58 Better Available Light Digital Photography
to a TV camera crew that is using a microwave dish to
transmit the video feed back to their base station.Chip size vs. Noise
In general, imaging chips come in three sizes: Full-frame chips
are those that closely, even exactly, match the 36 × 24 mm frame
size of 35 mm fi lm. Some digital SLRs use the APS-H sized
sensor, which measures 29 × 19 mm; others more commonly use
the APS-C sized sensor, which measures 22 × 15 mm. Other
cameras use the Four Thirds system developed by Olympus that
is now being used by other manufacturers, including Panasonic
and Leica, and is smaller than most other digital SLR sensors.
The size of this sensor is 18 × 13.5 mm, and it has an imaging
area of 17.3 × 13 mm.When it comes to image quality
and reduced noise, size does
matter. On the left is the full-
frame chip from the Canon EOS-
1Ds Mark II. Next is the imager
from the Canon EOS-1D Mark
III, and fi nally there’s the chip
from the EOS Rebel Xti. Images
courtesy of Canon USA.
This is the original Kodak Four
Thirds CCD sensor used in the
initial camera offerings from
Olympus. More-recent cameras
introduced by Olympus have used
a Panasonic NMOS sensor
mounted to a fl exible circuit
board. It looks a bit different, but
is the same four-thirds size. Photo
courtesy of Olympus America.
There are lots of debates about the advantages and disadvantages
of using large, full-size (24 × 36 mm) imaging chips in digital
SLRs, but the one obvious advantage of full-frame sensors is
the ability to combine high resolution with large pixel size.
Remember that each pixel on an imaging sensor transmits
an electronic signal only in proportion to the brightness it
receives. In effect, a pixel is acting as a tiny light meter. A
larger pixel has a greater surface area available for gathering
light. More light collected means that less amplifi cation is
needed for the output signal of each pixel, and less is better
because magnifying low-level signals increases noise. For