In most of the world, camcorders, or video
camera-recorders, have been a familiar sight for nearly 20
years. People take them everywhere: to school plays, sports
events, family reunions and even births! When you go to a
popular tourist spot, you are surrounded by them. Camcorders
have really taken hold in the United States, Japan and many
other countries around the world because they are an extremely
useful piece of technology that you can own for under $500.
Get Inside!
Want to know what a camcorder looks like when
you take it apart? Take
a look at a camcorder's many
pieces!
How can such a
small, relatively inexpensive device do so much? Particularly
for anyone born before the 1980s, it's simply amazing that
quality video cameras are now readily available as consumer
items, and that they're so easy to use. In this edition of HowStuffWorks,
we'll look inside these extremely popular devices to find out
what exactly is going on. We'll explore traditional analog
camcorders and also look at the technology used in digital
camcorders.
The Basics As the name suggests, a basic
analog camcorder has two main components:
A video camera
A VCR
The camera component's function is
to receive visual information and interpret it as an
electronic video signal. The VCR component is exactly like the
VCR connected to your television: It
receives an electronic video signal and records it on video
tape as magnetic patterns (see How VCRs Work
for details). A third component, the viewfinder,
receives the video image as well, so you can see what you're
shooting. Viewfinders are actually small, black-and-white or
color televisions, but many modern camcorders also have larger
full-color LCD
screens. There are many formats for analog camcorders, and
many extra features, but this is the basic design of most all
of them. The main variable is what kind of storage tape they
use.
Get Inside!
Want to know what a camcorder looks like when
you take it apart? Take
a look at a camcorder's many
pieces!
Digital camcorders
have all these same elements, but have an added component that
takes the analog information the camera gathers and translates
it to bytes of
data. Instead of storing the video signal as a continuous
track of magnetic patterns, it records the picture and sound
as 1s and 0s. Digital camcorders are so popular because you
can copy 1s and 0s very easily without losing any of the
information you've recorded. Analog information, on the other
hand, "fades" with each copy -- the copying process doesn't
reproduce the original signal exactly. Video information in
digital form can also be loaded onto computers,
where you can edit it, copy it, e-mail it
and manipulate
it.
In the next section, we'll look at the heart of the
camcorder, the semiconductor device that converts visual
information into an electronic signal.
That'll Never
Work...
The first
camcorder patent
was issued to the prolific American inventor Jerome
Lemelson in 1980. Lemelson, who passed away in 1997,
had tried to patent the idea for a camcorder in 1977,
but the U.S.
Patent Office rejected him, claiming the idea was
too far-fetched and that no company could ever be able
to manufacture and sell the device. Among other things,
Lemelson also invented crucial components for the VCR,
Walkman, ATM and
barcode
scanner.
The CCD Like a film
camera, a camcorder "sees" the world through lenses. In a
film camera, the lenses serve to focus the light from a
scene onto film treated with chemicals that have a controlled
reaction to light. In this way, camera film
records the scene in front of it: It picks up greater amounts
of light from brighter parts of the scene, and lower amounts
of light from darker parts of the scene. The lens in a
camcorder also serves to focus light, but instead of focusing
it onto film, it shines the light onto a small semiconductor
image sensor. This sensor, a charge-coupled device
(CCD), measures light with a half-inch (about 1 cm) panel of
300,000 to 500,000 tiny light-sensitive diodes
called photosites.
Each photosite measures the amount of light (photons) that
hit a particular point, and translates this information into
electrons (electrical charges): A brighter image is
represented by a higher electrical charge, and a darker image
is represented by a lower electrical charge. Just as an artist
sketches a scene by contrasting dark areas with light areas, a
CCD creates a video picture by recording light intensity.
During playback, this information directs the intensity of a
television's
electron beam as it passes over the screen.
