Which factor most affects depth of field when shooting portraits?

• A. ISO
• B. Aperture size
• C. Shutter speed
• D. Focal length

Answer: (B)

Depth of field in portraits is controlled most directly by aperture size. Opening the lens to a larger aperture (smaller f-number) reduces the circle of confusion and narrows the range of distances that appear sharp, creating a blurred background that helps the subject stand out. Conversely, using a smaller aperture increases the depth of field, bringing more of the scene into focus.

Shutter speed and ISO affect exposure and motion blur, not the depth of field, so they don’t determine how much of the scene is in focus. Focal length also influences depth of field—longer lenses can produce shallower DOF—but the effect is often secondary to choosing the right aperture for the desired level of background blur in portraits.