Re: Angle of ligh

Ribeiro,

I think "picture"s below help your thinking:
(Sorry for lengthy text.)

           v--pinhole
    _______ _________pinhole base
          / \
         / \
        / \ <--- image cone
       / \
      / \
     / \
    / \
   / \
  / ________ \ <----- film (nominal)
~~~~~~~~~~~~~~~~~~~~~~~ <---- film (big enough)

Light through pinhole forms image cone. On the film plane, image cone
forms cricular edge (image circle).

Usually film is a rectangular and utilize some part of image cone.

If film is large enough, all the part of inside of image circle fits
in the film. Image exposed film will be "disk" on rectanglar film.

Once you make film on the perpendicular walls like next "picture,"
             v--pinholea
      _______ _________pinhole base
            / \
           / \
          / \ <--- image cone
      | / \ |
film->| / \ |<-film
(b) |/ \| (c)
      | |
      | |
      | |
      +-------------+ <----- film(a)

image cone exposes not only film(a) but also film (b) and (c).
Image on (b) and (c) are distorted as you expected. Image on (a) is
normal.

****
I don't know how the angle of image cone is detemined. But I think
it is equal to 2xArctan(d/t) where "d" is a diameter of pinhole, "t" is
the thickness of pinhole-material.

If t is very small, d/t becomes very large, and Arctan(d/t) becomes 90
degree (2x becomes 180). So, pinhome-material should be thin for wide
angle image.

- Masaru

 
Received on Wed Feb 13 22:55:50 2002