(meteorobs) Colour camera advice for Sandia system?

Ed Majden epmajden at shaw.ca
Wed Aug 27 13:09:52 EDT 2008


Hi Chris:
	In B.C. especially on the coast we live in a rather high humidity  
zone and you require quite a bit of heat to keep the dome clear.  If  
you go to Jeff Brower's web page you can see the Sandia All-sky set- 
up!  See: http://members.shaw.ca/jbrower/sentinel/camera.html  This  
is the system designed by Sandia.  They did testing to see if the  
video camera could withstand these temperatures.  It seems to work  
fine here with the thermostat controller set at 100 watts.  You can  
see this in one of the pictures on Jeff's web site. http:// 
members.shaw.ca/jbrower/sentinel/camera.html
	I also operate some meteor spectrographs and keep dew from forming  
on the objective prisms or gratings by using a 30W or so resistor  
just below the lens element and grating.  I adjust the temperature  
with a variac until the resistor is warm to the touch.  In most cases  
this works fine but if humidity is really high I turn the variac to a  
higher level.  If I use a chopping shutter in front of the grating  
the temperature can be adjusted to a lower level.
	I think your fortunate to operate in such a low humidity area.  I  
would think that Kim Hay living in southern Ontario definitely needs  
more heat to keep her dome clear.

Ed Majden
B.C. Sandia All-sky Network

On 27-Aug-08, at 8:47 AM, Chris Peterson wrote:

> Hard to generalize. It really depends on your typical humidity and dew
> point. Here in Colorado (which is pretty dry), over the entire  
> state, our
> cameras stay free of dew and frost using nothing more than a fan  
> blowing the
> waste heat of the PC164C camera across the inside of the 5" acrylic  
> dome. It
> hasn't been necessary to add more heating. The domes do get  
> condensation
> (especially in summer when the humidity is up) if the little fans  
> fail,
> however.
>
> You only need to make sure the dome is fractionally above ambient  
> to avoid
> dewing. It should take very little power to do that. Consider that  
> antidew
> heaters for telescopes usually require only a few watts to keep  
> several
> hundred square centimeters of corrector surface clear, and that's  
> without
> active circulation. A small acrylic dome shouldn't have high  
> emissivity; I
> can't imagine any conditions that would require 100W to keep it above
> ambient. Do you actually use that, or do you just switch power to a  
> 100W
> heater, which typically runs with a very low duty cycle? I'd think  
> that if
> your average power is over a few watts, it suggests that the  
> surfaces around
> the dome are far too emissive.
>
> Chris
>
> *****************************************
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
>
>



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