Shutter Priority Mode

Shutter Priority MOde Gives you the most control over your shutter speed

Shutter Priority Mode (Tv or S) works just like Aperture Priority Mode except the dial operations are reversed.   The main dial (by the shutter release) controls the shutter speed.  You set the shutter speed you want and the camera will choose the aperture that it believes will give you the right exposure.  You dial in your exposure compensation, either by turning the second dial or by holding down a button and turning the same dial by the shutter release.

This shooting mode has some very useful purposes.  Whenever you care more about the shutter speed of your camera than the f/stop, consider using this mode.  Here are some possible applications:

1. Panning shots.  Perhaps you've seen photographs where a fast moving subject (car, bike) is in focus but the background shows a lot of motion blur.  This is achieved by choosing a relatively slow shutter speed and panning with the moving subject.  The camera movement tracks with the moving subject, allowing it to be relatively sharp, while the background is completely blurred by the camera's movement.  For this to work, it's best to find the shutter speed that works best for the situation and set it in shutter priority mode.
2. Flash Sync Speed.  Your camera has to sync the time the shutter is open with the flash when it fires.  If your shutter speed is too fast, the shutter will block the light from the flash from exposing the sensor. Now some flashes have the ability to compensate for this with "high speed sync," but most internal flashes on SLRs do not.  So when your flash is on, if the camera needs a shutter speed faster than its sync speed, it will only fire at its sync speed, and you will get overexposed images.  One solution is to switch to shutter priority mode and set the sync speed of your camera (like 1/250sec), and let the camera choose the f/stop that gives you the right exposure.  Check your camera manual to find the sync speed of your camera, and if you have an external flash, check to see if it has a "high speed sync" feature.
3. Waterfalls.  If you know you want to shoot your waterfall at a 2 sec exposure, you can set it in shutter priority mode and let the camera choose the f/stop.  Be careful though; if the scene becomes brighter, there may be no f/stop small enough for you to get a proper exposure, even at ISO 100, and you may begin to overexpose your image.

Note of caution.  Be very careful about setting very fast shutter speeds or very slow shutter speeds in changing light conditions. As light conditions change, it may be that there is no f/stop that will give you proper exposure at the shutter speed you've chosen.  For instance, suppose you are out shooting birds on a bright sunny day, and you use shutter priority mode to set an exposure of 1/2000sec.  If clouds roll in, your scene may become dark enough that even at your largest aperture (smallest f/stop), you simply can't shoot at 1/2000sec and properly expose your image.  You can compensate for this by raising your ISO or slowing down your shutter speed.