CLOUD MOVEMENT AND BLUR
What’s the correct shutter speed to blur slow-moving clouds?
The amount of blur in the sky here depends on the speed of the clouds as well as the length of the exposure. In windy conditions, fast-moving clouds may blur nicely after a minute or so, whereas 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 eight, 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.