Optical aberration where straight lines curve at frame edges — barrel (wide lenses) or pincushion (telephotos). Signature of every lens; correctable in post or embraced for style.
Every lens distorts. This is not a flaw, but an optical reality—and anyone who ignores it will run into problems when matching shots or with visual storytelling. Lens distortion occurs because the focal length is not constant across the entire image field. Light is refracted differently at the edges than in the center of the image, and straight lines—horizons, building edges, door frames—become curves. When shooting, you have to accept this or use it deliberately.
Barrel distortion—also called positive distortion—typically occurs with wide-angle lenses and fisheye lenses. The image edges bulge outward, making the space appear inflated. You see it immediately: a rectangular door frame becomes a barrel. In practice, this can look spectacular—skateboard videos, action sequences, extreme perspectives benefit from it. But be careful when framing faces or cutting between shots with different wide angles. The discontinuity will directly bother the eye. Pincushion distortion—negative distortion—is the opposite: telephoto lenses and long focal lengths push the edges inward. A rectangular room becomes a cushion. This looks less dramatic optically, but is just as problematic for shot matching.
On set, the first thing you should do is know your lens's distortion. This is not a minor issue—it determines how you will frame, how the camera translates reality. With classic lenses like the old Zeiss lenses, distortion is characteristic and part of their look. Modern zooms have variable distortion across the zoom range—another reason why zoom shots are problematic in documentaries. They appear unstable because lines curve and straighten again during the zoom.
In post, it's simple: every digital intermediate suite has lens correction tools that can remove or add distortion. But beware—correction means cropping and image degradation, especially with extreme distortion. Some DoPs deliberately don't correct to preserve the optical characteristics of the glass. Others correct everything to a neutral baseline. You make the decision during the shoot. If you want to cut between multiple lenses, you have to consider the distortion or correct it consistently—inconsistency is what's annoying, not the distortion itself.