The Canon Magazine 49
LONG-E XPOSURE LANDSCAPES
ESSENTIAL SKILLS CLOUD MOVEMENT AND BLUR
STEP BY STEP CALCULATE A LONG EXPOSURE
Find out how long you should lock your shutter open with the help of an exposure calculator
01 TAKE A TEST SHOT
If you want to shoot with a long exposure
to blur clouds like this, then it can be
helpful to begin with a test shot using a
high ISO. We used aperture priority at f/16,
ISO6400, giving a shutter speed of
1.3 secs. We can use this as a base to
work out an equivalent long exposure.
02 USE A CALCULATOR
An app like PhotoPils is helpful for
calculating equivalent exposures. Here we
lower the ISO to 100, which increases the
shutter speed to 1 minute 23 seconds.
Then to increase the time even more we
factor in a 3-stop ND filter, resulting in an
exposure length of 11 minutes 6 seconds.03 TIME THE SHOT
Now we lock open the shutter with the
cable release to take the shot, using a
stopwatch to keep an eye on the time.
When shutter speeds last for tens of
minutes a few seconds here or there
will have minimal effect on the exposure,
so you don’t have to be exact.THE AMOUNT of
blur in the sky depends
on the speed of the
cloud as well as the
length of the exposure.
In windy conditions
fast-moving clouds
may blur nicely after
a minute. In calm
conditions like the
evening we shot on, it’s
only possible to achieve
motion blur by pushing
the shutter speed
beyond several
minutes. You can see
the difference here
between exposure
times of 8, 20, 75 and
780 seconds. In the
shorter exposure detail
is retained in the
clouds, while in the
longer exposure it’s
blurred to streaks. The
other factor to consider
in scenes like this is the
balance of light on the
building and the sky.
What’s the right shutter speed to blur slow-moving clouds at dusk?
8 SECS
75 SECS
20 SECS
780 SECS