How does a camera work? A beginner’s simple guide on how to use a camera

Everyday, 1.8 billion photographs are shared on the web, pausing life and turning moments into digital pixels of information. But how does a camera take something that we see and turn it into digital pixels? How are cameras able to freeze time?

Photography is actually just as much a science as it is an art — yet a large majority don’t realize what happens every time they push the camera’s button or open a smartphone camera app. So how does a camera work? Here’s what happens every time you press that button — and how to use a camera to take better pictures.

The Basics: Light and How The First Cameras Worked

Imagine you are standing in the middle of a room with no windows, doors or lights. What do you see? Well, nothing because there’s no light. Now imagine you pull out a flashlight and turn it on. The light from the flashlight moves in a straight line. When that beam of light hits an object, the light bounces off that item and into your eyes, allowing you to see whatever is inside the room.

All light behaves just like that flashlight — it travels in a straight line. But, light also bounces off of objects, which is what allows us to see and photograph objects. When light bounces off an object, it continues to travel in a straight line, but it bounces back at the same angle that it comes in at.

That means light rays are essentially bouncing everywhere in all kinds of different directions. The first camera was essentially a room with a small hole on one side wall. Light would pass through that hole, and since it’s reflected in straight lines, the image would be projected on the opposite wall, upside down. While devices like this existed long before true photography, it wasn’t until someone decided to place material that was sensitive to light at the back of that room that photography was born. When light hit the material, which through the course of photography’s history was made up of things from glass to paper, the chemicals reacted to light, etching an image in the surface.

How does a camera work? The Lens

Since that first camera did not capture very much light, it actually took eight hours to take a single photograph. The image was also quite blurry. So how are we able to take sharp images in milliseconds today? A camera lens.

While light bounces off of objects, it can also pass through objects — but, when it does, it can actually change direction. A camera lens takes all the light rays bouncing around and uses glass to redirect them to a single point, creating a sharp image.

When all of those light rays meet back together on a digital camera sensor or a piece of film, they create a sharp image. If the light doesn’t meet at the right point, the image will look blurry or out-of-focus. A lens’s focusing system moves the glass piece closer or farther from the sensor or film, allowing the photographer to adjust the lens so that the object is sharp.

Distance also plays a role in how camera lenses are able to zoom in. When the front piece of glass moves farther away from the camera sensor, objects become closer. Focal length is the measurement of the distance between where the light rays first hit the lens and where they reach the camera sensor. For example, on a lens with a 300mm focal length, the light takes 300 mm to be directed back into a sharp point on the camera sensor. A 300mm lens is considered a telephoto, or a lens that’s able to bring far objects close.

How does a camera work? Film and digital sensors

— Photo: Casey Cosley

A camera lens collects and focuses the light — but how is that information recorded? Historically, photographers were also chemists of sorts. Film is made up of light sensitive materials. When those materials are hit with light from the lens, they captured the shape of the objects and details like how much light is coming off of them. In the dark room, the film that was exposed to the light is again put in a series of chemical baths to eventually create the image.

So then how do digital cameras work? While the lenses, techniques and terms are the same, a digital camera’s sensor more closely resembles a solar panel than a strip of film. Each sensor is divided up into millions of red, green and blue pixels (i.e. megapixels). When light hits the pixel, the sensor converts it into energy and a computer built inside of the camera reads just how much energy is being produced.

Measuring how much energy each pixel has allows the sensor to determine what areas of the image are light and dark. And since each pixel has a color value, the camera’s computer is able to estimate the colors in the scene by looking at what other nearby pixels registered. Putting the information from all the pixels together, the computer is able to approximate the shapes and colors in the scene.

If each pixel is gathering light information, then camera sensors with more megapixels are able to capture more detail. That’s why manufacturers often advertise a camera’s megapixels. While that’s true to some extent, the size of the sensor is also important. Larger sensors will gather more light, making them better performers for low light scenes. Packing lots of megapixels into a small sensor actually makes the image quality worse, because those individual pixels are too small.

Putting it into practice: How to use a camera

All modern cameras use a lens and sensor (or film) to record an image. But why then, can two people take a photograph of the same scene and end up with very different results? A camera is a bit more than a lens and a sensor, and adjusting those extra elements changes the way the final image looks.

One way that images become unique is through composition. A camera’s lens is incapable of seeing everything — composition is simply a term that is used to describe what the photographer chooses to leave in, and what they chose to leave out. Adjusting composition is often as easy as moving around in a scene — think moving forward or backwards as well as side to side or even kneeling or standing on a chair. Small changes in the camera’s position can make a big impact on the photograph.

Lenses can also help alter a photograph’s composition. With zoom lenses, the glass is assembled in a way that allows the user to adjust how close or far away the item appears. On a compact camera, zoom is often done with a small toggle at the top of the camera, while DSLR and mirrorless lenses have a twist control around the lens. Zoom is an excellent tool for cropping out distracting objects.

Another important aspect of photography is exposure, or how light or dark the image is, and it relies on a number of different factors that, put together, determine how much light is recorded.

Digital cameras have a built-in meter that measures the amount of light in a scene. While on auto, the camera’s computer chooses the correct exposure. While auto mode is not perfect and doesn’t allow you to customize the final look of the photo, you can shoot a properly exposed image (most of the time) by selecting “auto” mode inside the camera’s menu or, on more advanced cameras, a mode dial at the top of the camera.

Newbie photographers can still adjust the exposure without learning manual modes through exposure compensation. This feature simply lightens and darkens the image. On advanced cameras, exposure compensation is often adjusted by pressing the button with a + and – sign on it and turning the dial near your right thumb. The feature isn’t exclusive to advanced cameras though — on an iPhone, you can tap the screen, then touch the sun icon that appears and drag your finger up and down.

Once you’ve chosen an exposure mode (likely auto for new photographers) and determined what to include in the composition, just press the button at the top right of the camera, right? Yes — and no.

Pressing the top button (the technical term is shutter release) all the way will take a photograph, but pressing it halfway will focus the shot. Looking through either the hole at the top of the screen (which is called a viewfinder) or at the camera’s LCD screen, press the shutter release halfway. Check and see that what you want to be in focus (the “subject”) is actually in focus, then push the shutter release all the way to take the photograph.

Using a digital camera, the photograph you just took will appear on the LCD screen. If it doesn’t pop up automatically, press the button with the play symbol to bring up the photos you shot — you can use the arrow keys to flip through them. Thanks to that digital technology, you can view your images and reshoot them if you don’t like the composition or need to adjust the exposure compensation

While technology allows you to take a photograph with the touch of a button, it wasn’t always that way. Cameras collect and record light using some pretty neat science and advanced technology. The time machine may be science fiction, but the camera can freeze memories to last forever.

Want to do more than just point and shoot? Own a DSLR yet you’re still stuck on auto mode? Learn how to use manual modes to take your photography to the next level.