What is Shutter Priority?

I've had this question asked a few times, so here's a quick post that hopefully explains what it means and why it's useful. I'll post similar on the other modes soon (aperture priority, program, and manual)

What is Shutter Priority?

In a nutshell, Shutter Priority is a setting on many cameras (both digital and film) where the user sets the shutter speed and the camera then adjusts the aperture automatically to get a correct exposure.

On most cameras, Shutter Priority is enabled by putting the main control dial in "S" (Nikon) or in "Tv" (Canon), which stands for "Time value", meaning you set the "time" the shutter will be open.

How does Shutter Priority work?

Once you set the camera to Shutter Priority and have chosen the shutter speed you want, the camera will use its internal light meter to determine the appropriate aperture required for a correct exposure given the available light. So, the aperture will be variable but the shutter speed will remain constant on what you've set the camera to.

Why is Shutter Priority important?

Because it allows you, the photographer, to decide what shutter speed is needed to get the effect you're after. This mode is useful when motion blur is important, either the existence or lack of. For example, if you're shooting sports and you want to ensure you freeze the action, you may want to set the camera to Shutter Priority and select a shutter speed of, say, 1/500th of a second. Then let the camera pick the aperture without having to worry about it. On the flip side, imagine you're shooting a waterfall and want the water to appear blurred to get that silky-looking effect. Then you'd set the camera on a low shutter speed, say 1/8th of a second, and let the camera worry about the aperture.

One caveat though, remember to check that there is enough light for the camera to actually be able to get a correct exposure! For example, if a correct exposure using a shutter speed of 1/1000th is F1.8 and the widest aperture your lens can get to is F5.6 you will get an underexposed image. You can learn more about aperture, shutter speeds, and exposure in other articles.