Cast Focused Shadow: Solutions and Tips

[nununo]

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

 

[_PJ_]

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.

 

[Redbelly98]

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.

 

[nununo]

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!