WET in Chiefland in November.  You know it's dewey when your have to 
squeegee off the LCD screen on the laptop to see scope.exe!! :)

The first year my Dew Control was a simple hair drier, which was a horrid plan. 
Within an hour of sunset the hair drier was being implemented.  Within two hours 
the hair drier occupied more time than observing.  By Midnight the constant 
cycling of the hair drier was causing power concerns for the imaging guys.....

The second year I had installed 4 new fans on the Bino.  A 4 inch 12volt fan for 
each primary, and a 2 inch 12volt fan for each secondary.  This worked out 
fairly well, but by midnight the hair drier was back out and being put to work. 
I seem to have had plenty of air flow over the mirrors, but they still dewed 
over.

This year I decided I was tired of fighting the dew and finally fixed the 
problem.  This year I built the "Dew Cell", an 18 point resistance heater 
network across the back of each primary mirror.  I took the existing 18 point 
mirror cell and just shrink wrapped a resistor to each support point.  The final 
result had 18 1k ohm resistors @ 12v (2.6watts) heating the backside of each 
primary with the existing 4" fans blowing ambient air across the front of each 
primary.

The secondaires this year were also treated to similar system.  Each secondary 
got 4 1k ohm resistors @ 12v (0.6watt) on the back side, and kept the 2" fans 
blowing across the front.  I also added eyepiece heaters to try and keep the 
eyepiece / tertiary assembly from dewing over.

I only had two problems with dew this year.  The first was dew DRIPPING off the 
frame of the OTA onto the primaries.  The second problem I had was the 
occasional dewing over of the eyepieces.

All in all, I am very happy with this approach, the only disadvantage is all the 
soldering required to assemble the 44 1k ohm resistors and the wiring harness 
(just shy of 100 solder joints!!!)  Here's a couple pictures of a primary cell:

http://lerch.no-ip.com/atm/Dew_Cell.jpg

http://lerch.no-ip.com/atm/Dew_cell_2.jpg

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)
http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"

" Press on: nothing in the world can take the place of perseverance.
Talent will not; nothing is more common than unsuccessful men with talent.
Genius will not; unrewarded genius is almost a proverb.
Education will not; the world is full of educated derelicts.
Persistence and determination alone are omnipotent. "
                                                           Calvin Coolidge 

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