Re: New site pinhole

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>

> If this is true, then I'm going to need to abandon the camera I'm in the

Stop, don't abandon it! keep reading bellow.

> middle of building and start over, so I hope someone will confirm this.
> I was going by the formula that says that the image circle=focal length
> x 3.5, so thought I was in good shape, but my focal length is only half
> the radius of the inner circle.

[paraphrasing] what was said was that a camera of the type in question
having "6" pinholes equidistant from each other has to have a focal length
of "at least" the radius of the inner film plane cylinder. That does not
mean you can not make cameras with smaller focal length, like yours, which
has only half the radius, it only means you would have to have more pinholes
around the outer cylinder, how many? well, for that we'd have to make use of
some math. In your case (half the radius focal length), I'd say that 8
pinholes should suffice (1 every 45 degrees).

The 3.5 factor you mention, has been mentioned only in the context of FLAT
film planes. A convex film plane present more challenges for light,
meaning, light fall off occurs faster than in a flat film plane. The factor
for a convex film plane would not be a fixed number (lineal), but a
variable, in itself function of the focal length and the inner circle
radius. Math and other explanations available upon request.
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Received on Sun Dec 19 21:17:52 2004