Since last lecture, you have known an important element in Photography: the Exposure Triangle. You learn that the aperture value controls depth of field. In fact, there are
2 more critical factors affecting depth of field.
FACTOR 1: THE FOCUS DISTANCE
Focus distance is a calculation from the subject to lens. By changing the focus distance, you will get different depth of field of an image. If you are closer to the subject you are focusing on, you will have an image with shallower depth of field, and vice versa.
FACTOR 2: THE FOCAL LENGTH
Focal length (usually measured in mm) is a calculation of an optical distance from the convergence point in the lens to the sensor or film inside the camera, but IS NOT the actual length of a lens. Basically, the longer the focal length, the narrower the angle of view and the more magnifying effect in your picture with shallower the depth of field, and vice versa.
**Shallower lens (e.g. 200mm) → longer focal length→ shallower view captured + shallower depth of field → telephoto effect
**Wider lens (e.g. 28mm) → shorter focal length → wider view captured + deeper depth of field