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Chapter One

The camera obscura

If a small hole is made in the wall of a darkened room, an image of the sceneoutside can be formed by light rays passing through the hole. The image mayappear on a wall opposite the hole, or can be observed on a sheet of paper orother screen placed in front of the hole. The hole can be in a door, say, or in asolid wooden window shutter. This is the `camera obscura' in its original meaning,the term coming from the astronomer Kepler in the early 17th century.

    Typically the image in this kind of `pinhole' camera obscura is very dim.(`Pinhole' is perhaps misleading. In a room-sized camera the aperture might bethe size of a keyhole.) For the image to be sharp, the hole must be small, andthis of course limits the quantity of light admitted. The outside scene musttherefore be very brightly lit—but even the image of a landscape under theMediterranean summer sun is still faint. A person entering the darkened roommust wait a few minutes for his eyes to adjust, before he can make out thepicture.

    One exception is an image of the sun itself, which is immediately and clearlyvisible. The effect can be seen in attics under ill-fitting tiled roofs, where thesun's rays are focused through chinks between the tiles. The same can happenwhen sunlight penetrates thin canopies of leaves. Aristotle watched an imageof the sun formed beneath a tree becoming crescent-shaped during an eclipse?In this he anticipated the main practical application of the camera obscura upuntil the 17th century, which was for watching solar eclipses withoutdamagingone's eyes.

    The question of how images are formed by light as it passes throughsmall apertures was studied by Chinese philosophers in the 8th century (and

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ing itself must be contained within a `visual pyramid', whose apex is at thisviewpoint. It is possible to determine the positions of the sloping lines thatform the edges of this pyramid. Suppose that these lines are continued back,through the viewpoint, to meet the back wall of the room, behind the painter.They then define a rectangular area on that wall. In at least half a dozen casesthis rectangle is the precise size of the painting in question.

    My explanation for this very curious result is that Vermeer had a cameraobscura with a lens at the painting's viewpoint. He used this arrangement toproject the scene onto the back wall of the room, which thus served as thecamera's screen. He put paper on the wall and traced, perhaps even paintedfrom the projected image. It is because Vermeer traced the images that they arethe same size as the paintings themselves.

    I argue that it is difficult to account for this geometrical phenomenon byreference to other procedures which Vermeer might plausibly or feasibly haveadopted: using conventional mathematical methods to set up the perspectiveviews, for example, or tracing the images reflected in mirrors, as more than onecritic has suggested. By contrast the result is very simply and naturally explicable,once it is supposed that Vermeer was using a camera. The geometricalnature of this argument gives it a special force; if the camera theory is to berejected, a viable alternative explanation still needs to be developed for a mostunusual property of the perspective construction of Vermeer's interiors.

    Lawrence Gowing wrote of the problem of the optical basis of Vermeer'stechnique, `the precise technical solution remains a matter of conjecture. Thetruth is buried? I hope to have disinterred at least part of the truth and in sodoing to have avoided something that Gowing feared: using the pictures `nobetter than as fodder for another of the hobby-horses to which more than onestudy of the painter has been bound.' My purpose has definitely not been tomake `a study of the painter'. In no way is the book intended as a comprehensivetechnical or critical treatment of Vermeer's oeuvre. I have concentrated onjust one aspect of Vermeer's working methods, but one which has an intrinsicfascination in itself and which furthermore concerns the painter's specialgenius for capturing the qualities of light.

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possibly even earlier), and by the great scholar Alhazen writing in Arabic in the10th century. Alhazen's work on optics exerted a powerful influence on someof the most important 13th-century writers on the subject, the English FranciscansRoger Bacon and John Pecham and the Polish philosopher Witelo. Thesethree were in turn to dominate the study of optics by their writings for anothertwo hundred years, until the time of Kepler. For example, in his PerspectivaCommunis (Natural Optics) of 1279, Pecham describes how `When at the time ofan eclipse of the sun, its rays are received in a dark place through a hole of anyshape, it is possible to see the crescent-shape getting smaller as the moon coversthe sun.' By the mid-15th century the use of the darkened-room type of cameraobscura for making solar observations had become standard practice amongastronomers. The first published illustration of a camera (of this or any kind)appears in a book by the Dutch mathematician and astronomer Reinerus GemmaFrisius (Figure 1). It shows an image of the solar eclipse which Gemma Frisiusobserved at Louvain in 1544, projected onto the wall of a classical pavilion.

