So you have a camera that requires film to capture the image. How does it go from your camera to a picture sheet?
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The film is just a piece of plastic coated with a photosensitive(i.e., reacts to light) material. It’s basically transparent until light hits it and then it becomes opaque wherever light hit it, intensity translates to density of light/dark places (shading).
Because you’ve just turned the lighter parts to darker sections, the result is the opposite of what you want it to be, hence the name *negative*.
Once you’ve captured it though, you wanna keep light more light from reaching the still photosensitive material, so you open the film in a *dark room*, a room with little to no light, where you will deactivate the photosensitivity with a chemical process called *fixing*.
Once the negative is fixed you can shine a light through it to another photosensitive sheet, this one white instead of transparent so regular light can be reflected and show shades the way they were captured. Fix this second sheet, cut it to size and charge money for the service.
This second sheet you can pass through a lens and blow up or down the image to whatever desired size you want. The photosensitive granules are very small (under a micron if I remember correctly) so the resolution is pretty high, that’s how you could take a picture in film and blow it up to the size of a multi story building and not see any degradation.
For colour pictures, different granules are sensitive to different parts of the colour spectrum and so they shade differently. I don’t know if this is still the case, but colour film was composed of separate sheets all sandwiched together.
Source: my grandpa was a photographer and had a dark room in his bedroom. I spent a lot of happy days in there.
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