Flexing the powerful sensor of the dSLR Camera

Flexing the powerful sensor of the  dSLR Camera
With very few exceptions, digital SLR sensors are much bigger than their
point-and-shoot camera counterparts, and this size gives them a larger area
that can capture light and, potentially, great sensitivity to lower light levels.
(Some non-SLR cameras give up compactness to provide somewhat larger
sensors, but they’re still fairly rare.)

A dSLR’s extra sensitivity pays off when you want to
1. Take pictures in dim light.
2. Freeze action by using shorter exposure times.
3. Use smaller lens openings to increase the amount of subject matter
that’s in sharp focus.

Within the Canon digital camera
line alone, you find digital SLRs that
have 22.2mm-x-14.8mm to 24mm-x-
36mm sensors (the size of a 35mm
film frame). By comparison, some
of Canon’s digital point-and-shoot
cameras use a sensor that measures
only 7.8mm x 5.32mm. Put in terms
that make sense to human beings,
the dSLR sensors have 8 to 20 times
more area than their Lilliputian
point-and-shoot sensor-mates.

If you think of a sensor as a rectangular
bucket and the light falling on
it as a soft drizzle of rain, the large
buckets (or sensors) can collect more drops (or the particles of light called photons) more quickly than the small ones. Because a certain minimum
number of photons is required to register a picture, a large sensor can collect
the required amount more quickly, making it more sensitive than a smaller
sensor under the same conditions.
In photography, the sensitivity to light is measured by using a yardstick
called ISO (International Organization for Standardization). Most point-andshoot
digital cameras have a sensitivity range of about ISO 50 to ISO 100 (at
the low end), up to a maximum of ISO 800 to ISO 3200 (at the high end). Some
point-and-shoot models have even higher sensitivity settings, but it remains
to be seen how useful these ultra-high ISO non-SLR models are. Indeed, many
models that have high ISO settings generally don’t do a very good job in
terms of image quality.
In contrast, digital SLRs — which have more sensitive sensors and larger
light-gathering pixels — commonly have usable ISO settings of up to at least
ISO 1600. Many are capable of ISO 3200 or may range up to a lofty ISO 25600!
This extra speed does have a downside, as you can see in the following section.
But, in general, the added sensitivity allows people to shoot photos in dim
light, take action pictures, or stretch the amount of depth-of-field available.
Reducing noise in your photos
Visual noise (or just noise) is that grainy look that digital photos sometimes
get, usually noticeable as multi-colored speckles most visible in the dark or
shadow areas of an image. Although you can sometimes use noise as a creative
effect, it generally destroys detail in your image and might limit how
much you can enlarge a photo before the graininess becomes obtrusive.
The most common types of noise are produced at higher sensitivity settings.
Cameras achieve the loftier ISO numbers by amplifying the original electronic
signal, and any background noise present in the signal is multiplied along with
the image information.
Point-and-shoot digicams often don’t have ISO settings beyond ISO 1600
because the noise becomes excessive at higher ratings, sometimes even
worse than you see . However, you can
boost the information that the big dSLR sensors capture to high ISO settings
with relatively low overall noise. I’ve used digital SLRs that had less noise at
ISO 1600 than some poor-performing point-and-shoots displayed at ISO 400.
Obviously, the large sensors in dSLRs score a slam-dunk in the noise department
and make high ISO ratings feasible when you really, really need them.

Noise doesn’t always result simply from using high ISO settings: Long exposures
can cause another kind of noise. Although some techniques can reduce
the amount of noise present in a photo (as you can discover in Chapter 2), by
and large, digital SLR cameras are far superior to their non-SLR counterparts
when it comes to smooth, noise-free images.
Thanks to the disparity in size alone, all sensors of a particular resolution
are not created equal, and sensors that have fewer megapixels might actually
be superior to high-resolution pixel-grabbers. For example, most older
10-megapixel dSLRs produce superior results to some of the newest
12-megapixel non-SLR digicams. So, no matter how many megapixels a
point-and-shoot camera’s sensor can hoard, that sensor generally isn’t as big
as a dSLR’s. And when it comes to reducing noise, the size of the sensor is
one of the most important factors.


Article From : Digital SLR Cameras and Photography For Dummies 3rd Ed. (Book)