pin-cushion.

A kind of curvilinear distortion where edges that would normally be recognised as being straight, say the top of a picture plane or a writing table, are curved. The distortion can occur towards the sun, where the outer portions of an image are seen from a stopped-down simple lens.

A rectangular picture plane can be seen. to resemble the shape of a pin cushion or pillow. A similar effect, say partially obtained from some selenium copier machines, when taking a copy from the middle of a thick book, where horizontal typeset lines take on the curve of the page made by the spine’s binding. This recalls the work Nam June Paik or the lens effect of the universe. That is where gravity can focus light to produce two or more images. For example, the quasar discovered in 1979 was first thought to be two. The illusion is created by an intervening galaxy acting as a gravitational lens.

Pin-hole distortion refers to defects in Gesso panels often due to over-dilute glue solution. Pin-holes were made by Renaissance painters to pounce, that is transfer, black chalk drawings onto primed canvas planes by pricking the chalk lines onto the planes. Using a pin-hole camera in the 1990s Dave Gepp made images of Venice which confirmed Canaletto’s lack of topological accuracy.