A portrait captured on location with a 50mm lens at f/1.2 drives the viewer’s attention to the sharp subject’s face
BRIAN SAYS… Assuming you mean lenses with a large maximum aperture, they are often used by portrait photographers to separate a subject from the environment. Taking a portrait often means they are the most important element in the frame, and the differential focus between subject and background is one way to emphasize that. Eye-Detection AF makes such pictures far simpler to capture. An important factor for portrait lenses is bokeh (how out-of-focus areas are rendered), and large aperture lenses are prized for this. Sometimes portraits need show more environment than person, so a larger aperture may not always be needed.