Why does a wide-angle lens distort faces at the edges?

Because a flat sensor records a wide cone of view, so shapes near the frame edge are stretched away from the centre. It is geometry rather than a defect, and it grows with the angle the lens covers.

The effect is strongest exactly where wide-angle lenses are most useful, which is why it surprises people who assumed it was a fault.

The geometry

A rectilinear lens keeps straight lines straight, and the price is that angular distances near the edge of a wide field occupy more of the frame than those at the centre. A sphere — a head — near a corner is therefore drawn out along the line away from the middle.

Why it grows with the angle

Wider coverage means a larger cone projected onto the same flat rectangle. In this catalogue the widest fixed focal lengths print 11 mm, 12 mm and 16 mm, and the effect at the corners of those is pronounced; the standard focal lengths around 35 mm and 50 mm show almost none.

What it is not

Not a property the format changes: the engraved focal length is the lens, and a smaller sensor takes a narrower rectangle out of the same projection, which crops away the worst of the corners rather than fixing them.

What software can and cannot do

It corrects curved lines reliably, because those are a lens fault with a measurable profile. It cannot undo the projection without curving what was straight — a choice between two distortions rather than a repair.

Where this page and the maker’s own manual disagree, the manual decides. Every focal length, aperture, guide number, stop of stabilisation, load rating and sealing claim on this page is reported from the manufacturer’s own documentation, with its unit written as published, and named as such — none of it is measured here. An engraved figure is reported as the maker engraves it, and is never restated in another convention, because the two are not the same number. And the statement repeated rather than assumed: an equivalent focal length is arithmetic, not a measurement. The millimetres engraved on a barrel describe the optic itself and never change; what changes is how much of the projected circle a given sensor takes out of it. An equivalence is that ratio applied to the engraved figure, and it appears here as a calculation with its format named, never in place of the number on the lens.