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Friday, November 29, 2013

How does a digital camera work - Part 1

My dad asked me how a digital camera works the other day. He's a pretty smart guy and was once one of the leading industrial engineers in America. He was also a serious photographer in the film era.

Now, even he would admit that he's a little north of old and the rapid pace of technological change sometimes leaves him gasping as he tries to keep abreast of the latest developments. Oddly, this gives him a great perspective on the state of digital evolution. Instead of asking, "What's the latest? And where can I get it?" he asks "What's it good for? And what will it really do for me?"

So how does a digital camera work? What is a mega-pixel? And why do they come in so many shapes and sizes?

Today let's talk about analog photography. Which is to say film. Curiously, film photography is even more mysterious than digital photography. 

Film, as we would buy it from Kodak, is extremely fine bits of silver halide suspended in a gelatin layer that is spread on a clear plastic strip with holes punched down the sides. it's rolled up and put into little cartridges that you stick into a camera.

When a friend drops by and you want to take a snapshot you pull out the camera, point it at your friend, and press the button. The camera makes a quick adjustment for exposure before opening the shutter. The light enters through the lens and strikes the film. The process is a miniature version of the camera obscura or pinhole camera you might have played with when you were in school.

Now, this is where the mystical magic happens! When the light strikes the silver halide in the film something about it changes. What that change is nobody knows! It's been studied with x-rays, gamma rays, weighed, measured and still nobody knows. Some bit of quantum mechanics comes into play when the light strikes it but who knows what?


The answer comes when the film is developed. The silver halide that the light has fallen on turns to solid silver when the developer interacts with it. Those bits that received no light are not changed. The film is then put into a stop bath to neutralize the developer. This is followed by a swim in the fixer to wash away the undeveloped silver halide.

After the film has been rinsed and dried you have the familiar negative. Where the shirt your friend was wearing was white now it appears black in the negative because all of the silver halide in that area is now solid silver and blocks the light. Where she was wearing a dark hat now looks light because the silver halide was not developed and was washed away. So the light now passes through the film to look white. Thus, a negative is called that because it is the negative image of what you saw when you took the picture!

Enough for today - tomorrow we'll talk a bit about color. 

For today just remember that the image was created by millions of extremely tiny bits of silver halide reacting with the light to record the image of your friend.
 

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