Depth of Field: Focal Length Exercise
To understand the effect of focal length on depth of field, take a series of shots with a zoom lens. Start at the longest focal length of the lens, compose a shot with a subject in the foreground. With each shot widen the lens and step in closer to your subject, positioning the subject in approximately the same place each time. As you widen the lens more and more of the photo will be in focus. Compare photos and metadata on your computer.