How does a film camera work?

Demystifying the process of writing with light and the chemical romance of film

Take a break from taking selfies to consider how the granddaddy of cameras works. We’re talking about the good ol’ film camera.
A camera basically consists of a lightproof box that lets in a bit of light at just the right moment. Once the light enters the camera, it creates an image by causing a chemical reaction on photo film.

Let’s imagine you’re taking a picture of your dog playing in the snow. As you see your dog running toward you, you lift the camera to your eye. Outdoor light reflects off your dog, bouncing into the camera, through the lens and onto a mirror. The light then bounces off the mirror into a five-sided piece of glass called a “pentaprism” and into the eyepiece.
Finally, the light passes through the eyepiece and into your eye. This allows you to see the image exactly as it will appear on film. As you hold the camera to your eye, you wait for just the right moment. Your dog stops for just a moment. Snap!
What’s happening inside
When you press the button on a camera, the mirror flips out of the way. Light then passes onto the back of the camera where it hits photographic film and starts a chemical reaction.
When you click the button, you instantaneously record the reflected light off objects in the camera’s field of view. Though you probably can’t tell, film consists of a thin sheet of plastic coated with tiny silver crystals in a gelatin. The crystals react to light that passes through the camera and onto the film.

What is film made of?
The film is covered in an emulsion, made up of silver halide crystals, that will capture the image when exposed to light. When the camera’s shutter opens for a fraction of a second and light passes through to the film, the silver halide crystals turn into silver ions. The density of the silver ions, compared with the remaining silver halide, represents the intensity of the light in that area of the picture.
Dark room
Once you’ve captured your photo, it’s time to develop the film in a darkroom. The development process involves dipping the film in several chemicals. Special chemicals called “developer” help the image become visible.
If you have ever held developed film up to the light, you may notice that something looks strange. Developed film gives you a negative image!
Negative and positive
This means dark objects will look light and light objects will look dark.
When it’s time to print your photo, you must shine a light through the negative film. This creates a shadow on special photosensitive paper, leaving an image that is the opposite of the negative — a positive print! At last you have your photograph.
Processing the Film
Turning the exposed emulsion into an image requires using both chemicals and time. First, the film is placed in a developer solution, which converts the ions into black silver. The film is then placed into a fixer, which removes the remaining silver halide crystals, leaving just the dark silver in place. After the film is washed and dried one last time, what’s left is called a negative because the film is dark in areas that recorded the most light, and it’s white in areas that received no light. Photo developers will then pass light through the negative and onto photographic paper, where the light levels are reversed and the end result is the image that was in front of the camera.
But what about colour pictures?
Instead of just one layer of emulsion, as in black-and-white, color film has several layers, each emulsion recording a different color. Between the emulsions are protective interlayers and all of these layers together aren’t as thick as a human hair. That gives you can idea of the care needed to make color film — and the delicate handling needed to process it properly.


Photo credit: Lis Bokt 


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