How Digital Cameras Cure the Shakes
Next to the precision accuracy of a camera’s focus and the native depth of field that is inherent and different in every lens and at every
f-stop, there is a third factor that heavily influences the sharpness of a photo: your hands.
A sharp image is the photographer’s holy, and elusive, grail. You can be focused down to the breadth of an eyelash. You can have depth
of field from shining sea to purple mountain majesties. But your hands, at their steadiest, still are wiggling one to five times a second,
undermining your careful focusing. Even on a tripod, a gust of wind or a truck rumbling by is enough to ruin a photo. The slightest tremble,
twitch, tic, or tremor makes a picture look as if it were taken during an earthquake. The light passing through the lens continues along a
straight line, but the imaging sensor shifts and dodges the incoming light as if they were playing dodge ball. Instead of creating neat little
points of color, the sensor records a
blur. The longer the shutter time and
the longer the focal length, the wider
the blur.
The rule of thumb has been that, to
avoid noticeable blurring, the shutter
speed must be faster than 1/focal
length. In 35mm terms, that means if
you’re using a normal lens of 50mm,
you’re going to get blurring with shutter
speeds that photographers commonly
resort to when they’re using available
light: 1/25 of a second, 1/30, 1/2,
1/60, or simply any shutter speed
slower than 1/100 of a second. Screw
on a telephoto lens, which exaggerates
any movement, and you must use even
faster shutters. Most digital cameras
multiply the telephoto tremble. The
average image sensor is smaller than
a frame of 35mm
film, but most
pictures recorded
to film and those
captured by
sensor wind up
being printed the
same size. But the
digital photo has
to be blown up
more to match the
size of a film-
based picture.
Any of the flaws
in a digital photo
end up being
bigger relative to
the same flaws in a film print. A photo taken by a handheld camera, shooting at 1/60 of a second, is likely to turn out like the left photo
on this page.
Camera makers have come up with several ways to stifle vibrations in both still cameras and camcorders. To be effective—which means
reducing vibration so much that the photographer can use a shutter speed two to three stops slower—a VR (vibration reduction) system must
counteract vertical vibration (pitch), side-to-side (yaw), and every direction in between. And it needs to make the correction within a few
thousandths of a second.(^124) PART 2 HOW DIGITAL CAMERAS CAPTURE IMAGES