Vermeer and the Camera Obscura: Part II

"Rediscovery"

Joseph Pennell In 1891, before eyes had been accustomed to the modern photographic camera's way of seeing, Joseph Pennell, an American lithographer and etcher, was the first to suppose that Vermeer employed an optical device for painting.^{Joseph Pennell, "Photography as Hindrance and a Help to Art," Journal Camera Club 5 (1891): 75.} Pennell noted the conspicuous discrepancy in scale of the two figures in Vermeer's Officer and Laughing Girl (fig. 1). Even though the officer is seated very close to the girl, he appears disproportionately large on the picture plane, although the perspective is mathematically correct. In fact, the officer's head is about twice as wide as that of the smiling girl. Today, we are quite familiar today with foreground objects appearing very large in snapshots but in seventeenth-century painting this is rather unusual.

Despite the painter's close distance from the scene, as in the case of the Officer and Laughing Girl, there is an instinctive tendency to compensate for the difference in size and render what he knows rather than what he sees.^{For centuries painters had both a working and theoretical knowledge of perspective and understood very well that, to create a believable three dimensional space, figures which appeared far from the viewer had to be represented smaller while those which were nearer had to be proportionately larger.} An example of this compensation can be seen a work by one of Vermeer's contemporaries, Gerrit van Honthorst (The Procuress ). In Honthorst's picture the figures are placed in an almost identical positions as those in Vermeer's work but they appear almost the same size on the picture plane (fig. 2).

In 1946, A. Hyatt Mayor, a curator of the New York Metropolitan Museum, spoke not only of distortion in size of near objects, but of color and tonality of Vermeer's painting which seemed to be "blended as perfectly as the ground glass of a camera" and of the highlights on foreground objects which "break up into dots like globules of halation swimming on a ground glass."^{A. Hyatt Mayor, "The Photographic Eye," Metropolitan Museum of Art Bulletin (Summer 1947): 15–26.}

In 1950, Lawrence Gowing,^{Lawrence Gowing, Vermeer (London: Faber and Faber, 1952).} noting Vermeer's indifference to linear convention and extreme economy in modeling, wrote, "The technical part of it is plain. It is likely Vermeer made use of the camera obscura." Gowing suggested Vermeer could have acquired the necessary technical knowledge in optics from his fellow citizen in Delft, Antonie van Leeuwenhoek, who in addition to his fame as a designer, grinder and user of lenses, is also recorded as the executor of Vermeer's estate. Nonetheless, the most pressing point for Gowing was not question whether or not he painted with the camera obscura or learned from it, but why he chose the "optical way" to begin with? Most of Gowing's text focuses on answering the question in stylistic and psychological terms. In any case, Gowing thought that the technical question was destined to produce little more than "fodder for another of the hobby-horses to which more than one study of the painter has been bound."

On the other hand, the Dutch scholar P. T. A. Swillens, who had meticulously investigated Vermeer painting methods and geometrically reconstructed the rooms represented in his paintings, steadfastly refused to see why Vermeer would have had the need to use any sort of optical aid, be it a mirror, a camera lucida or a camera obscura.^{P.T.A. Swillens, Johannes Vermeer: Painter of Delft (Utrecht: Vitgeverij het Spectrum, 1950).}

Charles Seymour was the first to test in real life circumstances the hypothesis that Vermeer was guided by the images he saw in a camera obscura. ^{Charles Seymour, "Dark Chamber in a Light Filled Room," Art Bulletin 46 (1964).} Seymour observed similar objects—he carefully chose Vermeer-like props—in similar lighting conditions to the ones found in Vermeer's painting through a real nineteenth-century camera obscura and found that the resulting image exhibited qualities much like those seen in Vermeer's paintings.

In particular, the lion head finials of a mock Spanish chair appeared, in his opinion, surprisingly similar to the one seen in the Girl with a Red Hat. Just as those of Vermeer's image, the pin-point specular highlights glimmer with the so called disks (circles) of confusion, or pointillés as they are traditionally called when they are translated into paint. Pointillés, a conspicuous feature of many of Vermeer's paintings, cannot be perceived with the naked eye and do not seem likely stylistic invention. They are, however, produced by the camera obscura's imperfect lens. Seymour also found that the fuzzy rendering of the tapestries in Vermeer's Lacemaker and Girl with a Red Hat recall parts of the satin drapery used in his experiment. Seymour's investigation was primarily limited to only two paintings by Vermeer, the Girl with a Red Hat and the Girl with a Flute.

Seymour termed his work "preliminary" and suggested that "more research would be profitable, in particular regarding the relationships in the seventeenth century between such experimental milieu as Rome and Paris and England and Holland."

