56 DIGITAL CAMERA^ DECEMBER 2019 http://www.digitalcameraworld.com
CAMERA COLLEGEimage. Increasing the ISO will amplify the
noise as well as the signal, for instance.
Some cameras are better performers at
high sensitivities than others, and both the
size and the pixel density of the camera’s
imaging sensor can play a part. Essentially,
the smaller and higher resolution the sensor
is, the sooner the effects of noise become
apparent at high ISOs. A large sensor
combined with a low resolution tends to
give cleaner results at these sensitivities.
Take a current low-light champion: the
Sony Alpha 7S II. This full-frame camera
offers a paltry resolution of 12.2MP, but
a sensitivity range that expands from a
maximum ISO 102,400 to ISO 409,600.
The majority of cameras are capable of
delivering low-noise results up to ISO 800,
with an acceptable amount of noise fromISO 800 to 3,200. Things tend to get
progressively rougher beyond this, but
high-ISO noise reduction can help to temper
the increase in noise, in JPEGs at least.
Camera-based noise reduction can
be rather a blunt tool, softening both the
noise and the fine details. You get more
freedom to adjust the strength of the
effect to a greater degree in photo-editing
software, as well as selectively applying
it to different parts of an image.
Long exposures can dish up more digital
artifacts too, as the sensor heats up during
the exposure. This is made worse if you’re
shooting in a warm environment or you
have been recording video prior to shooting.
Long-exposure noise reduction can help
with this, but it doubles the length of time
it takes to save an image to the card.Where grain can add to
the mood of a picture,
noise can simply leave you
in an ugly mood, such is
ǣɎɀȸƏɎǝƺȸƏȸɎǣˡƬǣƏǼǼȒȒǸShooting long exposures
Reduce the type of noise created as the camera heats up
In-camera noise
reduction is applied
when the image is
processed, so normally
only affects JPEG images.
However, long-exposure
noise reduction affects both
JPEGs and raw files. The
reason for this is that the
camera has to physically
take two images before
combining the information.
Once the main image has
been captured, the shutter
is closed in order to capture
a ‘dark frame’ exposure that
lasts the same length as the
original one. The camerauses this information to
map where the thermal
noise is, then subtracts this
from the main image.
The chief drawback of this
type of noise reduction is
that it takes the same
amount of time to create
the second exposure and
process the image as it does
to take the first shot – which
may be minutes in extreme
cases – and your camera
may be unresponsive during
this time. The extra step
also reduces battery life
at the same time as it
knocks down noise...LOW LIGHT
Shooting at night usually
requires a high ISO (high
noise!) or a long exposure
(and risk of more noise).SENSOR
The longer the shutter is
held open and the sensor
is charged, the more the
heat builds up.SENSITIVITY
Low ISOs lead to much
longer exposures, raising
the camera’s internal
temperature.HOT SPOTS
The result? ‘Hot’ pixels
and thermal noise. Cue
long-exposure noise
reduction...