Old 01-05-2013, 01:25 PM #1
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Default wide beam laser

I am totally new to the world of lasers and would love some guidance on a new project of mine. I am trying to source a light/laser suitable for projecting a sharp silhouette onto a backdrop. I've tried using a stencil held over a normal light bulb, but I can't get a sharp image on the backdrop. My limited knowledge of lasers is that the light travels in a straight line which I hope will make a sharper projected image. I'm also guessing that a normal laser pointer would have too small a beam. So, is there such a thing ad a commercially available wide beam visable laser, or does anyone have a better idea of how to project a silhouette crisply on a wall. Any help would be really appreciated.


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Old 01-05-2013, 02:57 PM #2
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Default Re: wide beam laser

Easy, just get any random laser and defocus it. All lasers have a lens on the front to focus the beam, by twisting it you can defocus the laser. Doing it this way also means that you can use a much smaller stencil, as the diverging laser beam acts kind of like a microscope.

If you want to do this with light bulbs, you'll probably need to use an arc lamp or something similar with a smaller point light source.

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Old 01-05-2013, 02:59 PM #3
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Default Re: wide beam laser

Quote:
Originally Posted by matt bridges View Post
I am totally new to the world of lasers and would love some guidance on a new project of mine. I am trying to source a light/laser suitable for projecting a sharp silhouette onto a backdrop. I've tried using a stencil held over a normal light bulb, but I can't get a sharp image on the backdrop. My limited knowledge of lasers is that the light travels in a straight line which I hope will make a sharper projected image. I'm also guessing that a normal laser pointer would have too small a beam. So, is there such a thing ad a commercially available wide beam visable laser, or does anyone have a better idea of how to project a silhouette crisply on a wall. Any help would be really appreciated.
Basically any strong laser can do that, you just unfocus it from line to cone. It will still cast rather sharp shadows. If the laser is not focusable by design, you can simply add basically any lens in front of it to unfocus it.
Green lasers are most visible, and it would be obvious choice.
Anyway, even with normal lightsource you can obtain sharp projection. I think you've heard about the fact that when projecting movies on the screen :-)
The setup is basically like this:

(light source) ==== |mate screen with transparent picture, or stencil| ==== (convex lens) ============================ |screen|

The source picture or stencil should be roughly in focal point of the convex lens.
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Old 01-05-2013, 03:21 PM #4
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Default Re: wide beam laser

Thanks for the info. Can you recommend a shop in the uk where I can buy the bits I need?
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Old 01-05-2013, 10:06 PM #5
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Default Re: wide beam laser

You might not even need a laser to do what you want. A high-output white (or color) LED (such as a Luxeon), being both extremely bright and very close to a point source, should also work just fine (and at much lesser expense). If all you want is to see an image, why not just use a simple overhead projector?

Something else to consider - there is a phenomenon known as "laser speckle" which is associated with coherent light illuminating a surface. Visually it is an apparent "graininess" which may or may not show up in a photograph, depending on many factors. Here is some more info about it for your consideration:

http://en.wikipedia.org/wiki/Speckle_pattern

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Old 01-06-2013, 08:17 PM #6
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Default Re: wide beam laser

You can also just remove the lens, and the laser diode acts as a point source. You might want to try a simple LED instead (they're cheaper, safer, more difficult to kill, etc) - something without any optics/reflectors.
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