Shutter Speed and the Sense of Movement
Shutter speed refers to the amount of time a camera's shutter opens and allows light to flow in onto the sensor. This, along with the right aperture and ISO choice will result in a properly exposed image. For more information on exposure, check out my post regarding the exposure triangle.
From an artistic perspective, shutter speed determines the sense of movement an image projects. For example, a very fast shutter speed, can help "freeze the moment" and capture a fast moving subject, such as this Formula 1 car, making it look stationary.
This photo was taken at a shutter speed of 1/5000th of a second in order to help freeze this car. You can freeze slower moving objects with lower shutter speeds, such as this Tel Aviv surfer I've photographed at 1/1250th of a second.
Sometimes, a blurry picture can help convey a sense of movement to the viewer. In order to achieve this effect we'll use slower shutter speeds. This image was taken at 1/160th of a second while using a technique called panning. Panning means moving the camera along with the subject and clicking the shutter release during the movement. This will create a blurry background and a relatively sharp subject which appears to be moving. For the speed the motorcycle was moving in relation to the stationary background, 1/160th of a second was slow enough to blur the background yet fast enough to keep the bike and rider in focus.
This is another example of panning I've taken of an electric bike in Tel Aviv. As the bike was moving much slower than the motorcycle, I took the image at 1/30th of a second in order to blur the background.
Shutter speed choice depends on the direction of the moving object - you can use a slower shutter speed and still freeze the object if it is moving towards you, while an object moving horizontally will require a faster shutter speed in order to freeze. Also, the wider the lends you use, the slower the shutter speeds you can use while still getting a sharp image. Images with telephoto lenses require much faster shutter speeds in order to maintain image sharpness. The third factor is the speed of your subject. For relatively stationary subjects, such as portraits, the rule of thumb is that the minimal shutter speed required in order to freeze a stationary object, while using a full frame camera, is 1 divided by the focal length. Multiply the focal length by about 1.6 in order to get the minimal speed necessary for a crop sensor camera. So if you're shooting a portrait with a 50mm lens on a full frame camera, the minimal shutter speed necessary to freeze the moment would be 1/50th of a second. On a crop sensor camera you would shoot at 1/ 80th of a second. This rule is very important if you want to capture sharp portraits. When photographing a moving object, you need to shoot with higher speeds in order to freeze the moment.
For other special subjects, you may want to use longer exposures. For example when shooting at night, in order to capture enough light to properly expose an image, you may need to shoot with longer shutter speeds. This picture of Big Ben was taken with a 20 second exposure. In order to avoid camera movement at such long exposure, I've used a tripod. Notice that Big Ben is well exposed after 20 seconds. A double-decker drove by during this exposure, yet it only took a few seconds to drive through which wasn't long enough for the camera to capture it, yet the camera did capture its bright lights, creating these light trails.
In order to create a sense of movement in slower moving subjects, such as stars, you can use extremely long exposures. In this photo of the stars, for instance, I've used an exposure of 1,919 seconds (just under 32 minutes!) in order to capture the stars' movement (AKA star trails).
As you can see shutter speed isn't only about exposure, but can really help you tell your story in various ways. Go out and experiment with it!
Keep up the good light!
Yehonathan