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23
The a100 image sensor has more than fifteen times
the image area of the typical 1/2.5-inch type sensor.
Full APS-size image sensor
Achieving the ultimate in picture quality
in the a100.
If you want professional-grade resolution,
sensitivity and freedom from noise, there’s
simply no substitute for a professional-size
image sensor. That’s why the Sony a100
Digital SLR incorporates a sensor with a live
image area almost the exactly the same size
as the APS-C film frame: 23.6 x 15.8 mm.
To appreciate the APS advantage, compare
the a100 with a typical 5.1 megapixel
camera using a 1/2.5-inch type sensor
(live image area 5.76 x 4.29 mm). The
a100 sensor has more than fifteen times
the area of this typical sensor. And even
though the a100 has twice as many pixels,
each a100 pixel has more than seven
times the area of the typical pixel!
The larger image sensor has dramatic
advantages:
• Higher resolution
• Higher sensitivity
• Lower image noise
• Greater exposure latitude
• More selective focus
Sony Super HAD
™
CCD
image sensor
Incredible resolution, sensitivity and
clarity from the industry leader in CCD
image sensors – Sony.
Sony is not only the industry leader in charge
coupled device (CCD) image sensors, we
supply more digital camera CCDs than all
other companies combined! This expertise,
unrivaled in the industry, is evident in our
proprietary Super HAD
™
CCDs.
Sony uses a Hole Accumulated Diode (HAD)
design to achieve not only high resolution
but also low noise and superb low-light
sensitivity. The CCD structure alternates
between small light-sensitive windows and
Sony image
sensor
features
22
Charge Coupled Device
(CCD) sensors
CCD stands for Charge Coupled Device.
It’s often compared to a bucket brigade.
When light enters the “bucket” of a pixel’s
image sensing area, the light generates
an electrical charge. After the exposure,
charges are passed along to other buckets,
and then to an amplifier that converts the
charges to a voltage. CCDs exhibit high
image quality, with a minimum of unwanted
image mottling or “noise.”
The challenge of resolution
Together with the lens, the image sensor is
primarily responsible for achieving high
resolution. The number of pixels in the image
sensor generally determines the maximum
number of pixels in the recorded image.
This encourages CCD manufacturers to
squeeze smaller and smaller pixels into
a given image sensor size. But smaller
pixels come at a cost: sensitivity and noise.
The challenge of sensitivity
and noise
Smaller pixels represent smaller “buckets”
in which to collect electric charge. Other
things being equal, smaller pixels have
less “sensitivity” to light: they require more
light to achieve a given picture quality. In
addition, other things being equal, smaller
pixels are more prone to mottling in the
picture, the random flecks and specks of
picture “noise.”
The importance of size
Small pixels give you resolution. Big pixels
give you high sensitivity and low noise. It’s
a classic engineering tradeoff. One obvious
way to overcome this is to increase the
overall size of the image sensor. While
rarely prominent on the spec sheet, image
sensor size is just as important as the
number of megapixels.
Sensors are classified by “type,” measured
in fractions of an inch. Other things being
equal, each pixel in a 2/3-inch image sensor
will be four times the size of a pixel in a
1/3-inch type image sensor for dramatic
improvements in sensitivity and noise.
Larger image sensors also help you control
depth of field to achieve “selective focus.”
This creative tool helps your subject stand
out by blurring the background. The
geometry of large image sensors makes
them inherently better suited to selective
focus than small sensors. You can choose
to open the iris to blur the background. Or
stop the iris down to keep the entire scene
tack-sharp.
The inch “types” date back to the outside
diameter of the pickup tubes of old broadcast
television cameras. This outside diameter
was always much larger than the inside
target size. This has created a paradox.
Nothing about a modern 2/3-inch type
integrated circuit image sensor actually
measures 2/3-inch!
The challenge of dust
The image sensors of digital SLRs face
one challenge that the sensors of lens-
integral cameras never see. When you
take off the lens of a D-SLR, you expose
the image sensor to environmental dust.
Image sensor pixels are microscopically
small, from two to six micrometers across.
In comparison, dust motes can be huge:
40 micrometers across. So when a single
dust mote alights on the image sensor, it
can obscure many, many pixels. And once
dust has landed on the image sensor, it is
surprisingly difficult to remove.
Accumulating
Bucket
Carrying
Bucket
Charge
Amplifier
Vertical
Register
Horizontal
Register
Signal
Output
LIGHT
KEY
Operating principle of an “interline transfer” CCD image sensor. Buckets of charge in the light-sensing area are transferred
into the vertical registers, from which they go to a horizontal register and the amplifier.
CAMERA SYSTEMSCAMERA SYSTEMS
TRANSFER
SECTION
SENSOR
ON-CHIP MICROLENS
TRANSFER
SECTION
Light
Effective
Ineffective Photo shielding AI
An engineering marvel, the Sony 10.2 Megapixel Super
HAD CCD.
The Sony microlenses maximize low-light performance by directing light onto the sensor areas and away from the
non-sensing transfer sections.
Previous microlens designs (left) miss some of the
incoming light. Our Super HAD design (right) gathers
more light for even higher sensitivity.
transfer sections that provide DC voltage
and output connections. To maximize
sensitivity, the Sony design uses an array
of microlenses on the CCD surface to
gather the light that might otherwise miss
the light-sensitive areas.
And Sony CCD technology continues to
advance. Sony refinements to the silicon
substrate enable succeeding generations
of Sony digital cameras to “have their cake
and eat it, too.” Each generation features
more megapixels, while maintaining or
improving sensitivity and noise performance.
Take the lens off a digital SLR and you’ll quickly realize
why anti-dust technology is so important.
Shooting the digital way
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