Notes based on Steadman's essay on the Camera Obscura

Notes based on Philip Steadman's book on "The Camera Obscura" from Vermeer's Camera: Uncovering the Truth Behind the Masterpieces. [Oxford University Press, 2001]

The term camera obscura was coined by the astronomer Johannes Kepler in the 17th century.

Definition - If a small hole is made in the wall of a darkened room, an image of the scene outside can be formed by light rays passing through the hole.

Aristotle watched an image of the sun formed beneath a tree becominmg crescent-shaped during an eclipse. This led to the camera obscura's main application - watching solar eclipses without damaging one's eyes.

8th century Chinese philosophers studied how images are formed by light as it passes through small apertures.

The 10th century Arabic scholar, Alhazen, studied these types of image formations, which later influenced the 13th century English writers Robert Bacon and John Pecham and the Polish philosopher Witelo.

Pecham wrote about solar optics in his 1279 treatise Perspectiva Communis (Natural Optics).

The first published illustration of a camera appears in a book in the 16th century by the Dutch astronomer and mathematician Reinerus Gemma Frisius and shows an image of a solar eclipse he observed at Louvain in 1544.

Prior to this, the 1490 notebooks of Leonardo da Vinci hints possible use of the camera obscura.

In the 16th century glass lenses were introduced in place of pinholes. This created larger apertures and brighter images. Convex lenses used in spectacles for correcting long-sightedness can be traced back to the end of 13th century Italy.

Girolamo Cardano, a Milanese physician and natural philosopher, is sometimes credited with the earliest written description of a camera with a lens. Reference De Subtilitate, 1550. It was argued by Major-General Waterhouse that Cardano was referring to a concave mirror as opposed to a lens.

Soon afterwards, Daniele Barbaro, a Venetian patrician writes about cameras with convex lenses in 1568. Another Venetian, Giovanni Battista Benedetti, writes in 1585 about "a method for correcting the inversion of the image, by setting a plane mirror at 45 degrees to the direction of the light coming from the lens." This arrangement later appears in late 17th century portable box cameras.

In the 16th century, a Neopolitan professor named Giovanni Battista della Porta wrote the compendius Magia Naturalis describes the camera obscura and the use of convex lenses and concave mirrors.

Around 1600 Kepler collaborated with Tycho Brahe, who used the camera obscura for astronomical purposes. In Kepler's writings, he discusses this use of the lens as well as surveying. Moreover, Kepler discusses the use of two convex lenses in a camera, "spaced a suitable distance apart."

"Sun spots" are mentioned in the 1630 treatise, Rosa Ursina sive Sol by Christopher Scheiner. These are discovered when combining a telescope with a camera obscura to create a "projecting telescope."

In 1620 in Linz, Austria, Kepler showed a portable camera obscura of his own design to the English diplomat Harry Wotton. This instrument was later described in a letter to Francis Bacon as he thought that "there might be a good use made of it for Chorography..."