I guess with such dimensions, you're bound to get plenty of vignetting... and a very wide angle of view.
I used the Pinhole Designer (http://www.pinhole.cz
) to calculate it would give you a picture taking angle of 162?14'50"
(by the way, the program is freeware)
But on the upside, pinholes don't theoretically induce distortion in the image (but if your pinhole isn't round, it will)
Now, for the vignetting issue... lets do a bit of geometry
We all know light gets weaker the further it has to travel (inverse square law anyone)...
But lets not get into calculations but more into drawings.
Take a used sheet of paper, a ruler and a compass. Draw on the sheet your camera's size viewed from the side (side view of the film to one side, pinhole on the opposite). Put an X where the pinhole would be. Use the compass and draw a half circle in the rectangle with a radius the equivalent of the box thickness (pinhole to film distance) having its central point in the pinhole. Notice anything? The circle is very small in the center. This is where exposure would be evenly distributed. A large part of the sheet would be pitch black, but you would get an extreme wide angle.
Now do the same thing with a different size box. The results would be different. In extreme pinhole telephoto lengths, light falloff will be negligible if the film size is relatively small.
I hope the demo explains the workings of the camera more clearly... (at least, that's how I calculate the stuff)
You'll also get to understand why many like curved film surfaces (it minimizes the vignetting)