Do Wide Angles Distort Perspective?
It’s a common opinion that a standard lens provides an image with a "correct" perspective, while other focal lengths, particularly wide angles, distort perspective.
Do Wide Angles Distort Perspective?
A Small Experiment
It’s a common opinion that a standard lens provides an image with a "correct" perspective, while other focal lengths, particularly wide angles, distort perspective.
Camera lenses are used to efficiently project an image of reality onto an image plane, such as a sensor or film. Lenses gather all light rays according to a principle called polar projection. This means that the projection occurs through a point, the optical center of the lens.
To explore how focal lengths and perspective interact, let’s consider a simple experimental setup. We’ll stick to rectilinear lenses, not fisheye lenses, and disregard optical aberrations like barrel or pincushion distortion, as these are negligible or minor in modern lenses.
Imagine standing at the red point on a vast, flat, horizontal grass field. Ahead of us, three cubes measuring 5x5x5 meters each are placed. We face the rightmost cube, with our eyes 1.5 meters above the ground.
To draw a polar projection of what we see, we place a transparent plastic sheet in front of us as our image plane.
Using very long pens and brushes, we remain at the red point and draw the cubes on the plastic sheet exactly as we see them. This is essentially how a lens operates, except that it flips and inverts the image onto an image plane behind the red point. When flipped back, the results are identical.
The distance from the eye point to the image plane corresponds to the lens’s focal length. Some might object, noting that lens focal lengths are typically measured in millimeters rather than meters. However, this doesn’t affect the results, aside from scaling the image. We could place the plastic sheet 50 mm from our eyes, and get exactly what a camera with a 50 mm standard lens would se.
For pedagogical clarity, we use a larger focal distance for illustration purposes.
Upon completion, the image resembles Fig. 3. As seen, the cubes become increasingly elongated and less cubic the farther they are from the center of the image. Yet, considering how they were constructed, the depiction is an exact representation of reality, free of perspective inaccuracies.
The perception of distortion arises entirely from the image being too small or viewed from an incorrect distance. If we position our eyes at the same distance from the image as the red point was from the image plane, the perspective will appear correct. Enlarging the image by a factor of five requires increasing the viewing distance by the same factor for accuracy. The leftmost cube, which appears elongated, would then be seen at a sharp angle to the paper, removing the elongated appearance.
The experiment’s conclusion is that all rectilinear lenses accurately represent reality (excluding negligible optical errors). Perspective remains unchanged; different focal lengths (or sensor or film formats) merely affect the amount captured in the frame. Perspective changes only when the camera is moved or rotated, and this happens in the same way with all lenses.
Size Matters
Standing close to large wide-angle images often creates a sense of ‘being there’. They occupy a significant portion of the visual field, and the short viewing distance relative to image size ensures correct perspective. Conversely, images captured with telephoto lenses often feel flat, as the large size relative to the correct viewing distance hinders depth perception.
For example, if one photographs for an exhibition using a full-frame camera and various lenses, aiming for those correct perspectives. Let’s suppose that visitors to the exhibition view the images from 1 meter distance.
An 18 mm super wide-angle image should be printed large, e.g., 200x133 cm, for maximum impact.
A 35 mm lens results in a suitable print size of 103x69 cm (or the standard 100x70 cm).
A 50 mm standard lens produces a 72x48 cm image.
A short telephoto lens (105 mm) creates a 34x23 cm image.
A long 400 mm telephoto lens) yields a perspective-accurate print of just 9x6 cm, explaining why telephoto images often appear compressed at standard sizes and viewing distances.
The purpose of this essay isn’t to assert that perspective-accurate images are a necessity. On the contrary, leveraging perspective distortions from incorrect viewing distances can be quite striking. However, it’s worth considering that a precisely rendered perspective can evoke a profound sense of presence. A perspective-accurate image on matte or glossy paper with optimal lighting and no reflections can feel so three-dimensional that one might be compelled to reach out to confirm the paper’s surface.
A fine example of such immersive imagery is Nick Brandt’s African wildlife portraits , showcased at Stockholm’s Fotografiska Museum years ago. Unlike most wildlife photographers, Brandt avoided long telephoto lenses, opting instead to photograph animals at closer distances with standard focal lengths. I remember that strong feeling of ‘being present’ when I saw the large photographs.
"Well, in any case, I think it's time to debunk the myth that wide-angles per se distort perspective. It's when the focal length and the viewing distance of the final image don't match that the perspective appears distorted."
© Jan Lindahl 2024
Odensbacken, 2024-11-20
Jan Lindahl