    For other 16th- and 17th-century authors the camera was merely a curiousdevice for spying on people in the street outside—a trick from the repertoire of`natural magic'. The first hints of possible uses of the camera obscura in artcome in Leonardo da Vinci's notebooks, around the year 1490

An experiment, showing how objects transmit their images or pictures intersecting within the eye in the crystalline humour.

This is shown when the images of illuminated objects penetrate into a very dark chamber by some small round hole. Then you will receive these images on a white paper placed within this dark room rather near to the hole; and you will see all the objects on the paper in their proper forms and colours, but much smaller; and they will be upside down by reason of that very intersection. These images, being transmitted from a place illuminated by the sun, will seem as if actually painted on this paper, which must be extremely thin and looked at from behind. And let the little perforation be made in a very thin plate of iron.

    Leonardo remarks on how the projected image is inverted in relation to theoriginal scene, since the light rays cross as they pass through the pinhole. If acamera image is studied from the direction that the light comes—as in theillustration of Gemma Frisius—then it appears both upside down and reversedleft-to-right (Figure 2a). One further problem here is that the viewer's head canget in the way of the light. To overcome this second difficulty Leonardo proposesa translucent paper screen, viewed from the back. The image as theviewer sees it is still upside down, but it is not now reversed left-to-right(Figure 2b). There is, however, some loss of brightness as the light passesthrough the paper.

    An important technical development in the camera obscura which took placein the middle of the 16th century was the introduction of glass lenses in theplace of simple pinholes. This made it possible to have larger apertures andhence much brighter images, without sacrificing sharpness. As a result itbecame a real practical proposition to use the apparatus for making drawingsfrom life. Convex lenses suitable for the purpose had been widely available forseveral centuries. The first use of spectacles for correcting long-sightedness hasbeen traced to Italy, towards the end of the 13th century. By the 16th centuryspectacles were being produced in quantity and the manufacture of lenses hadbecome an industry.

    There is some doubt about which writer deserves credit for the earliestdescription of a camera with a lens. The honour should possibly go to theMilanese physician and natural philosopher Girolamo Cardano (now bestremembered as a mathematician). The relevant passage from his De Subtilitate(On Subtlety, 1550) runs as follows

If you care to see what goes on in the street when the sun is bright, place in your windows a glass disc and the window having been closed [shuttered] you will see images projected through the aperture onto the wall; but the colours are dull.

    The problem is what does Cardano mean here by `a glass disc' [in the originalLatin: orbis e vitra]? Some historians of photography have concluded that itmust indeed be a lens. But Major-General Waterhouse who compiled a verylearned set of `Notes on the early history of the camera obscura' suggested thatCardano might have been referring to a concave mirror, used to reflect andconcentrate light from the outdoor scene onto the pinhole—somethingdescribed previously by a number of other writers. A lens should certainly notproduce colours that are `dull': `intense' and `jewel-like' are adjectives moreoften used.

    Two unequivocal descriptions of cameras with convex lenses appear verysoon afterwards, the first in a perspective manual published in 1568 by DanieleBarbaro, a Venetian patrician famous for his editions of the Roman architecturalwriter Vitruvius. Barbaro proposes explicitly that the camera be used for producingdrawings in correct perspective. He says that an old man's spectacleglass (i.e. a convex lens) is suitable. He suggests that a diaphragm may beplaced over the lens to restrict the aperture, and so increase the depth of field—althoughthis reduces brightness. He also describes how `Seeing, therefore, onthe paper the outline of things, you can draw with a pencil all the perspectiveand the shading and colouring, according to nature, holding the paper tightlytill you have finished the drawing.'

