The centre of the lens is called the optical centre C. In a ray diagram, a converging lens is drawn as a vertical line with outward facing arrows to indicate the shape of the lens. Point the lens ...

This effect has different names. Some people call it ‘converging verticals’, some call it ‘keystoning’, after the shape of keystones in arches. Technically, it’s a type of perspective ...

The word “Schlieren” is German, and translates roughly to “streaks”. What is streaky photography, and why might you want to ...