Intermediate Photography Lesson 4 Quiz | Test Your Knowledge

Shallow depth of field requires a wide aperture, a long focal length, and close subject distance. f/2.8 is wider than f/4, f/8, or f/11; 85mm is longer than 35mm, 50mm, or 24mm; and 2 meters is closer than 3 or 5 meters. All three factors combine to produce the shallowest result.

The hyperfocal distance is the focus point at which depth of field reaches infinity while extending as close to the camera as possible. Focusing there at a moderate aperture such as f/8 to f/11 keeps both the nearby flowers and the mountains sharp. Focusing on the mountains wastes much of the near depth of field.

The look of out-of-focus highlights comes from the lens. Each blurred point takes the shape of the aperture opening, so a few straight blades make hexagons or other angular shapes, while many rounded blades give smooth circles. The optical design also decides whether the edges of those discs look soft or harsh.

Light spreads out slightly as it passes through a very small opening, turning each point into a tiny blur. This diffraction softens fine detail across the whole frame, so at f/16 many lenses look less sharp than at f/8 even though depth of field is greater. Sensors with smaller pixels show it sooner.

At f/1.8 with an 85mm lens at 1.5 meters, depth of field is only about 3 centimeters, too thin for both eyes and ears. Stopping down to f/4 or f/5.6 increases it to roughly 7 to 10 centimeters, enough to cover the face from eyes to ears while still blurring a distant background.

Focus stacking means taking several photos with focus moved slightly between each, then blending the sharp parts in software. The result is sharp over far more depth than one exposure allows, which is useful in macro, product and some landscape work where even small apertures fall short or soften from diffraction.

Three rows stand at different distances, and f/4 with a 50mm lens may not give enough depth of field to cover them all. Stopping down to f/8 roughly doubles the depth of field so the back row falls inside it. Focusing about a third of the way into the group spreads that depth best.

Depth of field depends on aperture, focal length, subject distance and sensor size. ISO only changes how much the sensor's signal is amplified, which affects brightness and noise, not which distances are in focus. It matters only if raising or lowering it leads you to change the aperture.

Depth of field shrinks rapidly as focus distance shortens, roughly with the square of that distance. At the very close range needed to fill the frame with a watch, even f/16 may cover only a few millimeters. Focus stacking is the usual solution.

Background blur grows as the background gets farther from the subject. Moving the subject well away from the background, and getting closer to the subject, puts the background further outside the depth of field so it blurs more. A smaller sensor would give more depth of field, the opposite of what is wanted.