> from: Joe Gwinn <joegwinn@xxxxxxxxxxx>
> date: Mon, 22 Sep 2003 01:55:40
> to: olympus@xxxxxxxxxxxxxxx
> subject: Re: [OM] Nope, It missed it by few hundred miles
> For one thing, it takes from 4 to 40 photons absorbed in a
>certain period of time to render a grain developable, and the
>developed grain has about 10^6 atoms in it, whereas the above
>assumes that a single photon can expose a grain, which isn't
>true and cannot be true. Why cannot it be true? Because
>random thermal motion would then expose the film, leading to a
>hopelessly high fog level. Requiring multiple photons arriving
>within a short period of time sharply reduces the probability
>that thermal motion will randomly expose grains.
In my defence, I would point out that the photons involved are focused by a
lens onto an image receptor (film). By definition, therefore, if this system is
"sharp" and "focused", then all repeats of the two photons over time MUST pass
through the same points of the film. Therefore we just repeat the example 40
times.
>Nor are film grains ever "gray". A grain either develops or >not.
So digital photography is not new! You're quite right here, but of course
clumps give the grey - scale.
> Joe Gwinn
This effect may or may not be true. I read it. It made sense to me. I passed it
on. Probably badly and using some of the wrong terminology.
There is an alternative view which may or may not help, and which also may or
may not be "true":
In the case where light of varying spatial frequency strikes a film, we know
that the reflection from the film varies with temporal frequency. What would
make it vary with spatial frequency? Nothing I can think of.
Assuming this is true the light absorbed by the film is constant with spatial
frequency.
Light within the resolving limit of the film is absorbed by image - forming
grains.
Light outside the resolving limit of the film is absorbed by?????
And no, it doesn't all just sail straight through to the anti - halation layer.
Statistically SOME of it MUST strike grains.
Is this effect important? I don't know, and I'm beginning not to care. The
example was raised only to show that limits on resolving power of photographic
lenses are not new to digital. This can be believed or not as a question of
personal choice.
Julian
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