The perspective is similar to what the human eye sees, so space is neither stretched nor squeezed. About 35–50mm on full frame.
When it needs to look unembellished, like a review or an interview; a baseline shot between wide-angle and telephoto shots.
Public AI example available — the Sora 2 guide's example prompt 'Lens: 40 mm spherical', and a third-party video that compares the 50mm setting in Higgsfield image generation.
50mm normal lens, natural human-eye perspective with no distortion, a woman shows a pair of headphones to the camera at a cafe table, medium shot at eye level, straight vertical lines and true-to-life proportions, locked-off camera, soft window light, honest everyday mood, 6-second shot.
50mm normal lens, natural perspective, no distortion, medium shot at eye level
Call Me by Your Name (2017) — Shot with only one lens (35mm) · Films directed by Yasujirō Ozu — He used a 50mm lens throughout his career