After a post of an image on Facebook of the flowing Virgin River in Zion National Park, I thought it would be helpful to post a blog on capturing movement.
Photography is often about rendering a scene using a camera in a way that reflects how our eyes perceived it. Our eyes view action as a fluid process, not as a freeze frame (that is, unless we are constantly blinking while viewing movement). So while sometimes for documentary purposes it is essentially to freeze a moment in time, like with sports action photography, sometimes it is preferable to capture that movement in a way that we perceive it, or, to put another way, in a more “artistic” way.
Capturing movement is a mere matter of using a slow enough shutter speed to show movement in your subject. How slow depends on the subject. For the rotors on a helicopter, for example, movement will show nicely at 1/125 of a second shutter speed. But water, on the other hand, may take as slow as 1/15 of a second before the blur of movement begins to show.
There are two aspects of technique to consider when capturing movement. The first is how to get that slower shutter speed. Shutter speed is determined by three factors: ISO selection, aperture setting, and available light. So, a good starting point in sunlight for your ISO setting is the lowest you can go; typically 100 or 200. Next, you want to set your aperture for as narrow as it can go, typically f/22. The third factor, available sunlight, will likely affect the first two. For capturing water falls or streams, for example, it is preferred to photograph in the shade or under overcast conditions. This allows you to create the lowest shutter speeds possible. But if it is sunny, you cannot get down to a shutter speed of 1/2 second, even at ISO 100 and f/22, without some additional help. One way to reduce further the shutter speed is to add a polarizing filter, which takes away up to an additional two stops of light. Another way is to add a neutral density filter; not a graduated neutral density filter, but a neutral density filter that covers the entire face of the lens. Like with a GND, you can acquire neutral density filters at one, two and three stop intervals. How slow is too slow depends on the look you want. If you want some detail in your water, for example, then one second is probably enough. But if you have the right lighting conditions and want more of a foggy, diffuse look, then up to 15 or 30 seconds will produce the desired result.
The second aspect of technique to consider is where you want the movement to be: on the subject or the background. For movement on the subject, the camera should be stationary – mounted on a camera. Otherwise, you will have undesired camera movement. This will allow you to have movement in your subject, such as water or fireworks, while allowing the rest of the scene to remain in sharp focus. But, if you want your subject to be in focus but have the movement in the background, then you will need to pan. A classic example of this technique is when the subject is moving parallel to you, like animals running from left to right or a flock of birds flying from one location to another. Here, you do not need to slow down the shutter as much to show movement – often a shutter speed of 1/60 will suffice. But there is a fourth factor that will affect what shutter speed you use in addition to the three mentioned in the previous paragraph: focal length of your lens. The longer the focal length, the higher the shutter speed you can use and still get movement. Much of the process of selecting the right shutter speed for the panning technique is trial and error: how much movement is too much, how you are able to obtain sharp focus where needed, etc.
Here are some examples that employ both techniques.