Like a regular camera, a digital camera has a
lens and a shutter that lets in light. But the light
strikes an array of image sensors or photosensitive
cells instead of film. The sensor array is a chip
about 6-11 mm across. Each image sensor is a
charged-couple device (CCD) which converts light
into an electrical charge. The charge is stored as
analogue information then digitized by another bit
of technology called an analogue to digital
converter (ADC). Every receptor in the array of
thousands creates one pixel, and for each pixel a
certain amount of information is stored.
Some digicams use CMOS chips as image sensors.
CMOS stands for complementary metal oxide
semiconductor; this refers to the process by which
the sensor is made. The process is the same one used
to mass produce DRAM and microprocessors so CMOS
sensors are significantly cheaper and easier to make
than CCDs.
Other advantages of CMOS sensors are that they
consume less power and can have other circuits
included on the same chip. These additional on-chip
features can include analogue-to-digital conversion,
cameral controls, image compression and anti-jitter
stabilization.
However, these other circuits use space that
would normally be used for light sensing. This makes
the sensor array less sensitive to light, resulting
in lower image quality when shooting indoors or
other low light conditions. In the final tally, CMOS
cameras are smaller, lighter, cheaper and more
energy efficient, but be prepared to sacrifice some
image quality.
Resolution
The optical resolution of a digital camera is
determined by how many pixels it can capture
horizontally and vertically (ie. 640x480). This
depends on how many individual image sensors are
present in the array. When you do the multiplication
a camera with resolution of 1024x768 has 786,432
sensors and produces the same number of pixels. More
pixels mean better resolution and sharper images.
Most cameras offer megapixel resolution which
sounds like a Japanese movie monster, but it's
actually one million pixels or more. Lower end
models have 1.3 megapixels while high end models
have 3-4 megapixels or more. The more pixels that
your camera supports, the higher the resolution and
quality of photos that you can take.
To print good quality color photos at the
standard film sizes 4"x6" or
5"x7" you'll need a 1-2 megapixel camera.
If you plan on printing as big as 8"x10"
then you're going to need to capture more
information so look for 2-3 megapixels for higher
resolutions. Those of you with deeper pockets and a
need for high quality images can go the extra mile
and buy four megapixel models or greater.
Just like scanners, digicams have interpolated
resolution on top of optical resolution. To get
interpolated resolution the camera uses mathematical
algorithms to average the information from two true
pixels, creating a third pixel between them. Since
more pixels are mathematically generated the
interpolated resolution is higher than the original
optical resolution. However, true optical resolution
is a more reliable indicator of image quality.
Viewfinder
and Display
On a regular camera,
you look through an optical viewfinder to frame your
shot. Low-end digital cameras provide an optical
viewfinder while more expensive ones replace the
viewfinder with a LCD (Liquid Crystal Display). This
is the same technology found in flat panel displays
or digital watches. On a digital camera, an
integrated LCD screen can range in size from 1.8-3.0
inches measured across the diagonal. Many cameras
rely on the screen as the sole viewfinder.
Focus
Most consumer cameras are either fixed-focus or
autofocus which is suitable for the average user.
With a fixed-focus lens everything from about four
feet out to infinity is in focus. This is great for
pictures like landscapes, but you won't be able to
shoot up close. Autofocus will automatically bring
whatever is in the centre of the viewfinder into
focus. Some cameras let you point the centre of the
viewfinder at an object and depress the shutter
button half way to lock the focus on that object.
While holding the shutter half way down you can then
reframe the shot with the object anywhere you want.
Selecting
a digital camera is a lot like ordering pizza. In a
pizza there are a few basic elements like the crust,
sauce and cheese which you can't do without. The
tough part is choosing from a huge list of toppings.
Likewise, with a digital camera certain features
such as resolution, picture storage and viewfinder
are essential considerations. But depending on your
tastes you might want options like a zoom, flash and
self-timer, just to name a few.