Re: [Phys-l] fire starter from the sun - revisited Once Again

[Brian Whatcott <betwys1@sbcglobal.net>]

At 07:29 PM 4/24/2006, LARRY w., you wrote:
> There is a lot of interesting development currently underway in the area
> of concentrated solar energy that may of interest to list members:
>
> <http://www.eere.energy.gov/RE/solar_concentrating.html>
> <http://www.nrel.gov/csp/>
>
> Larry Woolf


I also noticed through Mike E's patient ripostes, that the figure
of merit for burning glasses which I remembered so clearly,
  just aint so.
        The final para of this note:
 <http://photo.net/photo/optics/lensTutorial.html>
               reminded me to repent.

something like  D^2/ FL^2 would be closer to the purpose.
I see there is a transmittance or reflectance factor  useful to correct
 the numerator, and a trivial magnification factor affecting the denominator's
value using a factor very near one. It doesn't seem sensible to account
for the point spread function due to ablation of the target, that being
 rate and material dependent.


Brian Whatcott    Altus OK    Eureka!