What is Shutter Speed
The shutter speed is basically just the amount of time the shutter is open. In other words, it is the length of time that the image sensor can ‘see’ the scene you are capturing. The shutter speed is measured in seconds and the bigger the denominator the faster the speed, 1/1000 is faster than 1/250 for example.
Having a slower shutter speed can cause blur in your image due to camera shake, so the use of a tripod is recommended when slow speeds are used. The shutter speeds available will usually double with each setting, some speed you will probably see are 1/500, 1/250, 1/125, 1/60, 1/30 … ect. This doubling links to the aperture as well as increasing the shutter speed and decreasing the aperture value by one step will give you similar exposure levels.
There are cameras that allow you to open the shutter for seconds and not fractions of a second, some examples are 1, 10 and 30 seconds. Some even offer a feature called ‘BULB’ this is where the shutter will stay open until you release the trigger button. Speeds as slow as this are usually used for special effects or low light situations.
Freeze Frame or Capture Motion
When picking a shutter speed, you have to ask yourself is there anything moving in the scene, if yes you then need to decide on how you would like to capture this movement. If you choose that you want to freeze the motion, then you would want to pick a fast shutter speed, on the other hand if you choose that you want to intentionally blur the motion then you would want to pick a slower shutter speed.
The photo on the left was taken using a shutter speed of 1/320 seconds and you can see it produces a freeze frame. The photo on the right was taken with a shutter speed of 1.6 seconds which is a lot slower, this allows us to capture the motion of the water in this case.
Real World Situation
Changing the shutter speed while leaving the aperture and ISO alone is not really recommended, because as you change the shutter speed the other settings needs to be adjusted to counter act and compensate. For example, if you half the amount of light getting to the image sensor by change your shutter speed from 1/125 to 1/250, then you may need to increase the aperture from say f/16 to f/11. You could also change the ISO instead from ISO 100 to ISO 400.