How a Camera Works
By: Alastair Isaacs
Tags: Art, Creativity, Photography, Life, Education

The camera is the beating heart of photography. This is the device where the magic happens — where light is captured and imprisoned, by chemical or electrical means. If you want to master photography, the camera is the essential place to start.

A Rolleiflex 3.5 camera, from the 1950s. Photo by Ardi Evans on Unsplash

There are many different types of camera. All essentially capture light, but, since the invention of the first photographic devices more than 150 years ago, countless different techniques for doing so have been developed. Nowadays most cameras are digital, and most serious photographers will have either a DSLR camera or a mirrorless camera.

Here we’ll cover those two types of camera. But don’t give up if you have another type of camera, even if it’s just a phone camera. The basic principles of the camera hold for most modern devices, and all photographers can benefit from understanding them.

There are two main parts to all cameras — an optical part, that manipulates light, and a chemical or electrical part, that captures light. Today most cameras use electrical methods to capture light, with chemical means relegated to older analogue cameras. Here, then, we’ll focus on the electrical ways of recording light.

The Basics

The image below shows a DSLR camera, a common type of digital camera. In the last few years mirrorless cameras have also become widespread, but the basic method of operation is not that different.

A Canon EOS 600D DSLR. Though released in 2010, it shows all the major features of a DSLR camera. Image by 600d licensed under CC BY-SA 2.0.

To take a photograph, a photographer must point the camera at the scene or object they want to photograph, and then prepare or compose the image. This is done with a viewfinder. On mirrorless cameras this is simple — the image is projected onto an electrical sensor, which is then displayed on a LCD screen.

On DSLR cameras, the process is a bit more complicated. A mirror is positioned inside the camera body. In its normal position, the mirror reflects the incoming light through as small window. The photographer can see and compose the image through this window. When the photograph is captured, the mirror flicks up, and the light is able to reach the electrical sensor.

In most other ways the two types of camera work in the same way. At the front of the camera is a lens, an optical component that the photographer uses to manipulate and focus the image. Once he or she is happy with the image, they press the shutter release. This triggers the sensor to capture light, storing the resulting image in a digital memory card.

The Optical Part

Let’s start by considering the optical functions of a camera. Put simply, a camera must take light from its surroundings and focus it on a receptor. This is normally achieved by a series of optical components — lenses or mirrors — carefully placed in the path of incoming light.

Light rays always travel in straight lines. This, unless you are close to a black hole or massive star, is considered an unbreakable law of physics. But to capture a photograph, we must take light coming from big objects — perhaps a building, a landscape or even a planet — and shrink it down small enough to fit on a sensor measuring a few inches across. This means we need to find a way to bend a light ray.

Luckily, thanks to fundamental rules of optics, lenses can do this. When a ray of light enters certain materials — like glass or water — it slows down. As it slows down, it changes direction slightly. By carefully controlling the shape of the material, we can control how this change in direction happens.

Lensmakers can design lenses to manipulate light in various ways. Some lenses — like magnifying glasses, microscopes or telescopes, can make small objects appear much bigger. Other lenses can do the opposite, shrinking large things down. Specially designed lenses and mirrors can create other effects — a hall of mirrors in a fun fair is a good example of all the possibilities.

As well as the shape of the lens, the distance between the lens and the sensor also affects the resulting image. This means that a single lens can actually offer a range of different magnifications, though that range is ultimately limited by the shape of the lens.

The optical parts of cameras must also deal with focusing the image. An image that is perfectly in focus will appear sharp, with different objects clearly distinguished. But an out-of-focus image appears blurred, with the edges between objects unclear.

To focus an image, the lens must bring all the incoming light rays together at the same point. Whether this happens or not depends on the position of the lens, the sensor, and the photographed object. How this happens is quite mathematical, but suffice it to say that a photographer can control the focus by adjusting the distance between the lens and the sensor.

The optics behind cameras is a deep and fascinating topic, and it will take far more than a few paragraphs to fully introduce it. If you are interested in learning more, you can find a good introductory guide here and a much more advanced guide here.

The Electrical Part

Once the optical part of a camera has magnified or shrunk the image, focused it, and readied it for the camera’s sensor, the electrical part of the camera must take over to capture the light.

It’s worth noting, before we start, that this part of the camera was not always electrical. Indeed, for most of the history of photography, this part was done by chemical methods. The most popular technique was to use a camera film — a roll of light-sensitive material that darkens in response to light. This film would need to be extracted from the camera and developed chemically to obtain the photograph.

The advance of digital cameras changed this. Instead of light-sensitive chemicals, digital cameras use arrays of electrical sensors. These sensors consist of grids of millions of buckets, or pixels, that each individually count how much light they see.

The internal components of a camera. The sensor is visible close to the centre of the photograph. Photo by Dan-Cristian Pădureț on Unsplash

Two terms are used to discuss sensors — megapixels, and resolution. Megapixel refers to the number of pixels in the sensor. For example, a camera described has having 16 megapixels has 16 million pixels in its sensor. This alone is actually not that useful. What really matters is the size of the sensor, and the number of pixels per square inch it contains — also known as the resolution.

In general, larger sensors will produce better photographs, and are also more expensive. But resolution is also important, even on small sensors. When buying a camera you should pay attention to the resolution of the sensor — normally expressed in dpi (dots per inch). To produce good quality images, a dpi in the range of 240–300 is usually enough.

Sensors can also be measured by their performance in low light conditions. These can be challenging scenarios for cameras — with limited light photographic noise becomes much more important, and a noisy image is bad to look at. Ideally sensors should have as little noise in low light levels as possible.

The Physical Part

There’s one more part of a camera — the actual body of it. This is what holds the sensor and the lenses, and which also carries things like batteries, memory cards and screens. Camera bodies can vary widely between models and manufacturers.

In general, though, lenses and camera bodies are sold separately. This allows a photographer to switch lenses depending on his needs. As we saw earlier, the shape of the lens determines its properties. As a result, camera manufacturers have developed a wide variety of lenses to suit every possible need. Part of becoming a photographer is building up a collection of lenses that fit your interests.

Memory cards are an important feature on all digital cameras. Most current digital cameras will support SD cards. These days there are many, many different types of SD card, and the type you need depends heavily on the type of photography you expect to do. But be warned! Some cameras only accept a limited range of memory card, so check what you need before you buy.

What we’ve covered here is only the bare basics of cameras. The topic — from lenses to sensors to the battle between DSLRs and mirrorless cameras is deep and almost endless. Ultimately, though, the camera, vital as it is, is just a tool. The real work of photography comes from the photographer, and, at first anyway, building an understanding of the rules and techniques of photography will get you further than an expensive camera can.

Over the next few weeks I will be publishing a series of tutorials on the basics of photography. These will take you through the essentials of taking good photographs — from fundamental principles of light, to compositional rules that have passed down over centuries. Follow me, or subscribe to my newsletter, to stay updated.

You can find the first article in this series here.