Cameras, whether the newest digital wonder or the (becoming old quickly) film cameras, share a lot of basic ideas and functions. If you know one, you can find the same functions in the other. Understanding how your camera works is the first step toward controlling it to get the pictures you want. For the sake of simplicity, I’ll talk about film cameras. The concepts are the same in digital cameras, it’s just the way digital cameras achieve each of the elements of exposure that vary.
Cameras are all just light-tight boxes that control the amount of light that falls onto a piece of film or digital sensor. They’re nothing magical, just a box. This controlled amount of light is called the “exposure.”
To get a good picture, you need to control or balance four things about light:
1. How long the light falls on the sensor or film (SHUTTER/TIME).
2. How large the hole is that the light passes though (APERTURE).
3. How sensitive the film or digital sensor is to light (ISO /film speed).
4. How strong the light falling on your subject is (NATURAL (ambient) or STROBE/FLASH light).
The four parts of exposure all work together to get the intensity of light hitting the film or sensor to the right level. The first, time, is controlled by how fast the camera’s shutter opens and closes. The shutter is a set of thin metal plates in place between the film and the incoming light. It momentarily opens to admit light across the whole picture area and then closes. How long the shutter stays open is measured in fractions of a second (for example, 1/30th, 1/60th, 1/125th, 1/250th, 1/500th of a second). You’ll notice that the numbers are exactly or close to being double the previous number. As each increment of time gets longer, (a 30th of a second is longer than a 60th) the amount of light admitted doubles. To say it another way, the bigger the number on the bottom of the fraction, the shorter the duration of light exposure. 1/500th of a second is a lot shorter part of a second than 1/30th of a second. The important thing to keep in mind is that each increment either doubles or halves the amount of light, depending on which direction you go, down or up the scale. For example, each time you go from 1/30th to 1/60th, you halve the amount of light hitting the film because you have doubled the speed of the shutter opening and closing.
The second, aperture, (also called f-stop) is controlled by an adjustable set of flat metal plates arranged in a circular fashion in the lens base. This feature allows the amount of light to be controlled by the size of the hole created by the blades of the aperture. These numbers also create a doubling or halving of the amount of light admitted. The aperture numbers look like this: f2.8, f4, f5.6, f8, f16, f22. With aperture, the f2.8 is the largest opening and f22 is the smallest. There are larger aperture numbers and there are smaller numbers, but these are the most frequently seen sets. These numbers can usually be seen around the barrel of the lens near the base. The aperture settings are on a ring that can be adjusted to the required f-stop to control the amount of light you want on the film.
Now, so far, you have two controls over light: how large the opening is for the light and how long that opening is open for light to come through to the film/sensor.
The third, ISO setting (how sensitive the film or sensor is), is also usually set up in increments that double or halve. Common film speeds/ISO settings are: 25, 50, 100, 200, 400, 800, 1600, and 3200. The most sensitive to light is the 1600 and 3200 (fastest). They are used to take pictures in very low light conditions. ISO 25, 50, or 100 films or sensor settings (slower) would be used in bright conditions, generally speaking. A film being “slower” simply means it takes slightly longer to record an image with the same lighting conditions or needs slightly more intense light to record an image in the same time frame as a “faster” film to get similar results.
The fourth, the strength/intensity of the light, is important because if you don’t know how much light your dealing with, it’s hard to get the right settings on the camera.
This is where hand held light meters or in camera light meters measuring the light come into play. A hand held/separate light-metering device needs to be told (pre-set) to what the film speed/sensor ISO setting and the current shutter speed setting are, so it can give an accurate measurement of the lighting conditions. Armed with that knowledge, the light meter can tell you which aperture setting to use to get an accurate exposure for the film. I know that may sound complicated, but it’s not really all that bad. You tell the light meter the two settings that you already have or want to use, and it gives you the third. Many cameras have in-camera light meters and electronics that help simplify the whole process by being able to automatically know what the current ISO, aperture and shutter speeds are. Then they use a pointer or arrows in the viewfinder to guide you towards a correct exposure. Many point and shoot film cameras don’t use a light meter at all. They use a single film speed (usually 400 ISO) negative film (prints instead of slides) with a fixed “one size fits all” aperture and shutter speed. They rely on the store where you get your film developed to adjust the exposure after the fact to get an acceptable printed image from a not so perfect negative. Obviously, this has some advantages (simplicity) and some disadvantages (limited types of photos you can take).
Knowing what your camera’s light meter, shutter speed, and aperture are telling you, gives you more control over the way things will turn out. Knowledge is power! That’s called creative control. That creative control can give you more color in your sunsets (a smaller aperture can give you more saturated colors), make slow things look like their going fast (using a slow shutter speed lets things blur), or freeze the motion of very fast moving objects (a fast shutter speed helps freeze fast movement), to name just a few of the options. Understanding the basics of how your camera works helps you end up with the picture that you really wanted, instead of the “oh well, that’s good enough” picture that you might have ended up with.