Our ability to perceive depth in pictures relies on visual cues, the most prominent being the relative size of objects. It should come as no surprise that the lens used to take a photograph can have a dramatic effect on our perception of depth. Pictures taken with wide-angle lenses differ significantly from those made with long-focus lenses. The quintessential wide-angle photo exaggerates the size of foreground objects in comparison to objects that are slightly farther away from the camera. Conversely, long-focus lenses appear to compress the apparent distances between widely spaced objects, causing them to appear much closer to one another than in reality. These properties are commonly described using the terms “wide-angle perspective” and “telephoto perspective,” respectively; the general term for these phenomena is “perspective distortion.” Unfortunately, the concepts of perspective and distortion are often misunderstood, even by veteran photographers.
In photography, perspective is your camera’s point of view and is determined exclusively by the position from which a photograph is taken. The focal length of a lens doesn’t directly influence perspective. Whether using a 16mm ultra wide-angle lens or a 90mm long-focus lens, the camera’s position is the only thing that controls perspective.
The characteristics attributed to perspective distortion are entirely a consequence of the size of the subject(s) and the camera-to-subject distance. When an object halves its distance to your camera, it will appear to double in size along its linear dimensions (its subtended visual angle is doubled). Conversely, when an object doubles its distance from the camera, it will appear half in size along its linear dimensions (its subtended visual angle is halved).
Perspective distortion and focal length
Although focal length doesn’t directly cause perspective distortion, it’s often blamed for the effect for two reasons. First, different focal lengths are used for different purposes and at varying subject distances. Wide-angle lenses are typically used from shorter distances, lest the subject appears too small in the picture, while long-focus lenses are generally used from farther away.
Second, the effects of perspective distortion at the extremes of near and far are betrayed by short and long focal lengths. For example, if you wanted to capture the “wide-angle perspective” caused by a short camera-to-subject distance, you would need a wide-angle lens, because the angle of view of a normal (or longer) lens would be too narrow to render the effect in its entirety. Likewise, if you wanted to witness “telephoto compression,” you would need a long-focus lens because the effect would be rendered too minuscule within the angles of view of wide-angle and normal lenses. Thus, a lens’s focal length makes the effects of perspective distortion evident, but it absolutely doesn’t cause them.
Perspective and portraiture
The short working distances used with wide-angle lenses can exaggerate subject features and show distractions in the background. Compared to short-focus lenses, the perspectives (i.e., subject distances) used with long-focus lenses to achieve the desired composition can render people more flatteringly; they also permit greater control of background elements due to their narrower angle of view and depth of field.
What is the ideal perspective for portrait photography? The social sciences offer several clues about favourable camera-to-subject distances. Consider the idea of interpersonal distance zones, which are divided into the intimate (0–45 cm), personal (45 cm to 1.2 m), social (1.2 m to 3.7 m), and public (3.7 m and greater) distances. While these specific ranges may not apply to you—they are from a 1966 study conducted on American men—you likely have an approximate notion of comfortable interpersonal distances. Most of our interactions with others occur in the social range, while most of our non-interactive experiences happen in the public range. The average of these distances may act as a guide for the ideal perspective for portraiture, because it takes into account the typical distances at which individuals are exposed to the faces of others, thereby normalizing it.
Furthermore, this can be used to exploit emotional responses to portraits. A close perspective is more intimate, a far one more distance, and a medium one more typical.