On Mon, 31 Jan 2000, Jim Mallos wrote:
> The sun's distance from us is about 100 times its diameter. A 50mm focal
> length lens pointed at the sun will produce a solar image spot of the
> size you mention--- 0.5mm diameter. This is a focal length familiar to
> photographers. The widest aperture 50mm camera lens on the market is an
> f/1.0. In direct sunlight this lens will collect and focus about 2 watts
> of sunlight. (Note that if we try to pre-concentrate the light coming
> into the lens, we will only get a wider image spot).
Does this mean that when I used a magnifying glass to start wood on fire
I was using just 2 watts?
> Suppose we pick a 100 watt power rating, that scales us up to a spot of
> 2.5mm diameter. That sounds awful as a resolution if we are raster
> scanning, but it is not so awful as a minimum wall thickness if we are
> smoothly tracing the contours of a cross-section.
Are we going to be able to fuse more than thermoplastics, without going to
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