Re: Angle of ligh

Thanks Bill and Guillermo for your answers.

But ...

> Geometrically/mathematically speaking, the angle changes when the
> pinhole diameter changes, the change is so small tho, that in practice you
> can dismiss it. Since you want to calculate the "cone angle", otherwise
> known as "angle of view", here is a formula I just derived that takes the
> pinhole diameter into consideration:
>
> Cone angle = ArcTan [ (D+P) / (2 * B) ]
>
> Where"
> D = Diagonal of your film format
> P = Pinhole diameter
> B = Bellows extension (or focal length)
>
> As you can see, the effect of adding P to D is very small, i.e., for 8x10,
> "D" would be equal to about 325mm if you add to that a "P" of 0.5mm, you get
> 325.5mm, again, not a big change. The same happens if you change the
> pinhole diameter.

I'm not sure this is the answer to my question. If I could send a drawing
attached to the list it would be easier, but this is what I want:

I imagine a light entering the box/camera and forming a cone. This cone will be
independent of film size. I believe it will vary with pinhole diameter but maybe
not in a meaningful way.
Let's say I made a very long focal distance box, no matter the film size, and at
the end of the box, parallel to the pinhole plane usually is put the film. But
I'll be using just a fraction of the image formed by this cone, the rest will be
absorbed by the black walls of the camera box.
Now, what I intend to do is to place 2 sheets of film not at the end of the
camera, but at the walls that are perpendicular to the pinhole plane. I imagine
that the light absorbed by these walls will also form images, certainly
distorted (I believe someone in this list have already done that). How far from
the pinhole plane the film should be to be completely covered by light? My
imaginations tells me that if it is too close I'll have a "V" shape image.
Is this formula you sent me able to give me that info? I'm asking because it
takes into account the film diagonal and I believe this cone is independent of
the film diagonal, I'm not sure.

Sorry for this long post

Joao
Received on Tue Feb 12 11:42:33 2002