SSC: Find a square or rectangular subject and photograph it without perspective distortion.

Rectangles in the subject must also be rectangular in the image (I will pay particular attention to this.)
Application: For example, for a distortion-free architectural shot.

It is a challenge to have a 90° angle everywhere between the subject plane and the sensor plane.

A 20mm to 25mm micro 4/3 setting gives me the best photo without distortion.