Pincushion Distortion (C) Wikipedia

See
Barrel Distortion

see camera obscura.

A kind of vignetting which occurs exclusively with digital cameras.

Possible causes are:

• the pixels are not completely flat due to construction on the sensor surface, but in small cavities. Too shallow light cast shadows on the edges of the pixels, like the evening sun at some point no longer reaches mountain valleys.
• The sensor uses micro-lenses (small converging lenses) to capture as much light as possible for each pixel. From a certain off axis angle lenses are no longer capable to deflect the light strong enough and the light can’t reach the pixel no more.
• With image side telecentric lenses such vignetting does not occur because the incident light rays are parallel to the optical axis.
  The latest sensor technologies however try to correct the Pixelvignettierung on-chip (= directly in the sensor) or by micro lenses that have differently shape in the corners than in the center.
  Thus it may happen that the image side telecentric lenses surprisingly show vignetting.