in stops with, again, the values
either doubling or halving with
a one-stop adjustment. So, for
example, ISO 400 is twice as
sensitive as ISO 200, and ISO 100
is half as sensitive as ISO 200.
However, again many cameras
allow for these adjustments to
be made in either one-third stop
or half stop increments for fi ner
control. You might select a higher
ISO setting, perhaps 800 or 1600,
when shooting sports action
because it will then allow you to
use faster shutter speeds with
smaller apertures than a slower
ISO setting (at a given exposure
value). However, as just noted, the
low sensitivity settings will deliver
optimum sharpness and detailing,
but in low-light situations, you will
then need to use very slow shutter
speeds and/or larger apertures to
obtain the correct exposure (and,
consequently, may have to put the
camera on a tripod).
The good news is that high-ISO
performance – even with smaller-
sized sensors (remember thatsensitivity is related to pixel size)- is now good enough to allow
shooting at ISO settings that were
never available with fi lm. If you’re
only making smallish prints (i.e.
no bigger than A4) or posting the
images online, there’s even more
scope for shooting at very high ISO
settings such as 12,800, 25,600 or
even 51,200. Some stratospheric
high ISO settings are now available
on higher-end D-SLRs and mirrorless
cameras, but the reality remains
that noise is still an issue so their
‘real world’ applications are limited.
Taking Control
What happens if you change,
say, the aperture, but then don’t
adjust the shutter speed to
compensate? If you’ve selected a
smaller aperture, then the image
will be underexposed. If you’ve
selected a larger aperture, the
image will be overexposed. The
same outcomes will happen if you
set either a slower shutter speed
without adjusting the aperture to
compensate. However, this isn’tof the microlenses which help
concentrate the light rays over
each photodiode.
Like a fi lm’s speed it is a
fi xed value – say ISO 200, for
example – but digital cameras
also allow for higher sensitivities
to be set. This is achieved via
electronically amplifying the signal
from the sensor, but this process
also amplifi es the interference
component which creates ‘noise’.
The continued refi nement of noise
reduction processing is delivering
ever better high ISO performance
from digital cameras, but there
are still some image quality issues
caused by the processing’s ‘side
effects’ (often called artefacts)
which essentially limit the
reproduction size when making
prints. One option is to shoot
RAW fi les – which aren’t corrected
in-camera like JPEGs – and then
perform the noise reduction
processing later using image-
editing software.
Like apertures and shutter
speeds, ISO settings are adjustedalways a bad thing because you
may, in fact, deliberately want to
either under- or overexpose an
image, either for technical reasons
or for creative effect. An image
where highlights – the lighter
tones – predominate is described
as being high-key, while one where
the shadows – or darker tones –
are dominant is called low-key.
Again, only by manually setting
the apertures and shutter speeds
do you have this level of control,
although there are alternative
options which will be covered in
the next article.
With experience, you’ll learn to
recognise when a lighting situation
or the type of scene demands
some intervention on your
behalf to achieve either a correct
exposure or a desired creative
outcome. Next we’ll look at how in-
camera light meters actually work- and so why you can’t always rely
on a camera’s automatic exposure
control system – and the ways
you can take charge to create the
images you really want.
BACK TO BASICS
74
The classic shutter speed dial has made a
welcome return to contemporary digital cameras
(this is on the Fujifi lm X-T2). The ‘halves/
doubles’ relationship between full-stop settings
again applies so, for example, 1/125 second
doubles the exposure from 1/250 second.The ‘halves/doubles’ relationship between full-
stop settings also applies to ISO – or sensitivity
settings – so, for example, ISO 400 is twice as
sensitive as ISO 200. On this particular dial,
one-third stop settings are also provided.The manual aperture
collar on the ZF.2 (Nikon)
mount model of the
Zeiss Otus 55mm f1.4
prime lens. However,
many interchangeable
lenses no longer have
this control and manual
aperture adjustments
are made from the
camera body. Full-stop
settings are marked here- from f1.4 to f16 – but
half-stop adjustments
are possible.
BACK TO BASICSBACK TO BASICSBACK TO BASICSBACK TO BASICSBACK TO BASICSBACK TO BASICSBACK TO BASICS
1 SHUTTER SPEEDS
2 ISO SETTINGS
3 APERTURE
SETTINGSCamMayJune17_072-074 BacktoBasics.indd 74 13/04/2017 12:16 AM