h a l f b a k e r y
Like gliding backwards through porridge.
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So, I have an idea that's also sort of questions I can't find the answers to.
I want to focus rays from the sun either using a large parabolic dish covered in mirror shards, or ideally through a large Fresnel lens and then direct those rays down the length of a circular tube with a mirrored interior
surface to create a portable solar cutting torch/kiln furnace.
Given a perfect lens, a perfectly circular tube and 100% reflection:
Will the rays pass through one another down the length of the tube and refocus at a distant point?
...and if so, would the same hold true for a bent tube? Could focussed light be redirected to distant points, say even underground?
...and why is there absolutely no information to be found on the reflectiveness of natural obsidian?
[pashute, Nov 01 2015]
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||Could you use a fiber optic instead?
||Why not use total internal reflection?
||Same principal I guess eh? but would the light rays re-converge after bending around corners? I try to visualize it, but it hurts.
||//Will the rays pass through one another down the
length of the tube and refocus at a distant
||You'll need a lens at some point. Think about the
point at which the parabolic dish (or Fresnel lens)
focusses the rays. They are arriving from all of the
dish/lens, and hence at all different angles.
They'll therefore bounce down the light-pipe at all
||For instance, a ray that comes from the centre of
the dish will travel straight to the focal point, and
straight down the middle of the light pipe (if it's
straight). A ray that comes from the edge of the
dish will enter the pipe at an angle, and will
bounce back and forth along the pipe.
||So, when the rays exit the pipe, they're going to be
heading in all different directions.
||And, as I recall from an earlier discussion here, you
can't focus light down to a point smaller than the
source - in this case the disc of the sun as viewed
||hm... I don't want to tighten the focus at all. Because the rays are at an angle to converge when they enter the tube, in my mind I saw them passing through one another at re-convergent intervals down the length of the tube. I get what you're saying though, the straight-line photon will get to the distant focal point slightly faster than the mid-mirror photon, which would arrive faster than the outermost... etc.
How about a variation of a Fresnel lens or reflector which, instead of bending concentric rings of light to a focal point, was designed to take the length and curvature of the conduit into account and scatter light accordingly. Could the topology of the lens/reflector needed to do this be figured out by algorithm?
and perhaps even morphed to adapt as needed?
||You can't focus light smaller than the source? I
thought it was you can't make it hotter than the
source... what if you collimate it first?