Semi Automatic Modes

Now that we’ve learned how exposure works, and how to take pictures controlling that exposure in manual mode (M), Let’s take a look at two of the semi-automatic modes that come on our DSLRs, Aperture Priority and Shutter Priority.

Aperture priority is a semi-automatic mode in which you choose the aperture (how wide you open the eye of your camera), and your camera will automatically calculate the corresponding shutter speed for each picture. When you choose an aperture setting in aperture priority mode, it becomes “locked in” and your camera will automatically change just the shutter speed to match.  Aperture priority is usually referred to as Av on Canon cameras and A on Nikon cameras.

Why would you use aperture priority mode? The answer, usually, is depth of field.

  • to achieve a narrow depth of field, either to isolate our subject from its surroundings, or to get a delicate look which emphasizes texture, you can use aperture priority to lock in a wide aperture (1.8, 2.8, 4…)
  • to achieve a wider depth of field, in landscapes, or to show a subject more completely in its surroundings, you can use aperture priority to lock in a narrow aperture (18, 22, 28…)

Why would you use shutter priority mode? Shutter priority is useful if you’re taking photos of moving subjects and are concerned with motion blur.

  • to achieve a motion blur on moving objects, use shutter priority to lock in a lower/slower shutter speed (30, 60, 125…)
  • to achieve a stop-motion or stop-action effect, use shutter priority to lock in a high/fast shutter speed (500, 1000, 2000….)

Suggested Activities:

Take five pictures for each of the following. Set your camera to 400 or 800 ISO and shoot outside in daylight.

  • aperture priority to achieve low DOF
  • aperture priority to achieve high DOF
  • shutter priority to achieve motion blur
  • shutter priority to achieve stop-action

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