Sony DSLR-A100K - alpha; Digital Single Lens Reflex Camera Brochure & Specs page 20

Taking your best shot
CAMERA CONTROL
photography. In Monitor AF, the
camera is always "pre-focusing"
and doesn't lock until you press
the shutter halfway. Thanks to pre-
focusing, the camera is faster to
take the shot, improving your chances
of getting exactly the shot you want.
And Monitor AF works together with
Multi-Point AF to intelligently capture
your subject.
• Continuous AF is ideal when the
subject may be moving towards or
away from you. It's especially useful
for unpredictable subjects such as
sports, pets and little kids at play.
Not only is the camera always
"pre-focusing," but the camera also
continues to track your subject right
up until the moment of exposure.
Flexible Spot AF Single AF is ideal for subjects that stand still. (Sample photo for
illustration purposes.)
Enables you to move the focus spot
almost anywhere in the frame, useful
for tripod shooting.
Manual focus
Manual control when you need it.
Most Sony cameras also include manual
focus for five preset distances, enabling
you to take control. The DSC-H7, H9, and
the a100 Digital SLR go beyond this with
continuously variable manual focus.
Continuous AF is ideal for fast moving subjects, particularly ones
moving towards you. The focus keeps tracking until the moment
of exposure. (Note: Continuous AF uses center-point focusing only.)
(Sample photos for illustration purposes.)
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power
on
1/2
press
shutter
released
power
on
1/2
press
shutter
released
power
on
1/2
press Monitor AF pre-focuses the shot to speed your picture-taking
when you want to capture a "decisive moment." (Sample
shutter
released photos for illustration purposes.)
CAMERA CONTROL
Exposure
Maximum aperture, the smallest f stop at
which the lens can be used is an important
attribute of lens quality. Lenses that are
capable of a very wide maximum aperture
An essential part of photography, exposure
(f1.4, for example) are called "bright"
because they admit plenty of light and "fast"
determines the amount of incoming light
because they enable the photographer to
that reaches the image sensor. Cameras work at faster shutter speeds. These lenses
also tend to cost more.
control exposure by varying the lens opening
(aperture) and the amount of time given to
Shutter speed
taking the picture (shutter speed). One of
Cameras use a shutter to control the duration
the creative joys of photography is that
of exposure. This duration is called the shutter
speed, and is typically a fraction of a second.
there's no single combination of aperture
Shutter speed ranges are typically designed
and shutter speed that's uniquely correct. to double or halve the speed with each step.
That's why shutter speeds typically form a
series such as 1, 1/2, 1/4, 1/8, 1/15, 1/30,
Aperture
1/60, 1/120 and so on.
The word "aperture" refers to both a physical As with aperture, the choice of shutter speed
part of the camera, a circular window inside affects more than the simple amount of
the lens that opens and closes, as well as
incoming light. Fast shutter speeds tend
the number that describes the size of the to freeze motion. Slow shutter speeds
opening. The number is also called an "f tend to exaggerate motion, in the form of blur.
number." This represents the focal length
of the lens divided by the diameter of the
Exposure Value
aperture opening. For example, in a 50mm
lens, a 12.5mm opening would have a
number of f4. A 25mm opening would be
The basic unit of exposure is the Exposure
f2. The smaller the f number, the wider the Value (EV). An increase of +1 EV represents
aperture opening. a doubling of the incoming light, either by
doubling the time the shutter stays open or
Aperture openings are typically designed to opening up the aperture by one f stop.
increase in discrete steps, called "f stops."
As you open the aperture, each additional
Aperture + shutter = creativity
f stop doubles the amount of incoming light.
Thanks to the geometry of the lens, each f
stop has an f number that's the square root
Each f stop doubles or halves the amount of
of 2 times the previous f number. That's why light. Each step of shutter speed adjustment
f stops form the characteristic series of f1.4, does the same. In this way, you can choose
f2.0, f2.8, f4, f5.6, f8, f11, f16 and so on. from several aperture/shutter combinations
that result in the same total value of incoming
The choice of f stop affects more than simply light. The result is more than just proper
the amount of incoming light. Wide apertures technical exposure. It's creative freedom.
(low f numbers) result in limited depth of
For example, in portraits, a combination
focus. So the background tends to blur. of open aperture and fast shutter speed
Narrow apertures (high f numbers) tend will tend to blur the background, throwing
to keep the entire scene in focus.
more attention on your subject. In sports
photography, the same exposure value
might combine a stopped-down aperture
and a slow shutter speed to create a beautiful
motion blur.
ISO sensitivity
In film, a third method of managing exposure
is the choice of film "speed" or ISO sensitivity.
"Fast" film with a high ISO number is better
suited for shooting in low light, at some cost
in picture grain. In a similar way, digital
cameras offer ISO sensitivity settings. These
use electronic gain to increase the image
brightness at some cost in picture "noise."
Typically each doubling of ISO sensitivity
rating equals +1 EV. This enables advanced
photographers to optimize the image by
adjusting shutter, aperture and ISO all
at once!
Auto Exposure (AE)
Of course, Auto Exposure (AE) systems can
make all the exposure decisions for you.
Sophisticated light metering and processing
can measure the light levels from your subject
and choose appropriate exposure settings.
• Backlight and highlight. One obvious
difficulty in auto exposure is the case
where your subject is significantly
Continued on page 38.
Smaller Larger
Iris Iris
Same Exposure Value
Longer Shorter
Shutter Shutter
The camera's iris controls the size of the lens opening
or "aperture." A larger aperture (lower "f number") means
more light can reach the CCD. For a given Exposure
Value, a wider aperture means a faster shutter speed
(shorter exposure time).
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