Cast Focused Shadow: Solutions and Tips

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Discussion Overview

The discussion revolves around the challenge of casting a focused shadow from an object onto a surface, specifically when the light source is positioned close to the object. Participants explore various methods to achieve a larger and focused shadow while addressing the effects of light source size and distance.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Nuno describes the issue of unfocused shadows when using a light source that is too close to the object and expresses a desire to find a solution that allows for a larger shadow while maintaining focus.
  • Some participants propose that the blurriness of the shadow may be due to diffraction effects related to the light's wave nature, though others challenge this by suggesting that the size of the light source is a more significant factor.
  • One suggestion involves using a smaller light source or a cardboard with a small hole to reduce the light's size, which may help in achieving a focused shadow.
  • Nuno reports success after implementing the suggestion of using perforated cardboard, resulting in a focused shadow even with the light positioned close to the object, although at the cost of reduced light intensity.

Areas of Agreement / Disagreement

Participants generally agree that the size of the light source plays a crucial role in shadow focus, but there is some disagreement regarding the impact of diffraction effects versus the characteristics of the light source.

Contextual Notes

The discussion does not resolve the underlying physics of shadow formation, particularly the roles of diffraction and light source characteristics, and relies on participant assumptions about these effects.

nununo
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Hi,

I have an object and I need to cast its shadow on a surface. The object is about 20cm away from the surface. When I point a light into it, if the light is too close (30cm), it casts an unfocused shadow. When I move the light away from the object, the shadow gets more and more focused. At 150cm the shadow is quite focused. But I would like the light to be very close to the object so that the shadow can be bigger. If I move the object away from the surface, its shadow gets bigger but it also gets out of focus.

I know that the light projectors in museums and theaters use lens. I also know they are ludicrously expensive. I tried using a simple lens in front of the light and somethings happened that suggest it may work with the right lens but I wouldn't know how to choose it.

Is there a cheap way to cast a focused shadow with the light close to the object?
Would using lens make it work? If so, how to choose the lens and the light?

Thanks in advance,
Nuno
 
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Well, the "blurriness" of a shadow is caused by quantum effects around the edge of the object, light is diffracted asa wave ehen it passes within a distance comparable to its wavelength.
 
_PJ_ said:
Well, the "blurriness" of a shadow is caused by quantum effects around the edge of the object, light is diffracted asa wave ehen it passes within a distance comparable to its wavelength.
I doubt that is the problem here, it seems to be blurred because the light is not a point source. Diffraction effects would not diminish by moving the light source farther away.

nununo, you need to have a smaller (in size) light source. Either use a smaller light source, or you could place a piece of cardboard with a small hole in it between the light and the object. This would reduce the amount of light, which may or may not be a problem for you.
 
Hi Redbelly98,

Your suggestion worked. I placed a perfurated cardboard in front of the light and now, even if I put it quite close to the object, the shadow is focused. I do have less light, but I think I can manage to find a solution for that.

Thank you so much!
 

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