Canon PowerShot G12 Motion and Depth of Field

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Distinct characteristics are related to changes in aperture and shutter speed. Shutter speed controls the length of time the light strikes the sensor; consequently, it also controls the blurriness (or lack of blurriness) of the image. The less time light hits the sensor, the less time your subjects have to move around and become blurry. This can let you impose some control, like freezing the motion of a fast-moving subject (Figure 2.10) or blurring subjects to give the feel of energy and motion (Figure 2.11).

The aperture controls the amount of light that comes through the lens, but it also determines what areas of the image will be in focus. This is referred to as depth of field, and it is an extremely valuable creative tool.

A fast shutter speed and high ISO froze the action mid-swing. [Photo: Jeff Carlson]

The slower shutter speed, combined with the camera’s neutral density filter, shows the flow of water across the rocks. [Photo: Jeff Lynch]

The smaller the opening (the larger the number, such as f/8), the greater the sharpness of objects from near to far (Figure 2.12). A large opening (or small number, like f/2.8) means more blurring of objects at distances other than your subject (Figure 2.13).

By using a small aperture, the area of sharp focus extends from a point that is near the camera all the way out to distant objects. [Photo: Jeff Carlson]

Isolating a subject is accomplished by using a large aperture, which produces a narrow area of sharp focus. [Photo: Jeff Carlson]

As we further explore the features of the camera, you will learn not only how to utilize the elements of exposure to capture properly exposed photographs, but also how you can make adjustments to emphasize your subject. It is the manipulation of these elements—motion and focus—that will take your images to the next level.

Limited Aperture Range

If you’re accustomed to using a DSLR, you may be scoffing at the f/8 aperture limit of the G12. In that realm, f/8 falls in the middle of the scale (peek at the tables a few pages back to get an idea). However, the G12 doesn’t have the luxury of swapping lenses like a DSLR. To keep the camera compact and use a single built-in lens, a broader aperture range was
sacrificed. That said, the camera does a good job of maintaining sharpness from near to far using f-stops as low as f/4 or f/5.6—settings that represent the wide-open end for many DSLR lenses.