Shutter Priority is one of four common User Control Shooting Modes in which the user has increased control over the exposure variables of ISO, Shutter Speed, and Aperture. 
This is one of two ideal shooting mode for action photography when the user wants motion to be frozen. (The other is Manual Shooting Mode).
In Shutter Priority the user sets the desired Shutter Speed, and the camera balances the exposure with a corresponding Aperture value. NOTE: The user also pre-selects the desired ISO (according to available light). Stop Action photography is most often used in wildlife and sports photos, but can also be used in good lighting situations to force your camera to select a wide aperture. Remember, fast shutter speeds allow light to hit the sensor for only a brief time, therefore the lens opening has to be wide to allow in an suitable amount of light.
CONSIDERATIONS
- FASTEST SHUTTER: In good lighting you can elevate the ISO to about ISO 800 (depending on your camera’s *noise threshold*) to achieve super-fast shutter speeds foR action like ball sports, waterfalls, or birds.
- SHALLOW DOF: Cameras often need to select the widest possible aperture to achieve the user selected shutter speed. For this reason, know that your DOF will be shallow.
- NOISE: In low-light situations ISO often needs to be elevated to allow for a fast shutter. This can introduce digital image noise.
- LENS OPENING: Though the camera selects the corresponding aperture, the aperture range is limited by the maximum aperture of the camera lens. Some zoom lenses often change aperture when zooming in and out. This can result in bright enough images when zoomed out, but too-dark images zoomed in.
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