Archived posting to the Leica Users Group, 2003/06/21

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Subject: Re: [Leica] Latent images
From: Eric Welch <eric@jphotog.com>
Date: Sat, 21 Jun 2003 16:48:57 -0700

on 06/21/03 11:15 AM, Martin Howard at mvhoward@mac.com wrote:

> 
> How is the latent image produced in films?  What is the mechanism?

For black and white, light strikes the photosensitive material. When it
does, the energy of the light changes the chemical structure of the silver
nitrate or whatever it is. And that's how the latent image is created.

If you actually want to see that latent image, latent meaning "potential."
you have to expose it to the developing agent. What has been changed
chemically by the light turns black. That which wasn't changed by the
exposure of light does not turn black.

Fixer is then applied to the film and it dissolves all of the material not
changed by the light, washing it away. That leaves only the material that
the light modified. Voila, the negative. :-)

Color is similar (especially Kodachrome), just more complex.

Eric Welch
Carlsbad, CA
http://www.jphotog.com

"I would rather see him burn the Flag and wrap himself in the Constitution,
than to burn the Constitution and wrap himself in the Flag."

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