Photons hitting a
photosite and creating electrons
Of course, measuring light intensity only gives us a
black-and-white image. To create a color image, a
camcorder has to detect not only the total light levels, but
also the levels of each color of light. Since you can produce
the full spectrum of colors by combining the three colors red,
green and blue, a camcorder actually only needs to measure the
levels of these three colors to be able to reproduce a
full-color picture.
How the three colors mix
to form many colors
In some high-end camcorders, a beam splitter
separates a signal into three different versions of the same
image -- one showing the level of red light, one showing the
level of green light and one showing the level of blue light.
Each of these images is captured by its own chip -- the chips
operate as described above, but each measures the intensity of
only one color of light. The camera then overlays these three
images and the intensities of the different primary colors
blend to produce a full-color image. A camcorder that uses
this method is often referred to as a three-chip camcorder.
How the original (left) image is split in a
beam splitter
This simple method produces a rich, high-resolution
picture. CCDs are expensive and eat lots of power, however, so
using three of them adds considerably to manufacturing costs
of a camcorder. Most camcorders get by with only one CCD by
fitting permanent color filters to individual photosites. A
certain percentage of photosites only measure levels of red
light, another percentage measures only green light and the
rest measure only blue light. The color designations are
spread out in a sort of grid (the Bayer filter below is a
common configuration), so that the video camera computer can
get a sense of the color levels in all parts of the screen.
This method requires the computer to interpolate the
true color of light arriving at each photosite by analyzing
the information received by the other photosites in the
vicinity. For a full explanation of this process, check out this
page.
If you've read How
Digital Cameras Work, then all this has probably been
familiar to you -- camcorders and digital still cameras both
take pictures using CCDs. But since camcorders produce moving
images, their CCDs have some additional pieces you won't find
in digital camera CCDs. To create a video signal, a camcorder
CCD must take many pictures every second, which the camera
then combines to give the impression of movement.
If you've read How Television
Works, you know that a television "paints" images in
horizontal lines across a screen, starting at the top and
working down. TVs actually paint every other line in one pass
(this is called a field) and then paint the alternate lines in
the next pass. To create a video signal, a camcorder captures
a frame of video from the CCD and records it as the two
fields. The CCD actually has another sensor layer behind the
image sensor. For every field of video, the CCD transfers all
the photosite charges to this second layer, which then
transmits the electric charges at each photosite, one by one.
In an analog camcorder, this signal goes to the VCR, which
records the electric charges (along with color information) as
a magnetic pattern on videotape. While the second layer is
transmitting the video signal, the first layer has refreshed
itself and is capturing another image.
A digital camcorder works in basically the same way, except
that at this last stage an analog-to-digital converter
samples the analog signal and turns the information into bytes
of data (1s and 0s). The camcorder records these bytes on a
storage medium, which could be, among other things, a tape, a
hard
disk or a DVD. Most of
the digital camcorders on the market today actually use tapes
(because they are less expensive), so they have a VCR
component much like an analog camcorder's VCR. Instead of
recording analog magnetic patterns, however, the tape head
records binary code. Interlaced digital camcorders
record each frame as two fields, just as analog camcorders do.
Progressive digital camcorders record video as an
entire still frame, which they then break up into two fields
when you output the video as an analog signal. (To learn more
about analog-to-digital picture conversion, check out this
page from How
Digital Cameras Work and this
article about analog and digital recording.)
The Lens As mentioned above, the first step
in recording a video image is to focus light onto the CCD,
using a lens. To get a camera to record a clear picture of an
object in front of it, you need to be able to adjust the focus
of the lens -- that is, move the lens so it aims the light
beams coming from that object precisely on the CCD. So, just
like film cameras, camcorders let you move your lens in and
out to focus light. Of course, most people need to move around
with their camcorders, shooting many different things at
different distances, and constantly refocusing is extremely
difficult.
