This document discusses aperture and how it controls both the amount of light entering the camera and depth of field. It explains that depth of field refers to the zone of sharp focus, with a large aperture giving a shallow depth of field and small aperture a deep depth of field. It instructs the reader to take photos in London or St Albans using different f-stops to see these effects, and provides tasks to complete by October 3rd involving ISO photographs, a photographer study, and capturing photos exploring depth of field.