David Hockney (1937- ) Lord Rothschild 1999, pencil and white chalk on grey paper

In March 1999, after visiting an Ingres exhibit, Hockney began to make portrait drawings using the camera lucida. This nineteenth century device is a small prism with two lenses mounted over a sheet of paper to allow the artist to see both subject and paper superimposed. The artist can then see their drawing hand moving over the outlines of the subject and record the prominent features before elaborating the picture.

In 1987, Queen Elizabeth II revived the tradition of commissioning portraits of members of the Order of Merit - this work is the latest of those portraits, having been presented by the artist in 2003.

Hockney believes that optical devices caused a revolution in realism during the fifteenth century and that they were very important for the development of painting - this is a theory that has not yet met with universal acceptance.