Shutter speed refers to how long the shutter is open, and therefore how long the exposure is in your image. What do photographers mean when they refer to one stop or two stops? Read on to find out what you need to know.
Even a camera for beginners will probably offer control over shutter speed, and it's one of the key ways in which you determine how our images end up looking – check out our exposure triangle guide for more on that!
What is shutter speed?
What is shutter speed? Shutter speed forms one part of the exposure triangle, the other two parts being aperture and ISO. Whereas aperture controls how large the opening inside the lens is for light to pass through, and ISO how much light is required in order to create the image, shutter speed dictates how long the camera's sensor is exposed to light. The right balance of the three is what every photographer needs to consider if they're to achieve the image they expect.
The easiest way to control shutter speed precisely is to turn the camera's mode dial or mode setting (assuming it has one) to the Shutter Priority setting. Depending on which camera you use, this will be marked Tv (which stands for Time Value) or simply S. Once in this mode, you simply turn a command dial on your camera and you should see a figure in the viewfinder and/or the LCD screen jump between values like 1/125, 1/250, 1/500 and so on – and this is your shutter speed.
1/125 is 1/125sec, which means that the shutter inside your camera will be open for one-hundred-and-twenty-fifth of a second. This may be a physical shutter or an electronic one, but the principle is the same and your camera's sensor is exposed to light for this period of time.
If you then change the shutter speed to 1/250 sec, you're allowing half as much light to get through to the sensor. Change it once more to 1/500sec and you're halving this again, and then another halving would be 1/1000sec, and so on.
Each time you halve it, or go in reverse and double it, you're moving by what's known as one 'stop'. So, a shutter speed of 1/125sec is one stop brighter than 1/250sec, as you're letting in twice as much light.
As you should be able to see when you adjust this, there are other settings in between these. Most mirrorless cameras and digital SLRs tend to move in third-stop increments, so you end up going from 1/125sec to 1/250sec via 1/180sec and 1/200sec options.
Photography cheat sheet: shutter speeds
If you ever use Manual exposure mode or exposure compensation, you may already be familiar with this idea of stops. Each dot or line on the exposure scale inside your viewfinder (or on your LCD's display) represents a third of a stop, and a more pronounced line indicates a full stop.
Unless you're using exposure compensation, the marker underneath these shouldn't move in the Shutter Priority mode as your camera will automatically be adjusting the aperture to compensate for whatever changes you make. The aperture also moves in full-stop and third-stop increments, and as you change shutter speed, the aperture either adjusts automatically or needs to be adjusted, in order to keep the exposure balanced.
So, if you choose a very fast shutter speed, your aperture will need to be wider in order to let in the same amount of light as if you were using a slower shutter speed (assuming you have your ISO fixed to a certain setting, rather than auto).
If you want to know more about what kinds of shutter speeds are appropriate for different kinds of images, check out this cheat sheet to which shutter speed should you be using.