light projection mechanism?

[YT2095]

sitting in my shed, in front of the Heater with the door closed listening to the radio, I noticed a shaft of light coming through the hole in my door (I use it keep an eye on the main gate).

 

this shaft of light was like a laser as my cig smoke passed through it, the spot on the opposite wall wasn`t really much bigger than the hole in the door, I examined it, the total distance was 1.75 metres from the spot to the hole.

I noticed that Around the spot I could see movement?

I looked through the hole and the only thing moving was clouds and a few birds.

I blew smoke at the spot and was astonished to find that it wasn`t a spot at all but very faintly it had perfect images of moving clouds AROUND it!

the further from the center spot the fainter it was, and you could see the occasional bird fly past too!

 

so I was wondering, is there some sort of relationship between how far something away is, as to how much the image spreads? and How does this actualy work?

 

and would a round hole present a better (non stretched) image, as the hole I have is rectangular and seems to stretch the "picture"?

I ecpect it`s similar to sitting inside a large pinhole camera, but I don`t understand the principal of it at all, just that it works.

 

thnx

[swansont]

A pinhole camera works basically because the hole screens out any nonparallel rays.

 

If you draw a ray diagram, you'd see that every point on the objects maps to only one point on the image, if the pinhole is infinitely small. It's not, so there will be some blurring. But if the object is far away, the blurring is minimal. You can see a diagram showing this here

[ecoli]

Small holes have a way of defracting light around it. A neat little experiment, especially for us glasses wearers. Take your thumb and forefinger and make a small hole, about 1/2 millimeter wide. Put it up to one eye, and close the other one. You should be able to see better, the image should be sharper.

[5614]

Small holes have a way of defracting light around it.

 

in this case it isnt technically diffraction because diffraction is bending of EM waves around an edge, which is caused by the wave nature of EM waves... in this case it is merely the 'pin hole effect' if that is what it's really called!