CHAPTER 2 INSIDE DIGITAL VIDEO CAMERAS^19
A sophisticated zoom lens
system provides real,optical
zoomas strong as 10X. Some
cameras try to embellish that
withdigital zoom, but as
you’ll see in Chapter 5, optical
zoom is what really counts.Anactive autofocussystem bounces
infrared lightoff the subject and mea-
sures the time it takes to return to gauge
the distance from the camera to the sub-
ject. Small motors use the distance infor-
mation to adjust the lens so the subject is
in focus. See more in Chapter 3.Anexposure system, similar to those found in
still cameras, measures the lighting and adjusts the
lens’s diaphragm to the correct aperture opening.
In most consumer video cameras, varying the
length of time that the shutter is open is not used to
control exposure. But the numberof times during
each second that the shutter is opened to create a
framemay be varied to produce slow-motion and
fast-motion effects. The standard for commercial
television in the United States is 30 frames per
second (fps); for motion pictures, 24fps.Some cameras
provide an option
of recording to solid-
state flash memory,
similar to that used in
still cameras. And
others record the
video and sound
directly to a DVD or
a hard disk drive.