Film and Digital Cameras: How do they work?
Photography, arguably one of the most important inventions in history, is a lot more complex than the click of a button. The first photo took more than eight hours to generate, and it was still blurry. With today’s technology, we can create sharp images in milliseconds. What is the science behind photography?
There are two main types of photography: digital and film. Twenty years ago, the majority of cameras were used with film. However, as digital photography was introduced, prices went down, and quality went up, and most commercial and industrial applications switched to the digital form. The two have similar processes. Light is focused on one point using the lens, but the process of image conversion is where the two main types of photography differ. In a film camera, the film absorbs light and creates an image, while digital cameras use sensors.
Generally, light can be focused as a wave but its energy is distributed in packets called photons. These photons contain energy that is read by chemicals on a film or pixels on a sensor. A standard film and digital camera have mostly the same parts: The camera body and the lens.
The optical part of a camera is the lens. At its core, camera lenses are composed of a curved piece of glass that focuses the light that enters a camera (1). The lens bends the light in a specific way that allows the camera to focus on an object or a scene. This technology works because light moves slower through glass than air (1). Therefore, when one side of the light wave hits the glass, it slows down, and the other side goes faster, causing the wave to bend. You can compare this to a moving shopping cart hitting grass and how it bends (1). The same thing happens when the light exits the glass because part of the wave exits first and then speeds up. This lens focuses all the light rays to a single point, creating a sharp image. These points create a real image that looks just like what is in front of the lens. When the light rays do not condense to a point, the picture is blurry. Therefore, to focus a camera, the user moves the glass piece closer or farther to the film or sensor.
However, the camera body and the lens differ when it comes to what captures the light. Film cameras use film, which utilizes chemicals to record the details and patterns of the light (2). The film is composed of an emulsion of silver halide crystals, light-sensitive grains spread on top of an acetate base. When silver halide crystals are exposed to light, a chemical reaction occurs. The light ionizes the halide ion, causing it to release an electron and give it to the silver ion. This reaction reduces the silver ion into silver metal (6). The more light that goes through the camera, the greater the reaction of the silver halide crystals. In black and white films, more light produces a darker opaque on the film, while less light produces a transparent area (3). This process creates a negative image, where black and white colors are inverted. Once the image is developed, the silver ions are removed leaving only silver metal.
Colored films are more intricate. They also have silver halide crystals, but there are three layers of emulsion, with red, blue, and green light-sensitive dyes mixed in. Once the film is developed, the halide crystals are removed (3).
Sensors in digital cameras require different technology. Unlike films, sensors have millions of red, green, and blue pixels. When light hits the pixel, the sensor traps the energy and an internal computer reads how much energy is produced. Reading the amount of energy a pixel contains allows it to estimate which ones are light and dark. Each pixel also has a color value, so they can estimate the color based on what nearby pixels are registered.
Photography is a remarkable fusion of art and science. From its humble beginnings of eight-hour renderings to nowadays instant, sharp images. Using lenses to bend light perfectly and films and sensors that convert photons into a tangible record, photography bridges the gap between fleeting moments and lasting memories.
Citations
- Harris, T. (2001, March 21). How Cameras Work. HowStuffWorks; HowStuffWorks. Retrieved from https://electronics.howstuffworks.com/camera.htm
- CreativeLive. (2018). How Does A Camera Work? CreativeLive. Retrieved from https://www.creativelive.com/photography-guides/how-does-a-camera-work#:~:text=A%20camera%20lens%20takes%20all,they%20create%20a%20sharp%20image
- Cianci, L. (2023, February 23). Colour chemistry 2: photography and chromatography. Pressbooks.pub; RMIT Open Press. Retrieved from https://rmit.pressbooks.pub/colourtheory1/chapter/colour-chemistry-photography-and-chromatography/
- Digital photography vs. film photography. (2021, December 14). Asu.edu; ASU Online. Retrieved from https://asuonline.asu.edu/newsroom/online-learning-tips/digital-vs-film-photography/
- Processing Chemistry – Ophthalmic Photographers’ Society. (2022). Opsweb.org. Retrieved from https://www.opsweb.org/page/processingchemsitry
- John Straub’s lecture notes. (2024). Bu.edu. Retrieved from https://people.bu.edu/straub/courses/demomaster/photography.html
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