This is why all camcorders come with an autofocus
device, usually an infrared beam that bounces off objects in
the center of the frame and comes back to a sensor on the
camcorder. To find the distance to the object, the processor
calculates how long it took the beam to bounce and return,
multiplies this time by the speed of
light, and divides the product by two (because it traveled
the distance twice -- to the object and back again). The
camcorder has a small motor that
moves the lens, focusing it on objects at this distance. This
works pretty well most of the time, but sometimes you have to
override it -- you may want to focus on something in the side
of the frame, for example, but the autofocus will pick up
what's right in front of the camcorder. To learn more about
autofocus mechanisms, check out How
Autofocus Cameras Work.
Camcorders are also equipped with a zoom lens. In any sort
of camera, you can magnify a scene by increasing the focal
length of the lens (the distance between the lens and the
film or CCD). An optical zoom lens is a single lens
unit that lets you change this focal length, so you can move
from one magnification to a closer magnification. A zoom
range tells you the maximum and minimum magnification. To
make the zoom function easier to use, most camcorders have an
attached motor that adjusts the zoom lens in response to a
simple toggle control on the grip. One advantage of this is
that you can operate the zoom easily, without using your free
hand. The other advantage is that the motor adjusts the lens
at a steady speed, making zooms more fluid. The disadvantage
of using the grip control is that the motor drains battery
power.
Some camcorders also have something called a digital
zoom. This doesn't involve the camera's lenses at all; it
simply zooms in on part of the total picture captured by the
CCD, magnifying the pixels. Digital zooms stabilize magnified
pictures a little better than optical zooms, but you sacrifice
resolution quality because you end up using only a portion of
the available photosites on the CCD. The loss of resolution
makes the image fuzzy.
One of the great things about a camcorder is that it can
adjust automatically for different levels of light. It's very
obvious to the CCD when an image is over- or under-exposed
because there isn't much variation in the charges collected on
each photosite. The camcorder monitors the photosite charges
and adjusts the camera's iris to let more or less light
through the lenses. The camcorder computer always works to
maintain a good contrast between dark and light, so that
images don't appear too dark or too washed out.
Formats
Analog Formats Analog
camcorders record video and audio signals as an analog track
on video tape. This means that every time you make a copy of a
tape, it loses some image and audio quality. Analog formats
lack a number of the impressive features you'll find in
digital camcorders. The main difference between the available
analog formats is what kind of video tape the camcorder
uses and the resolution. Analog formats include:
Standard VHS: Standard VHS cameras use the
same type of video tapes as a regular VCR. One obvious
advantage of this is that after you've recorded something,
you can pop the tape out and play it on most VCRs. Because
of their widespread use, VHS tapes are a lot less expensive
than the tapes used in other formats. Another advantage is
that they give you a longer recording time than the tapes
used in other formats. The chief disadvantage of standard
VHS format is that the size of the tapes necessitates a
larger, more cumbersome camcorder design. They have a
resolution of about 230 to 250 horizontal lines, which is
the low end of what's now available.
VHS-C: VHS-C camcorders record on standard VHS
tape that is housed in a more compact cassette. You can play
VHS-C cassettes in a standard VCR, but you need an adaptor
device that runs the tape through a full-size cassette.
Basically, though, VHS-C format offers the same
compatibility as standard VHS format. The smaller tape size
allows for more compact designs, making VHS-C camcorders
more portable. But the reduced tape size also means VHS-C
tapes have a shorter running time than standard VHS cameras.
In short play mode, the tapes can hold 30 to 45 minutes of
video. They can hold 60 to 90 minutes of material if you
record in extended play mode, but this sacrifices image and
sound quality considerably.
Super VHS: Super VHS camcorders are about the
same size as standard VHS cameras, because they use the same
size tapes. The only difference between the two formats is
that super VHS tape records an image with 380 to 400
horizontal lines, a much higher resolution image than
standard VHS tape. You cannot play super VHS tapes on a
standard VCR, but, as with all formats, the camcorder itself
is a VCR and can be hooked up directly to your television or
to your VCR to dub standard VHS copies.
