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!

 

[PJC01]

Hello Nuno,

Thank you for reaching out with your question about casting a focused shadow. I can offer some solutions and tips to help you achieve your desired result.

Firstly, it is important to understand the concept of focal length. This is the distance between the lens and the point where the light rays converge to form a focused image. In your case, the object is 20cm away from the surface and you want the light to be close to the object, but this results in an unfocused shadow. This is because the focal length of the light is too short for the distance between the object and the surface. Moving the light further away increases the focal length and results in a more focused shadow.

One solution to this problem is to use a lens with a longer focal length. This will allow you to keep the light closer to the object while still achieving a focused shadow. However, as you mentioned, lenses can be expensive. Another option is to use a convex lens, which is thicker in the middle and thinner at the edges. This type of lens can help to increase the focal length of the light without breaking the bank.

When choosing a lens, you will need to consider the distance between the object and the surface, as well as the distance between the lens and the light. There are online calculators and formulas that can help you determine the appropriate focal length for your setup.

In addition to using a lens, you can also experiment with different types of lights. For example, a spotlight with a narrower beam angle may help to create a more focused shadow. You can also try using multiple lights at different angles to create a more dynamic shadow.

I hope these solutions and tips are helpful in achieving your desired focused shadow. Remember to always approach scientific experiments with a curious and open mind, and don't be afraid to try different methods to find the best solution. Best of luck!

Sincerely,