How Does a Camera Capture an Image?

By Shawn McClain

Cameras take advantage of the properties of light to record an image.
i Jupiterimages/ Images

Cameras have become an integral part of everyday life, growing so popular that just about everyone carries one around around their neck and in their pocket or purse. But for something that has become so ingrained in our lives, not many people understand just how a camera captures an image. The technology behind the camera is based on the properties of light and the process of manipulating that process.

Capturing Light

Understanding how a camera captures an image first requires a basic understanding of light and how it works. The objects you see are interacting with individual particles of light, called photons. These photons reflect off of objects, changing their frequency slightly to correspond with the color of the object, and then they travel out where they can be observed. If you allow these photons to pass through a small opening, they will create an image of what's in front of the opening located just behind the opening. Capturing an image with a camera is all about manipulating this process.

The Lens

The lens sits in front of the opening, called an aperture, and focuses the incoming light photons to create a clear image a certain distance behind the aperture. By slightly adjusting the position of the lens you can alter which areas of the image are brought into focus and which are left out of focus. You can use different lenses for more specific tasks, such as capturing wide-angle shots or zooming into far-away locations, but the main point behind the lens is just to focus the image, and it's the lens that allows a camera to be compact.

The Action

When you press the button to capture an image with your camera, the shutter moves out of the way, allowing light in to strike your film or sensor, depending on the type of camera that you have. Along with the lens, the size of the opening that the light passes through, called the aperture, and the amount of time that the shutter remains open, called the shutter speed, will generally determine how the image appears. More advanced cameras have a host of additional settings, but those three aspects of the camera make up its basic functionality.

Capturing the Image

The way the image is recorded will depend on whether you have a digital camera or a film camera. In a film camera, the photons of light pass through the film, causing a reaction where they strike. The development process translates that reaction into brightness when creating the final picture. Color film uses several layers of film to record brightness levels for blue, green and red, which then translates into a full-color image.

A digital camera's sensor works similarly. Individual pixels, called photosites, capture photons as they enter, build up an electrical charge based on how many photons they capture. This information, which is again broken down into the three primary colors, is then translated into the image that you see on the screen.