In 1971, Daniel Fink once again built a real camera obscura in order to investigate the matter.^{Daniel A. Fink, "Vermeer's Use of the Camera Obscura: A Comparative Study," The Art Bulletin 53, no. 4 (Dec. 1971): 493–505.} He set it up on a table, pointed it at objects that were similar to those in Vermeer's paintings and found that there were, in his words, "remarkable similarities" between the artist's paintings and the camera's image. His experiments were conducted in a laboratory similar to a room used by Vermeer, which provided northern light (preferred by painters for centuries). Fink maintained that there were characteristic signs of the camera obscura in 26 paintings by Vermeer, the great part of the artist's oeuvre.

Fink found ten points which link the visual qualities produced by the camera obscura image and those of Vermeer's paintings:

1. Variations principal planes of focus;
2. precise diminution of circles of confusion;
3. halation of highlights;
4. precise treatment of reflections;
5. closeness of the point of view to the window wall;
6. precise convergence of parallel lines located in a plane
   perpendicular to the viewing axis;
7. use of curtains to darken viewing room and control subject
   illumination;
8. relative detail in still life portion versus figure detail;
9. consistent proportions of the paintings (4–5:5 or almost
   square);
10. dimensional precision in rendering objects.

Although Fink "hoped that an undiscriminating search will not be initiated which looks for optical phenomena under every suspicious circular blob of paint" he concluded that "Vermeer was unique in his employment of the camera obscura because he left for us the evidence of his use of the instrument in his paintings. Not only was the camera obscura useful in helping Vermeer to render what he saw with the unaided eye, but it also provided significant enrichment of the subjects which he did not fail to include in his finished paintings."

In 1998, Allan A. Mills ^{Alan A. Mills, "Vermeer and the Camera Obscura: Some Practical Considerations," Leonardo 31, no. 3 (1998): 213–218.} came to the conclusion that "it would not have been possible for Vermeer to have painted his interior scenes directly, at full size, from images produced by a room-type camera obscura incorporating the lenses of his time. Such images would have been much too dim and in any case would have been mirror images of the real scene." However, Mills did not rule out that the painter "could have observed and even been stimulated to sketch the more brightly illuminated images produced at a smaller scale by a portable camera obscura." Mills explains that the extreme accuracy of Vermeer's perspectives, one of the strong points of the pro-camera obscura argument, "would not have necessitated a camera." He could have produced them by using graphical methods taught by his fellow countrymen Hans Vredeman de Vries (1527–c. 1607)  and Henricus Hondius (1597–1651) in conjunction with a well-known technique which made use of a pin inserted at the vanishing point with a thread attached to it and held taut to define the orthogonals of the scene.

While the theoretical debate as to whether Vermeer used a camera obscura or not made no substantial progress, the issue polarized Vermeer scholars in opposing camps. Those favorable read into Vermeer's use of the device signs that he was in tune with the spirit of his time when the study of optics held an important place in nascent scientific investigation. The opposing camp argued, essentially, that by definition great artists have superlative skills and have no need for mechanical devices, or that the characteristics of the camera reveled in Vermeer's paintings may be explained by prevailing painterly styles. Moreover, the characteristics of the machine’s image hadn’t seemed to make much sense to his contemporaries seeing that only one Dutch painter (Gabriel Metsu) ever replicated them, and almost certainly in response to Vermeer. Believers argued that naysayer art historians dreaded the use of mechanical device, because it would diminish the stature of the artist's as a creator and, perhaps, a bit of the prestige of the art historians themselves, key negotiators between the artist and the public. Practicing painters generally brush aside the matter maintaining that the use of a technological device is nothing for an artist to be ashamed of: it is another tool, like brushes, paint or canvas, rather than a substitute for artistic talent.

Philip Steadman & the tracing debate

In 2002, after years in preparation, the London architect Philip Steadman published his influential Vermeer's Camera: Uncovering the Truth behind the Masterpieces, a detailed study of Vermeer and the camera obscura notable for the author's level-headed deduction and intellectual clarity.^{Philip Steadman, Vermeer's Camera: Uncovering the Truth Behind the Masterpieces (Oxford: Oxford University Press, 2001), 21.} Beginning with measurements of the original maps and the known dimensions of period floor tiles in Vermeer's paintings, Steadman was able to establish scale and precisely correlate the images Vermeer's of paintings and the concrete measurable world they represent. He concluded that not only the dimensions of the rooms shown in Vermeer's interiors are very similar, but that at least a dozen of Vermeer's best-known pictures are set in one and the same room.

