 Shutter speed
It is the length of time a shutter is open; the total exposure is proportional to the duration of light reaching the sensor. There are three factors that affect the shutter speed: the scene luminance, the ISO sensitivity and the aperture size.
You can trade off shutter speed and aperture by using units of stops. A stop up and down on each will halve or double the amount of light regulated by each. For any given total exposure, or exposure value, a fast shutter speed requires a larger aperture (smaller f-number). Similarly, a slow shutter speed, a longer length of time, can be compensated by a smaller aperture (larger f-number).
Shutter speed is measured in seconds.
The typical shutter speeds of most cameras
Fast
1/4000 1/3200 1/2500 1/2000 1/1600 1/1250 1/000 1/800 1/640 1/500 1/400 1/320 1/250 1/200 1/160 1/125 1/100
Medium
1/80 1/60 1/50 1/40 1/30 1/25 1/20 1/15 1/13 1/10 1/8 1/69 15 1/4
Slow
0.3" 0.4" 0.6" 0.8"
Very slow
1 1.3 1,6 2 2.5 3.2 4 5 6 8 10 13 15 20 25 30 |
In sunlight the typical shutter speed is between 1/100th and 1/125th of a second.
Shutter speed changes the way movement appears in the picture.
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Very short shutter speeds are used to freeze fast-moving subjects, for example at sporting events. |
Very long shutter speeds are used to intentionally blur a moving subject for artistic effect. |
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In low light conditions a slow shutter speed must be used. This extends the time until the shutter closes and provides more light to the sensor.
It is important to mention the old rule about focal length and shutter speed. When using a lens of a given focal length the minimum shutter speed to avoid motion blur is the equivalent to the focal length measured in 1/secs.
E.g. when using a 50mm lens the minimum shutter speed would be 1/50sec. When using a lens with Image Stabilizer or if the camera has an optical Image Stabilizer there is a gain of about 3 stops (2 stops in early IS technology). That means that at 50mm it is possible to have a shutter speed of 1/125sec. The following chart shows the interaction between focal length and minimum shutter speed to avoid camera shake, including the typical improvement of 3 stops with Image Stabilizer (hey, this information should be on the manual of any IS device!).
Remember that if you are using a sub frame camera you must calculate the crop factor. If the lens has a 100mm focal length, with the 1.6x crop factor it is equivalent to a 160mm, thus you should use a minimum speed of (1/160sec or 1/80 if the lens has Image Stabilizer).
The Bulb setting
For astro photography and other very long shutter speeds the "Bulb" setting allows the photographer to set for how long the shutter will be open. In some cases the shutter time may be of several hours. A tripod is mandatory in such cases. |
