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9
■ BRIDGING THE FILM/DIGITAL GAP
Shutters: Another Way to Control Light
Digital cameras need shutters to control light just like film cameras. Some digital cam-
eras use a shutter that is mechanical, not unlike the shutters used in a film camera.
The shutter—be it a leaf shutter or a focal plane shutter—controls the amount of light
that strikes the sensor. The faster the shutter, the less light is allowed past; the slower
the shutter, the more light. Remember from basic photography that varying the shutter
speed and changing the f-stop is how you get more control over the amount of light
hitting the film or sensor, and also how you can stop or blur action or control depth
of field.
Theoretically, digital cameras can use the sensor itself as a shutter. This requires
a special sensor in which the pixels themselves are told electronically when to turn on
and when to turn off. As you can imagine, using this electronic method can produce
much faster speeds than anything mechanical. Engineers for Olympus, for example,
have produced speeds of 1/18,000th of a second. Speeds like this are inherently imprac-
tical because they require so much light (and such a wide aperture). Also, using sensors
as shutters in this way has its trade-off: it lowers the effective resolution of the sensor
because the sensor must devote half of the possible photoreceptor cell locations to stor-
age, and thus those locations can’t generate image information.
From a practical point of view, the key things to keep in mind when looking at
the capabilities of a digital camera shutter are:
• Just like with a film camera, an important creative option can be using a digital
camera that provides some control over a range of shutter speeds—especially if
you are shooting action. Most prosumer and professional digital cameras come
with a shutter priority or manual mode. Rarely do consumer-level digital cam-
eras offer such options.
Note: Throughout the book you’ll see reference to digital cameras as consumer, profes-
sional, or prosumer. These distinctions are rough, and some digital camera models overlap
categories. Generally speaking, however, consumer digital cameras are tailored to users who
prefer mostly point-and-shoot capabilities. Prices range from $100 to $400. Prosumer digital
cameras offer more user control, a wider variety of features, and to a certain degree, higher
pixel counts. Prosumer digital cameras generally start at around $600 and go to about $2000.
Professional digital cameras combine user control and higher pixel count with speed of use
and responsiveness and durability. These cameras typically have interchangeable lenses,
although this feature is found in many prosumer models. Prices for professional digital cam-
eras start at about $2500, and the sky is the limit.
• At this time, most prosumer and professional digital cameras feature shutter
speeds in excess 1/1000th of a second, which is plenty fast for most shooting
situations.
• Although extremely slow shutter speeds are an option on most digital cameras,
keep in mind that shutter speeds slower than 1/15th of a second often introduce
electronic “noise,” which shows up as blotchy patterns in continuous-tone areas.
Some digital cameras offer noise reduction modes, with some trade-off in quality.
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