But more remarkably, the London architect provided evidence that the artist may have projected the camera's image on a sheet of paper on the back wall the device in order to trace the principal outlines of his compositions, which could be then transferred to the canvas.

Working from measurements of the original maps prominently featured in Vermeer’s interiors, Steadman was able to correlate the images of Vermeer’s scenes to the concrete, measurable world they represent in true scale. Other means of fixing the absolute scale were provided by the musical instruments, known paintings on the background walls and by the small Delftware tiles that skirt the perimeters of the floor, which were manufactured to standard sizes. Steadman concluded not only that the dimensions of the rooms represented in Vermeer’s interiors are very similar, but that at least ten of his best-known pictures are set in one and the same room. For each of these ten paintings Steadman found—through a process called reverse geometry—that it was "possible to determine the theoretical perspective viewpoint: that point within the room at which Vermeer would have had to put his eye to see the precise view in question. The entire extent of this view—everything that is visible in the painting—is contained within a ‘visual pyramid’ whose apex is at the viewpoint (fig. 3). If the lines forming the edges of this pyramid are carried back to meet the back wall of the room, they define a rectangle on that wall. For at least six paintings this rectangle is the size of Vermeer’s canvas." Paul Taylor, of the Warburg Institute, and Tim Gowers, a Rouse-Ball Professor of Mathematics at Cambridge, calculated on reasonable assumptions that the odds that such coincidences as random occurrences are hundreds or even thousands-to-one against. Steadman advanced that the most plausible conclusion is that in these six works Vermeer used a lens to project the image on the background and traced its main contours. He calculated that the focal length of the lens used by Vermeer can be estimated from the distances between lens and projected image, and between lens and subject, using the standard formula, which would be something around 75 cm.

Following the publication of Vermeer’s Camera, a number of art scholars have cast caution to the wind and embraced Steadman’s theory—it bolstered a number of their own hypothesizes wherein Vermeer is characterized as a natural philosopher. Doubters see Vermeer's imitation of certain characteristics of the machine's image—discs of confusion, variety of focus and contraction of tonal values—as a stylistic novelties which, after all, hadn't seemed to make much sense to his contemporaries seeing that no one else replicated them. After all, had the camera obscura been a useful tool for painting, it is extraordinarily simple to construct and operate, provided one might possess a suitable lens.

Today, approximately half of the world's leading Vermeer specialists believe the artist used the device in the manner advanced by Steadman.

Walter Liedtke, perhaps the art historian most critical of Steadman’s theory, wrote that "whether he [Vermeer] first saw something in the environment, an optical device, or another painter’s work is a complicated question precisely because once seen the effect became part of the artist’s repertoire, a characteristic of his style to be repeated or modified at will. That much was learning. The rest of it—genius—cannot be explained."^{Walter Liedtke, Vermeer: The Complete Paintings (Ludion, 2012).} In effect, Liedtke did not oppose completely the notion that Vermeer responded in some way to the camera obscura, but, rather, the drastic devaluation of the role of artistic creativity in the realization of the artist's finely constructed works. What Liedtke found in Vermeer's oeuvre is an "overwhelming evidence of pure invention" including the fact that rooms like those seen here never existed in Delft. He also noted that in the extensive inventory of Vermeer's estate or in any other house in Delft (according to John Montias' survey of several hundred inventories), there is no mention of any drawing device by the two distinguished diarists who visited Vermeer.

Arthur K. Wheelock Jr., who originally embraced the camera obscura/Vermeer tie, has backtracked and now holds that Vermeer "must have admired certain effects of color, light and focus in a camera obscura, but that he persistently departed from what he actually saw in the camera, in his studio, or in another artist's work in accord with his own highly refined aesthetic and expressive goals." Martin Kemp views Vermeer’s characteristic pointillés as a form of painterly shorthand which, although optical in origin, are artificially contrived in application.^{Martin Kemp, The Science of Art: Optical Themes in Western Art from Brunelleschi to Seurat (New Haven: Yale University Press, 1992).} Mariët Westermann goes so far as to suggest Vermeer "played up the signs" of a camera obscura because of their "very modernity."^{Mariët Westerman, "After Iconography and Iconoclasm: Current Research in Netherlandish Art, 1566–1700," The Art Bulletin 84 (2002): 351–372.}

