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



At 08:00 AM 4/16/2006, you wrote:
I can understand why the diameter of the lens in important, the
larger the area, the more energy focussed, but I don't really
understand why the focal length would play such a large role. It
certainly is part of the f-stop formulation, but I don't see how it
could have a large impact on fire starting. Care to explain?

cheers,

joe

Joseph J. Bellina, Jr. Ph.D.


In the Socratic manner:
It is possible to choose a lens which gives a small image of a scene, or a large
image. Which sort of image would portray the image of the sun as smaller?

Supposing that the effective Solar energy density is 700 W/m^2
would a large diameter lens, or a small diameter lens pass more energy?

One would want a lens which passes more energy, and one which provides
the smaller image, you may have concluded.
What common lens specifiers does this conclusion lead one to advise?



Brian Whatcott Altus OK Eureka!