Shining a light through a small hole.

[the tree]

My calculus lecturer mentioned in passing something about how shining a torch onto a screen via a small hole would create a series of rings of light (on the screen) that could be modeled as sinc² of the distance from the center (the lecture was kind of just about the sinc function, really). Annoyingly, he didn't mention what the effect was called so I couldn't read up on it.

 

Does anyone know what effect I'm talking about? What it's called? Why it happens? (I know nothing about optics, but this sounds kind of interesting)

[YT2095]

I`ve only ever made Projector "telescopes" that way.

no idea as to the name, although I could explain it on Paper drawing a few Diags

 

and No, I can`t do that on here, sorry.

 

you could try looking up Pinhole cameras though, that might give you a few good keywords to start a search from

[BenTheMan]

sinc is an elliptic function, right?

 

When you analyze the diffraction in one dimension, called Fraunhofer Single Slit Diffraction, you get a sine squared functions. Because sines and cosines are the one dimensional analogue of the elliptic functions, one would probably get the behavior you are talking about in two dimensions.

 

It happens because light is a wave, and the pattern that you see is interference at the screen between light that takes different paths to the same point. See the link that I posted, it has some nice physics there.

[the tree]

Turns out Fraunhofer diffraction was exactly what I was looking for. The Airy disc seems to be what he was describing, but the wikipedia article doesn't mention sinc in the mathematical details. Maybe I'll just ask him for more specifics some time.

[jian]

You can refer to the link about diffraction. http://en.wikipedia.org/wiki/Diffraction