Taking advantage of exposure time
Professional photographer Jake Crosby explains the effects of exposure time on your photos and how to use it to your advantage.
Exposure time or shutter speed refers to how long the cameras shutter is open for, the amount of time the film or digital sensor is exposed to light coming in the lens. Exposure time is quoted in seconds eg 1/125 sec (a 125th of a second). Most digital cameras and a lot of film cameras give you control over the exposure time.
We can use this control to our advantage in several ways. Firstly, a longer exposure time allows more light to hit the cameras sensor and will therefore result in a lighter image, this can be used to brighten dark scenes. The opposite is also true - shorter exposure times darken bright scenes. Most of the time you will let your camera decide on the best exposture time for the scene you are shooting.
With this knowledge however, we can override the cameras default choice in some situations to create a more professional look. The most common reason is to freeze fast motion in action shots. A fast shutter speed will allow the camera to capture light from only an instant, freezing that instant.
A long exposure time will capture everything that has happened in the time the shutter was open. This technique is often used when photographing moving water, while the shutter is open all the turbulent movement of the water evens out and looks smooth. For this to work well you need the camera to be completely still, any movement will cause the positions of things in your photo to move within the frame, they will be recorded in all the positions they have moved through and look blurry. For this reason it's best to use a tripod.
As you now know, adjusting your shutter speed will affect the brightness of your image, this must be dealt with for you images to still look good when applying these effects. The easiest way, if your camera supports it, is to use exposure priority mode, usually an S or TV on the mode dial. This will tell your camera to use the exposure time you choose and adjust the aperture and other settings (to be discussed in future) to control the brightness and compensate for the higher or lower exposure time. This will not be able to compensate for very fast of slow shutter speeds, usually it's best to choose the highest or lowest speed you can while you pictures are not too bright or dark. With a digital camera you can shoot and check, but most cameras have a display to indicate when the settings are too bright or dark.
