Paul GrahamVerified account

It has to do with the shutter speed and the changing of light, faster shutter speeds when in the lighter spot. Would happen with film camera, could look slightly different though

Doesn’t the AC light at 50hzs and shutter speed cause this effect.

Only in electronic sensors where the frame is scanned progressively (left to right or up to down). Won't happen in film cameras.

It’s probably an exposure time artifact, so you could probably recreate on film.

By default, cellphone cameras adjust exposure timing based on pixel readout values. A DSP/SW engineer can modify the FW to use fixed timing and remove this effect. Conversely in film cams, an operator would need to dynamically adjust the shutter speed to achieve this effect

It does happen in film cameras as well, though not to as an extreme a level. Even your own eye can realize this effect, though again not to this extreme a level. This is due to digital cameras offering much faster shutter speeds than most films can accept.

It’s an artifact of the hardware of cellphone cameras, they capture images one line at a time. To get an interesting effect, they tuned the ruler length.

Depends on if the camera has a global shutter or rolling shutter. With a global shutter you would see a frozen or slowmo movement, with a rolling shutter you get the effect from the video. Most cinema cameras have a global shutter afaik.