There is something magical in being able to display the passing of time with a single photo. There are many ways to capture the flow of time in a single image, being the use of a slow shutter speed the most straightforward one.
Slow Shutter Speed
Using a slow shutter speed can create strong, dynamic images of fast moving subjects like waterfall, torrents, clouds and city traffic. The range for the shutter speed may vary from only few seconds to a few tens of seconds, depending on the subject's speed.
Merging multiple exposures to create striking images
When you have to deal with relatively slow subjects, rather than take a single, very long, exposure, it pays off to take multiple photos and then combine them together in post production. It is like doing a time-lapse, only the final output is a single image rather than a movie. One of the most natural subjects for this kind of photography are star trails. Hundreds of frames are usually recorded so to cover hours of night sky and then all these frames are combined to get a single, striking image.
The motion of the milky way across the sky has been captured in the image below. Here I have combined ten exposures to cover 3 minutes of night time. The difference with shooting for trails is that, in this case, each exposure time was short enough to capture stars as point of lights, rather than as trails. This way, I still have a recognisable galaxy, motion blurred against the pin-sharp Obelisk.
Finally, inspired by the "Day to Night" work of photographer Stephen Wilkes, I'm starting to experiment with capturing the day/night transition in a single image. The image below is my first attempt to do so, and it required me to stay two hours in the busy location of Mont des Arts in Brussels, Belgium. This technique, for what I can see, is very challenging: first, you need to stay in a busy place with the camera mounted on a tripod for hours, which may be against local legislation (if police ask you to leave and you are unsure about your rights, I suggest you to pack you things and move), so try to get a decent composition without getting in the way of traffic and tourists. Next, is the challenge to get it right in-camera, meaning to properly deal with the ever changing light. Finally, you need to combine all your images: I suggest you to shoot quite often (I did it every 15 minutes or so) and to take multiple images every time a the time for a new sequence is up, so to be able to choose later between different scenes to compose your final image.
I think this last technique is best suitable for busy urban shots: see your city breath and live in front of you with the passing of the hours and put all this into a single image is simply amazing to me. Pure poetry.
I decided to go with a less ambitious project than Stephen's "Day to Night": I will limit myself to cover the period that goes from just before the golden hour to the blue hour, to make my "Golden to Blue" project. Stay tuned.