TEST CASE 5: Did Vermeer use a camera obscura?

As early as 1430, images could be projected using concave mirrors. By 1600, better images could be projected, more simply, using lenses. And then in 1650, the camera obscura projected even better images even more simply. The camera obscura functions as a room-size camera. A dark room contains a small hole (aperture) in one wall. An object is placed outside the dark room and its image is projected onto the back wall of the dark room, where an artist can trace it. Without making any adjustments, the artist traces a complete, accurate, two-dimensional image of a three-dimensional object.

Schematic cross-section of a camera obscura
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The size of the image, relative to that of the object, equals the relative distances of image and object from the aperture ( and respectively).

     size of image /size of object = /    (1)

Imagine that we can measure these four quantities for a particular painting. If these four measured quantities satisfy (1), the artist could have used a camera obscura. Following this approach, Philip Steadman has examined six of Vermeer's paintings to test if a camera obscura could have been used. The test involves the use of (1).

Vermeer's paintings

Johannes Vermeer (1632-1675) spent his working life in Delft. He died young and less than 35 paintings are attributed to him today. Mostly, his paintings are studies of domestic interiors, featuring not more than three people. Several of these domestic interiors show common features - casement windows (on the left-hand side of the room) and a tiled floor - and Steadman has deduced that these were painted in the same room, probably Vermeer's studio. The key painting in Steadman's analysis is Vermeer's painting The Music Lesson.

The Music Lesson, Vermeer, c. 1662-4
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Showing the reflection in the mirror on the far wall.
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Steadman determined the dimensions of the room using the tiles, calibrating the tile size against the known size of objects appearing in the pictures, such as the harpsichord. The back wall (behind the viewer) is reflected in the mirror of The Music Lesson. With the back wall located, Steadman was able to measure the length of the studio. This is ( + ). Next, for each painting, he had to determine , the distance between the object and the aperture. Omitting the details here, is measured from analyzing the geometric perspective of the painting.

Utilizing (1) and the quantities he determined, Steadman was able to predict the sizes of the images for all six paintings. Then he compared these predictions with the actual sizes of the canvases, obtaining astonishingly good agreement. It is significant that the canvases differed in size. Steadman's study extended over 20 years and it provides incontrovertible evidence that Vermeer used a camera obscura.

Commentary

No mention has been made here of the use of a lens in a camera obscura. A lens is placed over the aperture to create a brighter image for the artist to trace. The addition of a lens does not modify the analysis given above.

That said, the lens does augment the quality of the image, giving reflections added highlights and halations. No simple optical explanation accounts for this effect. One does see these same halations in some of Vermeer's paintings. (It is possible that Vermeer saw them in his camera obscura and copied them in his painting.) That said, the evidence for Vermeer's use of a camera obscura is quantitative (the size of the canvases) and not qualitative (halations).


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