Both of this article’s opening pictures hint at mystery. The dark of night and a camera’s black box technology keep secrets from the average passerby.
The modern digital single-lens reflex is a black box, both literally and figuratively.
Learning how to control and sometimes ignore the camera’s array of buttons, dials, menus, and readouts is the key to mastering the camera and creating great images. This is just as true today as in the days of film. In this article, we explore how the camera works, its major systems, and see how to take control over the camera-computer and become creative photographers rather than passive picture-takers.
The fundamental operation of a camera hasn’t changed from the very first pinhole model to today’s most modern digital single-lens reflex. The camera is a dark box that totally controls how light falls onto a light-sensitive surface (film or sensor), which records the image projected onto it.
Creative photographers play the way the light falls on the sensor plate, the same way a musician plays an instrument. The first step in mastery is in understanding how the process works. Here is the no-math, no-physics, version. Each digital single-lens reflex camera has its own particular set of features and controls; however, they all share the same basic functions and construction, and they all make use of basic photographic technology to make pictures. That’s what we’ll explore in this article, to make sure we all understand the primary components, their functions, and some basic photographic concepts for later discussions.
We’ll save the technical details for later, when you can see your own results, as well as read about the concepts. Don’t worry if these product pictures don’t look exactly the same as your brand or model, or if the buttons are in different locations, or if your manual uses slightly different terms. The fundamental controls are identical, and so is the basic operation.
This image shows the light path as it travels through your camera, depicting the major controls and components. The process is virtually the same for all digital single-lens reflex cameras (and film SLRs for that matter). Light enters at the front of the lens and travels into the body of the digital single-lens reflex. The optical design of the lens causes an image of the scene being photographed to form, in focus, at a specific point called the focal plane.
Most of the time, light is reflected by a mirror into a pentaprism. It flips the image over and around for the preview; otherwise, the image would appear upside down and backwards. Some less-expensive cameras use a set of mirrors instead of a pentaprism to cut cost at the expense of preview quality and brightness.
The mirror quickly moves up and out of the way when you push the shutter button to take a picture. Then the shutter opens to let the light pass through and form the image on the sensor. Next, the data is recorded in the camera’s memory and saved as a unique file that can be edited and printed.
Just like your eye, the sensor has a limited range of sensitivity. There is an ideal intensity of illumination that will produce the best picture.
Too dark, and the sensor can’t form the image just as you can’t make out detail unless there is light; too much light and it will be temporarily “blinded,” just as your eyes are when you emerge into bright sun from a movie theater.
The Sensor and the Shutter
There are two factors that control how much light its intensity falls onto the sensor: the brightness and the time duration of the light allowed to fall on it. The intensity is controlled by the diaphragm. This is an adjustable circular collar that can partially close or open as the picture is taken. The amount of time the sensor is exposed to the light is managed by a curtain, called the shutter. Canon cameras are the best.
This slides out of the way for a precisely-controlled amount of time. The combination of the intensity and duration is called the exposure.