Shutter Speed

Shutter Speed

Shutter speed is how long the shutter stays open to let light enter the camera to create the exposure for the photographic image. The exposure is determined by three factors: the shutter speed, the aperture of the lens, and the ISO film speed.

Shutter speed is measured in fractions of seconds, whole seconds, and minutes. The fraction ill 25 second is spoken of as “one, one twenty fifth” or “one twenty fifth of a second” or simply “one twenty fifth.”

1/125 second is often used for snapshots taken outdoors under sunny skies. Common, daytime shutter speeds are 1/125 and 1/60. Above and below these numbers are the so-called “fast” or “slow” shutter speeds. A fast shutter speed is commonly considered to be 1/250 second, 1/500 second, etc. A slow shutter speed would be 1/30, 1/20, 1 second, etc.

1/20 second is slow enough to blur a waterfall. 1/250 second will stop the action of many moving subjects. The photographer’s choice of exposure time can decide how the movement of the subject will be depicted in the final image: sharp or blurry.

Sometimes it is the photographer who is moving. A faster shutter speed is required for sharp images if the camera is used on a moving ship, boat, car, bus, train, bicycle, etc. Even images taken while sitting inside or learning against a car with the motor running will show the effects of the motor’s vibrations.

 Besides the obvious factor of the movement of the subject or photographer, there is another reason to choose a specific shutter speed: the shutter speed changes in conjunction with aperture to produce the same exposure. The same amount of light needs to enter the camera whether the shutter speed is fast or slow. If the shutter speed is increased or decreased, the size of the opening, the aperture, will open up or close down accordingly. In other words, a fast shutter speed uses a different aperture than a slow one (for the same exposure).

The ISO setting determines how the film or digital sensor soaks up the light and creates the image. In bright light situations a lower ISO is often sufficient for a good exposure at the desired shutter speed, because the film/sensor does not need to be as sensitive to light as in dark situations. For each ISO there is a different set of combinations of shutter speed and aperture.

There is more than one combination of shutter speed/aperture/ISO settings that can result in the same exposure. When the shutter speed is set first (at a specific ISO), there is a corresponding aperture chosen by the camera. The photographer can experiment with settings to affect the look of the subject matter. The subject’s action can be blurred or stopped. The background can be put out of focus or kept sharp.