The water becomes a blur against the static surroundings. Try this with running streams, waterfalls or waves on a beach. Fields of wheat are also a good subject – corn blowing in the wind will be blurred by an exposure time of a few seconds while the rest of the landscape remains sharp. Neutral Density filters can be used to increase exposure length.
Ardeer, © Carlo Ferroni 2009, Canon EOS 5D
To create a time-lapse movie you shoot still images at intervals of anything from a second or two to a day or two. These images are combined and played back at 24 to 30 frames per second. If you shoot a city landscape every minute from two hours before sunset to two hours after, then played back at 24 frames per second you have 10 seconds of movie showing night falling and the city lights appearing.
Some time-lapse sequences are taken over much longer periods and can show, for example, the construction of a building in a movie sequence lasting only a few minutes.
How is this done? Well, first you need the camera fixed to a solid support for the period of the shoot. This is not too difficult if your time window is only a few minutes, or even a few hours, though you do need to protect the camera against knocks or other movement. If you are shooting over a period of weeks or months, you need a vantage point that is both stable and secure, or a system that allows you to return with the camera and lock it into exactly the same position for each exposure.