Final answer:
Open depth of field refers to images where a large portion is in focus, achieved using a small aperture, while shallow depth of field means only a small part is in focus, which is achieved using a wide-open aperture.
Step-by-step explanation:
An open depth of field, also referred to as a deep or large depth of field, means that a large portion of the photograph, from the foreground to the background, is in focus. This is typically achieved by using a smaller aperture (represented by a higher f-stop number) which allows for more of the scene to appear sharp. An example of this could be a landscape photo where both nearby trees and distant mountains appear clear.
A shallow depth of field, on the other hand, is when only a small part of the image is in focus, with the rest being progressively more blurred. This effect is created by using a wide-open aperture (lower f-stop number), which results in a narrow plane of focus. This technique is often used to isolate a subject from its background, such as in a portrait where the person's face is sharp while the background is soft and out of focus.