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3.2 THE SHUTTER CONTROLS LIGHT AND MOTION | ||
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The shutter keeps light out of the camera except during an exposure, when it opens to let light strike the image sensor. The length of time the shutter is open affects both the exposure of the image and how motion is portrayed in it.
Slower shutter speeds let more light strike the image sensor making an image lighter. Faster shutter speeds let less strike it and make the image darker.
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| In these pictures, the shutter was left open longer for the image on the right than for the one on the left. It’s this longer exposure time that has made the image lighter. | |
| The Way It Was: Early Shutter
Designs The shutter, used to control the amount of time that light exposes the image sensor, has changed considerably over the years. The earliest cameras, using materials that might take minutes to be properly exposed, came with a lens cap that the photographer removed to begin the exposure and then replaced to end it. As film became more sensitive to light and exposure times became shorter, faster shutters were needed. One kind used a swinging plate while another design used a guillotine-like blade. As the blade moved past the lens opening, a hole in the blade allowed light to reach the film. |
In addition to controlling exposure (the amount of light that reaches the image sensor), the shutter speed is the most important control you have over how motion is captured in a photograph. Understanding shutter speeds is vital if you want to anticipate if a moving subject will appear in your image sharp or blurred. The longer the shutter is open, the more a moving subject will be blurred in the picture Also, the longer it’s open the more likely you are to cause blur by moving the camera slightly.
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| A fast shutter speed (left) opens and closes the shutter so quickly a moving subject doesn’t move very far during the exposure, a slow speed (right) can allow moving objects to move sufficiently to blur their image on the image sensor. | |
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Katie turned a little just as the shutter opened causing unwanted blur in the image. |
Although digital cameras can select any fraction of a second for an exposure, there are a series of settings that have traditionally been used when you set it yourself (which you can’t do on many digital cameras). These shutter speed settings are arranged in a sequence so that each setting lets in half as much light as the next slowest setting and twice as much as the next fastest. The traditional shutter speeds (listed from the fastest to the slowest speeds) include 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, and 1 second. Although speeds faster than 1 second are fractions of a second most cameras display them without the numerator. For example, 1/2 second is displayed as 2.
| How To: Selecting a Shutter Speed
Look in your camera manual for a section on shutter preferred or shutter priority mode, or shutter speeds. _____________________________________________________________________________________________ |