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



I don't understand the conduction problem. I think a smaller image has a smaller circumference thru which to lose energy. A one micron image would raise the temp. greater than a mm diameter one; ttbe being the total energy.
Further: depending on which aberration(s) are important, I suspect this is another factor to select. OTTOMH, I'd pick a shape * w/ the least aberration, i.e. plano-convex w/ the vex side facing the image.

* not to mention acromats, non spherical lenses, etc.


bc, imagining an f/ 0.001 short focal oxidizing the atmospheric nitrogen.

jbellina wrote:

Aha, so there are two issues, the size of the lens, since the larger the lens the more energy collected, and the size of the image formed, since the smaller the size, the more concentrated the energy. There is also John's point that if the image is too small, there could be conduction problems.
I'm beginning to see the light!

cheers


Joseph J. Bellina, Jr. Ph.D.
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556

On Apr 16, 2006, at 11:24 AM, Brian Whatcott wrote:


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


cut