Canon 7D Motion and Depth of Field


There are distinct characteristics that are related to changes in aperture and shutter speed. Shutter speed controls the length of time the light has to strike the sensor; consequently, it also controls the blurriness (or lack of blurriness) of the image. The less time light has to hit the sensor, the less time your subjects have to move around and become blurry. This can let you control things like freezing the motion of a fastmoving subject (Figure 2.11) or intentionally blurring subjects to give the feel of energy and motion (Figure 2.12).

This little boy was waving the fl ag back and forth very quickly, so I used a faster shutter speed to freeze the action.

Using a slow shutter speed with a fast-moving subject will intensify the feeling of movement in an image.

The aperture controls the amount of light that comes through the lens, but also determines what areas of the image will be in focus. This is referred to as depth of fi eld, and it is an extremely valuable creative tool. The smaller the opening (the larger the number, such as f/22), the greater the sharpness of objects from near to far (Figure 2.13).

I wanted all three people in this photo to be in focus, so I chose to use a small aperture.

A large opening (or small number, like f/2.8) means more blurring of objects that are not at the same distance as the subject you are focusing on (Figure 2.14).

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

A wide-open aperture created a shallow depth of fi eld for this photograph.