Wikipedia states that, “Visual literacy is based on the idea that pictures can be read and meaning can be communicated through a process of reading”. The ability for an artist to weave a compelling story, they must make their audience feel what they feel. Whether it’s words, pictures or music, the artist must understand and manipulate the basic grammatical tools of their art form when speaking to that audience. For photographers, one such tool is exposure.
Exposure is the ability to capture the light from a scene and render that captured image on the light sensitive surface of the camera. Once this surface was film, and now it’s the camera’s imaging sensor. While the apparatus has changed, the technology has not. The three basic elements for controlling photographic exposure are still, ISO, shutter speed and lens aperture. Each of these elements control how light interacts with either the film or the camera’s sensor. They translate how bright or dark the final photograph will look. Let’s review how these elements work.
First, there is the ISO (International Organization for Standardization). The ISO defines the light sensitivity of the camera sensor or film. (For the rest of this article I will only refer to the camera’s sensor.) ISO is defined by high or low numbers that usually range from 100 up to 6400, but can start lower and end higher. Low numbers are not very sensitive to light. You would use a low ISO# in very bright scenes or if you are in a studio or are able to control the light source. If you are in a dark setting, you would use a high ISO# and visa versa. A low ISO# also will usually render fine detail in a scene. While a high ISO#, will be produce more image noise. This noise will interfere with the detail of the scene but will render more atmosphere from the scene. For general picture making an ISO of 400 to 640 will work well.
Next is the shutter speed. The camera shutter is the curtain that controls how long light will strike the sensor. A fast shutter speed allows the light to hit the senor for a shorter period of time. A slow shutter speed allows the light to strike the sensor for a longer amount of time. So if you are in a bright scene use a fast shutter speed. If in a dark setting use a slow shutter speed so light can hit the sensor for a longer period of time.
Then there is the lens aperture or f/stop. Apertures range from small to large, and control the intensity of the light that strikes the sensor. A large aperture opening allows a large amount of light to strike the sensor and a small aperture allows for a less light to hit the sensor. So, if you are in a bright scene you would use a small f/stop opening and if you are in a dark scene, you would use a large f/stop opening.
Shutter speed controls the timing or action that takes place in a scene of an image. The shutter controls how long the light will strike the sensor. Slow shutter speeds 1/30th of a second and slower (longer) allow the light to strike the sensor for a longer period of time. While faster shutter speeds, 1/100th of a second or shorter, allow the light to hit the sensor for a shorter period of time. In a dark scene you want to use a slow shutter speed , so more light can strike the sensor. In a bright scene, a faster shutter speed will let less light enter the camera.
Exposure also affect the mood and feeling of the photograph. When you want to stop the action happening is a scene, use a fast shutter speed. When you want to show an object in motion you use a slow shutter speed. Sports photographs have a tendency to use fast shutter speed. When you see a football player frozen in mid air catching a ball, that fast shutter speed is capturing a fraction of a second in time, like 1/1000th of a second. When you see a runner in the middle of the race and the background appears blurred the photographer is using a technique called panning. To pan, you use a slow shutter speed while tracking the motion of the runner. Because the shutter is open for a long period of time the moving background appears blurred. Since the camera is following the runner, they appear frozen.
Aperture opening controls the depth perception of the scene with a concept known as Depth of Field. Basically, depth of field controls the apparent sharpness of the scene both in front of and behind the main object in focus. Simply put, if you want the space behind the object you’re focusing on to appear out of focus, use a large f/stop opening. If you want everything to appear sharp in a scene use a small f/top opening. We call an out of focus background Shallow Depth of Field. This helps to isolate the main subject in the scene. When everything appears sharp in the scene, we call this Great Depth of Field.
At first these concepts may seem complicated. This is also why many new photographers get stuck in the habit of shooting photographs using Program or Auto modes of their cameras. However, to truly understand how to make great photographs you must understand how exposure works. And this takes practice. I recommend starting out using the Aperture Priority mode of your camera. In this mode you set the f/stop and the camera sets the shutter speed. Then try Shutter Priority where you set the shutter speed and the camera set the lens aperture for you. Finally, take off the training wheels and use Manual mode. Now you’re responsible for the whole shebang! If you would like practice the concepts of exposure, check out the SLR Camera Simulator.
Understanding exposure will allow you to eventually be able to pre-visualize your photographs before you push the shutter release. This will make you a better storyteller and your photographs more compelling no matter what the subject. Explore exposure by giving yourself a self assignment using these essential photographic grammatical tools. You'll be amazed by how they'll improve the storytelling power of your images.