Page 38 - Photo Review

INSIDER

Electronic shutters transferred from the sensor, which is also
There are two types of electronic shutters – rolling LQÁXHQFHG E\ WKH DYDLODEOH SURFHVVLQJ SRZHU
shutters and 'global' electronic shutters – plus A millisecond delay between when the pixels
a hybrid type that combines mechanical and are shut off at the top of the sensor and when
electronic operations. Both rolling and global they turn off at the bottom introduces distortion,
shutters are controlled by the sensor itself. producing a 'rolling shutter effect', which is
Their main advantages lie in the fact they have common in video recordings.
no moving parts, which means there's no wear Usually the rolling shutter process is fast
and tear through multiple actuations. enough to be unnoticeable in movie clips,
Without moving parts, these shutters are although it can be visible in rapid pans and with
immune to shutter shock and can also operate fast moving subjects like propellers. Rapid pans
silently. They can also achieve very fast shutter will make the recorded image appear to wobble
speeds, with 1/16,000 second relatively (hence the name 'jello effect'), causing images
common in current mirrorless cameras and to become skewed, as shown in the illustration
some going as high as 1/32,000 second. on this page.
This is at least twice as fast as the top speeds 7KLV LV PDJQLÀHG IRU IDVW PRYLQJ REMHFWV
This illustration shows a typical leaf shutter partially
RI WKH PHFKDQLFDO VKXWWHUV LQ ÁDJVKLS '6/5V like propeller blades and will often show
open. Note the curved blades that pull back to deliver
A rolling shutter activates one row of up in still photos. They can also suffer
light all over the frame.
photosites at a time across the width of the from severe banding when shooting under
frame. The exposure takes place between the ÁXRUHVFHQW OLJKWV
WLPH WKH ÀUVW URZ RI SKRWRVLWHV LV LOOXPLQDWHG DQG Hybrid shutters combine a mechanical and
Leaf shutters are similar to the iris diaphragm
when the last row of photosites is shut down. a sensor-based shutter. A rotary mechanical
blades that control the lens aperture. They open
In some cameras, this can take as long as shutter is placed in front of the sensor to
and close in a circular motion and are usually
VHFRQG DOWKRXJK LQ WKH ÁDJVKLS PLUURUOHVV obstruct light when the sensor would otherwise
contained within the lens. Structurally, they are
cameras from Olympus, Panasonic and Sony it be initiating or completing each exposure. If the
complex but they expose all of the sensor at the
is closer to 1/60 second. Either way, it's similar rotary shutter is faster than the sensor more of
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to the speed of a slow mechanical shutter, the sensor is exposed for capturing light.
speeds up to 1/500 second, compared with
even though the actual exposure time for each Adding a mechanical shutter to a digital
1/250 second for the best focal plane shutters.
row of photosites is as brief as 1/16,000 second. sensor adds potential for vibrations and noise.
Being more complex, leaf shutters are
Most of the delay is due to the readout With both rolling and hybrid shutters, the bit
more expensive to produce and less reliable in
time: the time taken for all of the data to be GHSWK RI UDZ ÀOHV FDQ EH UHGXFHG WR HQDEOH
operation than focal plane shutters. Their fastest
shutter speeds are limited due to a lag between
opening and closing the shutter. However, they
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are quieter than focal plane shutters and don't
distort moving objects.
At fast shutter speeds, leaf shutters can cause
vignetting, as the central part of the image can
get more light than the edges. And because each
lens requires its own shutter, the range of focal
lengths and maximum aperture options available
is a limited. For these reasons, they are seldom
used in modern digital cameras.
Both types of mechanical shutters have moving
parts, which over time can suffer from wear.
The shutters in more sophisticated cameras are
usually 'rated' for a number of cycles, with a typical
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between 200,000 and 300,000 cycles.
The shutters in mid-level DSLRs can be rated
for between 100,000 and 150,000 cycles,
while even without a published rating the
average entry-level DSLR's mechanical shutter
should be good for at least 50,000 cycles.
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camera's shutter has actuated is provided in
A rolling shutter scans across the image plane (usually downwards), 'initiating' and 'terminating' rows of photosites
the box on page 38. in rapid succession as the frame is fully exposed.

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