Super VHS-C: Basically, super VHS-C is to
super VHS as VHS-C is to standard VHS: It's just a more
compact version that uses a smaller size cassette.
8 mm: These camcorders use small 8-millimeter
tapes (about the size of an audio cassette). The chief
advantage of this format is manufacturers can produce more
compact camcorders, sometimes small enough to fit in a coat
pocket. The format offers about the same resolution as
standard VHS, with slightly better sound quality. Like
standard VHS tapes, 8 mm tapes hold about two hours of
footage, but they are more expensive. To watch 8 mm tapes on
your television, you have to attach your camcorder and use
it as a VCR.
Hi-8: Hi-8 camcorders are very similar to 8 mm
camcorders, but they have a much higher resolution (about
400 lines). Hi-8 tapes are more expensive than ordinary 8 mm
tapes.
Digital Formats Digital
camcorders differ from analog camcorders in a few very
important ways. They record information digitally, as bytes, which
means that image can be reproduced without losing any image or
audio quality. Digital video can also be downloaded to a
computer, where you can edit it or post it on the Web. Another
distinction is that digital video has a much better resolution
than analog video, typically 500 lines. There are two consumer
digital formats in widespread use:
MiniDV: MiniDV camcorders record on compact
cassettes, which are fairly expensive and hold about 60 to
90 minutes of footage. The video has an impressive 500 lines
of resolution, however, and can be easily transferred to a
personal computer. DV camcorders can be extremely
lightweight and compact -- many are about the size of a
paperback novel. Another interesting feature is the ability
to capture still pictures, just as a digital camera does.
Sony has recently introduced MICROMV, a format that works
the same basic way as MiniDV but records on much smaller
tapes.
Digital 8: Digital-8 camcorders (produced by
Sony exclusively) are very similar to regular DV camcorders,
but they use standard Hi-8-mm tapes, which are less
expensive. These tapes hold up to 60 minutes of footage,
which can be copied without any loss in quality. Just as
with DV camcorders, you can connect Digital-8 camcorders to
your computer to download your movies for editing or
Internet use. Digital-8 cameras are generally a bit larger
than DV camcorders -- about the size of standard 8-mm
models.
DVD: DVD camcorders are still relatively rare,
as compared to MiniDV models, but their numbers are growing
steadily. Instead of recording magnetic signals on tape,
these camcorders burn
video information directly onto small discs. The main
advantage of this format is that each recording session is
recorded as an individual track, just like the individual
song tracks on a CD. Instead
of rewinding and fast-fowarding through tape, you can jump
immediately to each section of video. Other than that, DVD
camcorders are pretty close to MiniDV models in performance.
The picture is a little better on DVD models, however, and
DVDs can store more footage. Depending on the camcorder's
settings, a disc can hold 30 minutes to two hours of video.
The newer DVD camcorders support two DVD formats: DVD-R
and DVD-RAM. Both are three-quarters the size of DVD movie
discs and are encased in plastic cartridges (at least
while in the camcorder). The advantage of DVD-R
camcorder discs is that they work in most set-top DVD players.
The drawback is you can only record to each disc once, which
means you need to buy new discs regularly. You can record
over DVD-RAM discs again and again, but you can't
play them in ordinary DVD players. Like MiniDV tapes, you
have to either use your camcorder as a player for your TV or
copy your movie to another format.
These days, you can get a digital camcorder for $600 and
pick up some tapes for under $10. Digital
video editing programs simplify the editing process to the
point where you can master it in an afternoon.
Even low-end analog camcorders have so many helpful
features that anybody can get decent footage with a little
practice, and you can create quality movies with more in-depth
studying. The technology that was once the exclusive domain of
television professionals is now available as hobby equipment.
Whether you simply want to record birthday parties and
recitals or you hope to produce ambitious video projects, the
newest camcorders certainly have a lot to offer.
For more information on camcorders and related topics,
check out the links on the next page.
