Re: [APML] How much power for dew heaters?

[Mark Kaye <mark.kaye@sympatico.ca>]

>Let's say I'm going to use 4W for a 70mm objective. For a 140mm lens, should
>I be using 8W or 16W (4x as much area), or maybe even more because it's
>harder for the heat to reach the middle of the lens? Absolute values aren't
>really interesting at the moment because I'm going to choose one fixed value
>for each heater and build a controller with a variable output so that the
>heating can be regulated. So I'm only interested in relative values right
>now.

    I use five watts on a 13cm refractor with a dew shield and that is 
usually enough.  Rarely will I have to crank it up to ten watts.  The 
important thing about dew heating is to turn it on when you start to 
observe and leave it on.  If you try to get rid of dew once it starts to 
form, then you will need twenty or thirty watts and be fighting a loosing 
battle.
    Clear skies!
                MK

http://www3.sympatico.ca/mark.kaye/


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