h a l f b a k e r y
Like a magnifying lens, only with rocks.
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One problem with permanent solar magnifiers is that the lenses get dirty. Then when you wash them, they get scratched. The fly eye water lens uses multiple small drops of water together in a large array patterned after a fly's eye.
A hanging droplet of water in the sun can focus the sun's rays to
a point, just like a magnifying glass. However the energy focused is only the amount which strikes the droplet. I propose that a large screen with many holes be devised, such that each hole would retain a drop of water when dipped. I am not sure if the drop would have to hang within the hole or could encompass the entire hole.
The screen is slightly curved so the light focused by each drop converges on a point - the same as any solar concentrator. Put a hot dog there! The lens can be cleaned and renewed by dipping the whole screen in water.
Low-Power Liquid Lens
This involves two drops of water, not one, and deals with the problem of changing focus with little energy. But it shows that the basic technology exists. [jutta, Nov 20 2008]
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||So, all you have to do is to devise a frame that makes a water drop focus at a point, at a usable distance, at an angle to the light, and makes the drops around it do almost the same thing, but exactly different? I can almost smell the fish cooking now.
||I read long ago about a group that was making hollow plastic lenses and filling them with water.
||Interesting variation. Each drop would need to be quite flat, compared to a drop of water on a flat surface. That means a surface tension modifier might be of use, but then it won't be pure water. The shape of the drop would need to be controlled simply by the diameter of the hole. At the moment, I am not sure if it can be done correctly.
||Spinning off on a tangent (pun completely intended), a perfect parabola can be made by steadily rotating a container which has been filled with water. Remember the parabolic pool table? Unfortunately, this only works when vertical.
||Is this related to the idea of hanging a bunch of baggies of water from trees in the forest to start a campfire?
||Uh. Has anybody confessed to that, yet?
||//Put a hot dog there// Or for ironic effect, a fly!
||I am intrigued by the baggie of water in the tree idea. I have tried to burn paper using a 2liter pop bottle full of water, but no go.
||I suspect it would be bakeable if you
had a curved (shallow parabolic) sheet
of some hydrophobic material (eg,
polythene or teflon) with perforations of
the right size. Water would sit in the
perforations but would bulge out to
form a "lens element"; the larger the
hole, the flatter the lens element. With
the right geometry, you could get all
the lens elements to focus at a common
point as you
curvature of each lens element (and
hence its focal length) would depend on
the surface tension of the water. This
would be *very* sensitive to any
contaminants, so you might find that
your lens only worked with (say) pure
However, the idea
itself is utterly brilliant, so [+]
||Jutta's anno brought this old one to the surface. I think I have seen flexible brass screens with honeycomb-patterned holes. Maybe something like that could be used? As re the hydrophobicity one could grease the thing up with a can of Pam or WD40.