    A second Venetian author Giovanni Battista Benedetti, writing in 1585, suggesteda method for correcting the inversion of the image, by setting a planemirror at 45 degrees to the direction of the light coming from the lens. This isessentially the arrangement used in most of the portable box-type camerasmanufactured from the late 17th century onwards. These small instrumentswere the forerunners of the photographic camera; indeed they have the samearrangement as the modern reflex camera. Figure 3 shows the principlediagrammatically and Figure 4 shows a 19th-century instrument of this type.The image is projected upwards onto a translucent screen, typically ofground glass—although other translucent materials can also serve. Whenviewed from above, the image appears the correct way up (but still reversedleft-to-right).

    The invention of the camera obscura was at one time attributed to theNeapolitan `professor of secrets' Giovanni Battista della Porta, whose compendiousMagia Naturalis (Natural Magic) became tremendously popular in the16th century and went into more than fifty editions, in several languagesbesides Latin? It was no doubt the popularity of della Porta's book which gaverise to the misconception. He himself did not make such a claim—although hedid imply that he was the first to describe cameras with lenses.

    The first edition of Magia Naturalis was published in Naples in 1558 andincluded a description of a pinhole camera, in terms very similar to Leonardo'saccount. Della Porta greatly expanded his treatment of the camera for a newedition of 1589 to cover the use of lenses and the problem of righting theinverted image. The following extracts are from the 1658 English translation ofthe second edition:

Now I will declare what I ever concealed till now, and thought to conceal continually. If you put a small lenticular [convex] Crystal glass to the hole, you shall presently see all things clearer, the countenances of men walking, the colours, Garments, and all things as if you stood hard by; you shall see them with so much pleasure, that those that see it can never enough admire it.

If you cannot draw a picture of a man or any things else, draw it by this means; If you can but onely make the colours. This is an Art worth learning. Let the Sun beat upon the window, and there about the hole, let therebe Pictures of men, that it may light upon them, but not open the hole. Put a piece of white paper against the hole, and you shall so long sit the men by the light, bringing them neer, or setting them further [i.e. adjusting the focus], until the Sun cast a perfect representation upon the Table [i.e. the drawing board] against it; one that is skill'd in painting, must lay on colours where they are in the Table, and shall describe the manner of the countenance; so the Image being removed, the Picture will remain on the Table, and in the superficies it will be seen as an Image in a Glass [i.e. reversed left-to-right].

As for methods for producing a correctly oriented image, della Portamentions—albeit in slightly vague terms—the use of plane mirrors at anglesand an alternative technique involving convex lenses and concave mirrors incombination.

    Johannes Kepler learned about the camera obscura some time around 1600,from two sources: from reading della Porta and from working with TychoBrahe, who had been using the instrument for making solar observations andmeasurements of the moon. Kepler discusses cameras in both of his works onoptics, Ad Vitellionem Paralipomena (Supplements to Witelo) of 1604, and the Dioptrice(Dioptrics, i.e. the properties of lenses) of 1611. He himself found astronomicalapplications for the camera, as well as other uses, it seems, insurveying.

    Kepler introduced a method for correcting the image in a camera which,rather than involving mirrors, instead used two convex lenses in combination,spaced a suitable distance apart. The principle is shown in the engraving ofFigure 5. This comes from the astronomer Christopher Scheiner's Rosa UrsinasiveSol (The Bear's Rose, otherwise the Sun, 1630) in which Scheiner reports hisobservations of sunspots made using a combination of telescope with cameraobscura—that is, a `projecting telescope'. The upper diagram shows the singlelens camera. The image is upside down [`praesentatio eversa']. The lower diagramshows a camera with two convex lenses—Kepler's arrangement—inwhich the image is now right way up [`praesentatio recta'].

