18 29 June 2019 I http://www.amateurphotographer.co.uk I subscribe 0330 333 1113
Technique EXPOSURE MASTERCLASS
HISTOGRAMS are important tools to help digital photographers
assess and interpret exposure. Most DSLRs allow photographers to
view a ‘live’ histogram in live view, while mirrorless cameras allow
you to preview the histogram through the EVF. You can also view
a photograph’s histogram when you replay an image.
Basically, a histogram is a two-dimensional graph that maps an
image’s tonal extent. The horizontal axis represents the tonal range
from pure black (0, far left) to pure white (255, far right), while the
vertical axis illustrates how many pixels have that particular value.
Despite what people say, there is no such thing as a perfect
histogram – it all depends on the subject matter.
Use your discretion
Generally speaking, you want the graph to show a good spread of
tones across the horizontal axis, without any sharp peaks on the far
left or right edge. If the graph shows the majority of pixels grouped
to the left, this normally indicates a dark, underexposed image; if the
graph is biased to the right, this likely indicates an overexposed image.
However, you do need to use a bit of discretion when reading
histograms. For example, if you are photographing a silhouetted
subject, you would fully expect to see a sharp spike on the far left of
the graph, while if you are shooting a misty or snowy scene (like the
one above), the histogram should be weighted toward the right edge.
However, when a histogram is falling off one side of the graph, it is
‘clipped’ – and once a pixel is recorded as either pure black or pure
white, no detail can be recovered and the image quality is affected.
By regularly checking histograms, you can easily assess exposure
and avoid costly mistakes. For example, if your histogram is pushed
up on the right edge (indicating overexposure), simply apply negative
exposure compensation (or select a faster shutter speed if you are
in Manual mode) in order to achieve better exposure.
If you are using the live histogram, it will adjust as you apply the
compensation, and you will be able to see when you’ve applied just
the right level to achieve correct exposure.
What is perfect
exposure?
In most instances, the correct
exposure is one that records
a scene or subject exactly as
our eyes see it. But it is worth
underlining that a technically
correct exposure will not
always produce the most
aesthetically pleasing or
creative result. Nothing in
the photography rulebook
says we always have to capture
things just as our eyes see
them. Understanding exposure
and how to manipulate it is a
key skill if you want to create
eye-catching pictures.
In truth, the correct exposure
is one that is faithful to your
vision and an interpretation
of the scene at the moment
you triggered the shutter.Which exposure
mode should you use?
Most consumer cameras have
a number of pre-programmed
modes optimised for diff erent
subjects, but they tend to limit
control so I would suggest you
ignore them in most situations.
Instead, it’s best to rely on theIf you’re shooting a misty or snowy
scene the histogram will be
weighted towards the right edge‘Core Four’: Programmed Auto
(P), Aperture Priority (A or Av),
Shutter Priority (S or Tv) or
Manual (M). Your choice of
exposure mode is important,
with each off ering a varying
level of control. The key thing
for most subjects is that you
control depth of fi eld – you
don’t want the camera guessing
the eff ect you’re after. For this
reason, I usually opt for either
Aperture Priority or Manual.
Aperture Priority is a
semi-automatic exposure
mode, meaning that once
you’ve selected the f/stop,
the camera will select what
it believes to be the correct
shutter speed to achieve good
exposure. Your Through The
Lens (TTL) metering is
typically very reliable and
should select the correct
corresponding shutter length.
If you opt for Manual
exposure mode instead, you
will need to set the shutter
speed yourself. This is not as
daunting as it sounds. As with
all other exposure modes, the
camera takes a light meter
reading from the scene orHow to read a histogram