So you have a camera that requires film to capture the image. How does it go from your camera to a picture sheet?
Here is my attempt at this.
Ever carved/wiped and image on a fogged bathroom mirror or a car window with condensation? Same kind of principle but backwards.
When you take a picture with a camera with file. Light enters the lens and carves “clear” spaces on the film. Where there isn’t light (i.e. an object/person) there is no light so the film (fog) stays creating dark areas. When the film is processed the light areas (no objects) are washed away. Only leaving the dark areas (objects).
This is just black and white images. How you get color is to separate black and white into Red, Green and Blue. But the principle is the same, you just have three colors instead of two. This creates the effect of full color to us.
The exposed film and special light is used to expose photo paper to the image. Then the photo paper is treated with chemicals to cause the exposed parts of the paper to change and the image ireveals itself. During these processes the film turns into, or is transferred onto a negative and that is usually included with your photos. The negatives can be used to make more copies of the photos on photo paper.
SmarterEveryday did a good walk thru of a small scale film processing lab and I’m sure others go thru the process on YouTube if you want further detail. The American Innovation podcast did a great series dramatizing the events of how the modern film camera came to be.
So, film has a coating on it that contains tiny grains of silver that are chemically sensitized to light. When you take a picture, those grains are “hardened” (not actually hardened, but the chemistry gets pretty complicated to describe it accurately) based on how much light they were exposed to. More light = more hardened grains in that area.
So, you finish your roll, then it has to be developed, which does three things: it turns the hardened grains dark, it washes out any unhardened grains, and it stops the silver from being sensitive to light any more.
Then you have a negative. Areas that got more light are darker, less light are lighter, and everything in between.
Then, it’s more of the same.
You project that negative through another lens onto a sheet of paper coated in a similar silver-bearing material, and the whole process repeats: areas that get more light turn darker, areas that get less light stay lighter (remember how the brightest areas of the negative turned darker?). Develop that paper much the same as the film, dry it, and presto: a printed photograph.
Color is basically the same, just with multiple layers of coating that have dyes to block specific colors of light from getting through particular layers, and the same deal for the paper.
1. You wind up your film inside the camera so it’s in a light tight spool, you take that out of the camera.
2. You go into a black room (zero light including red). You have to take out the film from it’s canister, thread it on a ring/spool that spaces it out so no layers touch, put it in a light tight container that has some holes in it.
3. Soak said container in various chemicals that set the film so you can take it out in the light.
4. Acquire dark room (red light)
5. Do you know the old school overhead projectors? You’d have a transparent sheet with words in it that you’d project on a screen. Developing pictures is like that but small. The light is projected through the film and down on to light sensitive paper. Based on the amount of light that gets through the film that darkens the paper to create the same image. If it’s projected closer to the paper the photo is smaller, further away to be bigger. There’s more technical stuff about focus and whatnot, but that’s the gist of it.
6. Then the light sensitive paper needs to be soaked in various chemicals and dried so that it sets and can be taken into the light.
That’s the old school manual process for it, they do have machines that do that too.
I don’t really know about color, but for black and white
You got this crazy goo on some paper that just changes when light hits it. The more light that hits it, the more it changes. The more it changes the more it holds onto the paper. After you take your picture, the paper has different spots of lots of changed goo and very little changes goo, so we wash away the goo that hasn’t changed, leaving a more hardened goo where the light hit. If you look at the paper (which you can kinda see where the old goo washed off because it’s kinda see through) you see dark spots where lots of light hit and see through spots where light didn’t hit so much. But its all backwards! That’s okay. Take the kinda see through paper now and put a light behind it. The light goes through the see through parts and the darker parts where the new crust goo formed cast shadows. If you lift the light and the funny paper, you cast a really big shadow. Now get some special paper that you can only open in your special room with its special lights and you can put the special paper in the “shadow” you just made. Mess around with how much time to leave the light on to cast the shadow, and now, your special paper has changed. Where there was light, the paper will get darker. Where there was shadow, the paper will at white. BUT you can’t see anything… yet. Put the paper through some nasty smelling trays and you will actually be able to watch your new picture appear on the page.