    The English diplomat and man of letters Henry Wotton met Kepler during avisit to Linz in Austria in 1620. Kepler showed Wotton a portable cameraobscura of his own design. It has been suggested that he might have devisedthis instrument for use in the survey of Upper Austria which he was making atthis time. Wotton gives this description in a letter to Francis Bacon:

He hath a little black tent (of what stuff is not much importing) which he can suddenly set up where he will in a field, and it is convertible (like a Wind-mill) to all quarters at pleasure, capable of not much more than one man, as I conceive, and perhaps at no great ease; exactly close and dark, save at one hole, about an inch and a half in the Diameter, to which he applies a long perspective-trunke, with the convex glass fitted to the said hole, and the concave taken out at the other end, which extendeth to about the middle of this erected Tent, through which the visible radiations of all the objects without are intromitted, falling upon a paper, which is accommodated to receive them; and so he traceth them with his Pen in their natural appearance, turning his little Tent round by degrees, till he hath designed the whole aspect of the field: this I have described to your Lordship, because I think there might be good use made of it for Chorography [the making of maps and topographical views]: For otherwise, to make landskips by it were illiberal, though surely no Painter can do them so precisely.

    It is clear from what Wotton says that the basic optics consisted of a modifiedtelescope—the cylindrical `perspective trunk'—with the concave lens removed,leaving a single convex lens. It would have been perfectly feasible for Keplerto have set this tube horizontally and placed the drawing table and paper in avertical position. Wotton's `windmill' comparison and his reference to the easewith which the device was turned hint at another configuration, however—onewhich was frequently used later, in other such cameras designed for landscapedrawing. The drawing table and paper might have been horizontal, and the lenstube placed vertically above this, with a plane mirror angled at 45 degrees abovethe lens to reflect the image of the landscape down the tube. Figure 6 shows thearrangement in diagrammatic form.

    With this arrangement it is sufficient just for the mirror, or a turret housingthe mirror, to be rotated (like the cap of a windmill) in the horizontal plane, andthe view in any chosen direction to be projected down onto the fixed table. Thetent does not have to be turned as a whole. A complete 360 degree panoramacan even be traced, given a sufficiently long strip of paper.

    Figure 7 reproduces an 18th-century engraving by Giovanni FrancescoCosta, in which an artist (at lower left) is using a pyramidal camera of thisgeneral type to make, as it seems, an architectural perspective. Note how heducks his head under the flap of the tent. The turret housing the mirror is at theapex of the pyramid. (It is impossible to tell whether this particular mirrorcould be rotated independently. The alternative would be for the whole tent tobe lifted bodily.) If the user of a camera of this kind faces away from hissubject—as Costa's artist appears to do—and directs the mirror backwardsover his head, then the resulting image matches the real scene: neither invertednor reversed left-to-right (see Figure 6).

    Whether Kepler's tent-type camera was of this design, it is not possible toknow from Wotton's account alone. The arrangement of another portablecamera described by the Jesuit scholar Athanasius Kircher is more certain. Thisis because he includes a drawing of it (Figure 8) in his wide-ranging work onoptics, Ars Magna Lucis et Umbrae (The Great Art of Light and Shadow), publishedin 1646. Despite the apparent scale given by the human figure, the apparatuswas meant to be carried—hence the horizontal poles like those of a sedan chair.J H Hammond, in The Camera Obscura: A Chronicle, suggests that perhaps theentire construction was really intended by Kircher to be much smaller than itseems here, and that the artist was meant to fit only his head and shouldersthrough the square hole in the base. Notice how Kircher's design is for a doublecamera, with lens apertures on two opposite sides. (What might be the utility ofthis remains a mystery. Perhaps it is just a device of the illustrator, to show oneset-up from two different angles.) Each resulting image is projected onto atranslucent screen, on which the artist traces, on the opposite side to the lens.

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Excerpted from Vermeer's Camera by Philip Steadman. Copyright © 2001 by Philip Steadman. Excerpted by permission. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.

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