Canon PowerShot G12, Av: Aperture Priority Mode

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You wouldn’t know it from its name, but Av mode is one of the most useful and popular of the Creative modes. Av stands for Aperture Value and, like Time Value, it’s another term that you’ll never hear a photographer toss around. The mode, however, is one of my personal favorites, and I believe that it will quickly become one of yours as well. Av, more commonly referred to as Aperture Priority mode, is also deemed a semi- automatic mode because it allows you to once again control one factor of exposure while the camera adjusts for the other.

Why is this one of my favorite modes? It’s because the aperture of your lens dictates depth of field. Controlling depth of field lets you direct attention to what’s important in your image by specifying how much area in your image is sharp. If you want to isolate a subject from the background, such as when shooting a portrait, a large aperture keeps the focus (literally) on your subject and makes both the foreground and background blurry. If you want to keep the entire scene sharply focused, such as with a landscape scene, then using a small aperture will render the greatest amount of depth of field possible.

When to use Aperture Priority (Av) mode

  • When shooting macro, or close-up, photography (Figure 4.6)
  • When shooting portraits or wildlife (Figure 4.7)
  • When shooting architectural photography, which often benefits from a large depth of field (Figure 4.8)
  • When shooting most landscape photography

Aperture priority helps keep the foreground image in focus in macro photos. [Photo: Lynette Coates]
Figure 4.6 Aperture priority helps keep the foreground image in focus in macro photos. [Photo: Lynette Coates]
A large aperture created a blurry background so all the emphasis was left on the subject. [Photo: Anneliese Voigt]
Figure 4.7 A large aperture created a blurry background so all the emphasis was left on the subject. [Photo: Anneliese Voigt]
Using the camera’s smallest available aperture provides a large depth of field. [Photo: Jeff Carlson]
Figure 4.8 Using the camera’s smallest available aperture provides a large depth of field. [Photo: Jeff Carlson]
F-stops and aperture

As discussed earlier, when referring to the aperture value, you will find it described as an f-stop. The f-stop is one of those old photography terms that, technically, relates to the focal length of the lens (e.g., 200mm) divided by the effective aperture diameter. These measurements are defined as “stops” and work incrementally with your shutter speed to determine proper exposure. Older camera lenses used one-stop increments to assist in exposure adjustments, such as 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, and 22. Each stop represents about half the amount of light entering the lens iris as the larger stop before it. Today, all adjustments to this setting are performed via the camera’s electronics. The stops are also now typically divided into 1/3-stop increments to allow much finer adjustments to exposures.

So we have established that Aperture Priority (Av) mode is highly useful in controlling the depth of field in your image. But it’s also pivotal in determining the limits of available light that you can shoot in. The larger the maximum aperture, the less light you need in order to achieve an acceptably sharp image. You will recall that, when in Tv mode, there is a limit at which you can handhold your camera without introducing movement or hand shake, which causes blurriness in the final picture. A larger aperture lets in more light at once, which means that you can use a faster shutter speed. On the other hand, bright scenes require the use of a small aperture (such as f/8), especially if you want to use a slower shutter speed. That small opening reduces the amount of incoming light, and this reduction of light requires that the shutter stay
open longer.

Setting up and shooting in Av mode

  1. Turn your camera on and turn the Mode dial to Av.
  2. Select your ISO by rotating the ISO dial.
  3. Rotate the Front dial to choose an aperture setting, which appears at the bottom of the LCD. Roll the dial to the right for a smaller aperture (higher f-stop number) and to the left for a larger aperture (smaller f-stop number).
  4. Point the camera at your subject and then activate the camera meter by pressing the shutter button halfway to preview the exposure. As with the Shutter Priority mode, the orange light by the viewfinder will blink if the image is underexposed or overexposed.
  5. Release the button and adjust the Front dial to change the setting.
  6. Press the shutter button fully when you’re ready to shoot.