What
happens when we select a certain ISO
value in our digital camera? What is the
best ISO setting for our particular camera?
Image
sensors have a so-called native sensitivity.
Native sensitivity cannot be changed, because it is
inherent to a certain sensor. Therefore, when we change
the ISO speed setting, something
must occur involving the circuitry serving the photosensitive
sensor.
ISO
setting > native sensitivity.
We must know that the electronic charge created inside
the photosensitive array of the image sensor is first
sensed and transformed into an analog voltage by an
amplifier and then an analog to digital converter
(ADC) transforms this voltage into a digital number.
output = gain * input
The
greater the output, the brighter the image. When the
photographer opts for an ISO speed greater than the
native sensitivity, the gain of this amplifier is
increased. For instance, if the selected ISO is twice
as much as the native sensitivity, the gain doubles.
As the signal is increased, leading to a brighter
image, the noise is increased as well, leading to
a noisier image. In some cases, a fiddling in RAW
data may also occur to boost to very high ISO speed.
ISO
setting < native sensitivity. For instance, if
the selected ISO is half the native sensitivity, brightness
values represented by each RGB channel are halved.
Conclusions
, drawbacks arise using an ISO setting both higher
and lower than the native sensitivity. So, it is best
to shoot at the sensor’s native ISO whenever
possible.
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