Portrait of a man
Rembrandt made nearly 100 self-portraits from the 1620s until his death in 1669, including around 50 paintings as well as dozens of etchings and drawings. This Rembrandt self-portrait in oil on canvas from 1659 is nearly life-size, and the researchers think it was painted from an optical projection created by a specific arrangement of a curved mirror and a flat mirror.
Projecting an image
The research includes a detailed analysis of the combinations of flat and curved mirrors, or flat mirrors and lenses, which can be used to replicate the proportions, perspectives and lighting seen in Rembrandt's self-portraits.
As his experiments proceeded, he used larger mirrors to obtain a larger image and a copper etching plate as a brighter projection surface, shown in this image.
A second flat mirror combined with a refracting lens can be used in place of the concave mirror.
At right, "Rembrandt laughing" is a self-portrait painted in oil on copper in 1628 and measures 8.7 by 6.7 inches (22 cm by 17 cm).
The researchers were able to make clear projections of similar sizes with concave mirrors of focal lengths between 5.5 and 9.8 inches (14 and 25 cm).
In the early 16th century, for example, Da Vinci wrote about the use of the camera obscura, a primitive type of camera that uses a hole in the wall of a darkened room as a lens to create an upside-down projection.
The reversed image, created by a camera obscura, is shown in this illustration from a 17th-century manual on military arts, which included geometry and mechanics.
This painting, "Self-portrait with two circles," is one of Rembrandt's last, and was painted in oil on canvas between 1665 and his death in 1669.
It shows a "soft focus" effect, with strong light and strong detail around the face of the artist, but low detail and softer light towards the edges. The researchers say the same effect is seen in projections made with a flat and a curved mirror.