Photography Foundations: 3 Elements of Exposure
July 22, 2013
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Written by Foundations instructor Laura Mackin
All designers use photography in some capacity. With this in mind, Harrington's Foundations Program has been collaborating with the Digital Photography Program on videos that illustrate basic photo techniques. Our first video covers exposure controls: (vimeo.com/70501344)
Harrington College of Design Video on Camera Exposure from Harrington College of Design on Vimeo.
A photographic exposure is the process of allowing light into a camera & onto a sensor. The image sensor records the light as pixels, creating a digital image file. This process involves 3 elements:
— Shutter Speed
Each element can be controlled by the photographer to achieve different visual effects. Once you're familiar with the visual effects of exposure settings, you can prioritize a specific element to achieve a specific result.
ISO is a measure of electronic sensitivity. The higher the ISO, the more easily the camera sensor absorbs light.
Here is a typical ISO sequence:
<< less light << >> more light >>
50, 100, 200, 400, 800, 1600, 3200
A high ISO, like 1600, is useful for dark situations. But it also tends to produce an image with more noise. To avoid image noise, it is best to shoot at the lowest ISO possible, typically 100.
A mechanical camera shutter is essentially a metal flap that prevents light from reaching the sensor. The shutter opens for a determined period of time, exposing light to the sensor.
Shutter speeds are measured in seconds or fractions of seconds. A standard sequence of shutter speeds ranges from 1/1000th of a second to 1 second. With each stop setting, the exposure time either doubles or halves. For example, reducing the shutter speed from 1/15th of a second to 1/30th of a second cuts the exposure time in half, thereby halving light intensity.
When you're selecting a shutter speed, consider the element of movement. Long exposures allow more time to record movement within a single frame. So, slow shutter speeds blur movement. A fast shutter speed will freeze quick motion, but allows less light to reach the sensor.
Typically, a camera lens contains a mechanical iris that opens & closes to allow controlled amounts of light to enter the lens. This opening is called the aperture, and can be adjusted with f-stop settings.
Here is a standard sequence of aperture f/stops for a modern lens:
<< less light << >> more light >>
f/22, f/16, f/11, f/8, f/5.6, f/4, f/2.8, f/2, f/1.4
Notice how the light intensity increases as the f/number decreases. These units are based on a formula that consequently assigns the smallest number to the widest hole. So, an aperture setting of f/2 is wider than f/22. Wider holes allow more light to enter the lens.
Focus is a key consideration when selecting your f/stop setting. Depth of field is a term for the possible range of distances that can appear sharply focused in an image. A narrow aperture, like f/22, provides a broad depth of field, meaning that most of your image will be in focus. A wide aperture, like f/2, limits you to a shallow depth of field, meaning that only part of your image will be in focus; the rest will be blurred. A broad depth of field is not always the most desirable choice. When only part of your image is in focus, the blurred areas do not distract from the main subject.