Using lenses to create a beam of normal light??

If you had, say, light from a torch or whatever, directed it through a metal pipe or fiber optic to get it kind of directional, and then into some arrangement of lenses; what kind of maximum range could you expect before it completely lost focus? And would it still obey the inverse square law, or is that just for expanding spheres of light?

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SolarFlower_org (author) 8 years ago
110100101108 years ago
SolarFlower_org (author)  110100101108 years ago
That's pretty cool, interesting to see what just a single LED can do. It's still emitting from a point ish light source though... it'd be great to get this going with a 'extended' light source. ie, one that emits from an area.
get some loupes and glasses and experiment with it i think focusing the light source into a binocular (from the eye side) and focusing the binocular may emit a ray as wanted
kelseymh9 years ago
A perfect converging lens will produce a perfectly collimated beam only for the case of a point source of light placed exactly at the focus of the lens. If your light source is spread out at all, then you'll get a spreading beam coming out of the lens.

If you put your light into something like an optical fiber, as you suggest, you'll have very high losses, but the light coming out the other end can be an excellent approximation to a point source. So you could get a pretty decent beam with solid fixturing to keep the optical fiber and lens perfectly aligned.

Your comment about "completely lost focus" is misplaced. A parallel (collimated) beam is, by definition, completely unfocused. You've taken a point source at the lens focus and inverted it.
SolarFlower_org (author)  kelseymh9 years ago
If I was putting the light through a tube, so that coming out the other end the light was spread out and going all over the place, is there a series of lenses I could use to get it back to a point, or a column?
Depending on the tube, the light may or may not go "all over the place." With something like a cardboard tube from wrapping paper, there's a lot of scattering and absorption, so you get a dim output, with a spread of a few tens of degrees. With a fiber-optic cable, much of the light undergoes total internal reflection (to maximize the throughput), so at the other end it has a much larger angular spread.
SolarFlower_org (author)  kelseymh9 years ago
But if it was a wideish tube, can that be got back under control with lenses?
It still is dependant on, as Kelseymh has said, the material of the tube and what it is coated with inside; and some of it will be lost from absorption, and even atmospheric scattering (in a vacuum, it would not have an atmosphere to deal with, but that is difficult over long distances too).
SolarFlower_org (author)  Goodhart8 years ago
I was thinking of something with total internal reflection, otherwise not much useful would make it out the other end.
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