Those inclined to see these trademark characteristics not as a stylistic embellishments but the most tangible sign of a much profounder interest in optics have made the case that the artist was nothing less than a natural scientist equipped with paint and brush: an optical illuminist whose name can be mentioned along side those of René Descartes (1596–1650), Galileo Galilei (1564–1642) and Plato. Robert D. Huerta points out that the conceptual and methodological links between the Delft painter Vermeer and his near neighbor and exact contemporary, the microscopist Antony van Leeuwenhoek, broadening his study to consider the connections between painting and science during the seventeenth century.^{Robert Huerta, Giants of Delft. Johannes Vermeer and the Natural Philosophers: The Parallel Search for Knowledge during the Age of Discovery (Lewisburg: Bucknell Univ Pr, 2003).} Huerta argues that Vermeer's use of the camera obscura parallels Van Leeuwenhoek's pursuit of the "optical way," and embodies a profound philosophical connection between these investigators

The Vermeer/camera obscura issue also fed into what to the mainstream art community consider a highly sponsored "conspiracy theory," advanced by English Pop artist David Hockney and physicist Charles Falco. In an opulent coffee-table book,^{David Hockney, Rediscovering the Lost Techniques of the Old Masters (London: Thames and Hudson Ltd, 1994).} the authors proclaimed to have discovered proof that many of the world’s greatest masters secretly employed mechanical devices to make progress in realism. The Hockey-Falco theory received a great amount of public attention, soothing the anxiety of average museum goers who are baffled by the works of the old masters. It also played well to the press—the "mystery" of the old masters had finally been resolved. Hockney’s proofs, however, have been pushed back by counter-studies and discounted by most specialists, most notably the scientist and author David Stork, some of whose rebuttals are published in the Art & Optics website.

The seventeenth century left not a single reference to Vermeer’s involvement with an optical device, or to what is now referred to as the "optical" or "impersonal" register of his works, which isolates his production from the picturesque traditions of Dutch genre painting. Although this sort of "visual neutrality" provokes something akin to ecstasy among Vermeer advocates today, it may have struck contemporary viewers differently, perhaps as a stylistic quirk; a trick rather than a truth. In fact, thirteen years after Vermeer’s death, the Dutchman G. T.s’Gravensande wrote that the effect of the camera obscura "is striking, but false." While it is true that the supreme Dutch art connoisseur Constantijn Huygens was impressed by the image of the camera and commended it wholeheartedly to painters, it is likewise true that aside from Vermeer, and perhaps Jan van der Heyden (1637–1712; fig. 4) and the obscure painter Torrentius (Jan van der Beeck, 1589–1644), Dutch painters happily ignored the miraculous machine and went about approximating the look of nature by traditional means just as they had done for decades. Whatever its cause, the "photographic" effect of Vermeer’s work that we so admire today may have struck common Dutch citizens as too dry or too distant from their personal experience of nature, which, given the geographical and meteorological peculiarities of their homeland, must have been intensely physical, and not only optical.

For those who wish to investigate this fascinating topic beyond these web pages, the resources listed on page four of this article should provide a wide range of facts and interpretations

Evidence of the camera obscura in Vermeer’s painting

For an artist who took such obvious delight in rendering light, shade, color and how patterned surfaces react under different conditions of light, the optical charms of the camera's image must have been notable. Since the camera obscura leaves not physical trace when it is used, specialists submit that there exist essentially five aesthetic features in Vermeer’s paintings that demonstrate his familiarity with the device: precision in perspective, precision in drawing, precision in tonal rendering, compositional refinement as well as pointillés and variations in focus. The remaining virtues of Vermeer’s art, such as cleanliness of design, a reduced number of figures and props, the unaffected poses of his models, positive color harmony and a deliberate ambiguity of narrative, can be explained by artistic choice and, naturally, by a peculiar temperament that lead him to pursue certain aspects of pictorial representation that his colleagues deemed only marginally interesting.

Perspectival Accuracy. Steadman is certain that not only did Vermeer use the camera obscura to study visual phenomena and formulate his compositions: he believes that he traced its projection on a piece of paper attached to the back of a camera obscura automatically resolving critical problems related to perspective. Although the perspective geometry of the camera’s image will be exactly the same as that of a conventional linear perspective drawing or a normal photograph, distortions around the periphery of a camera obscura image are noticeable. However, it is likely that in most cases such distortions can be manually corrected, especially if we take into account that those objects near the edges of the picture that might necessitate the use of linear perspective to reveal themselves correctly (i.e., floor tiles or window panes) do not generally have complicated shapes and can be easily extrapolated from those areas which can have been determined with certainty. Alternatively, the artist may choose to crop the distorted areas from the composition of his picture or, more simply, plan the composition so that its salient features fit within the area where distortion does not occur.

The patterns of the floor tiles and the window structures in Vermeer’s interiors demonstrate an exceptional level of perspective accuracy (fig. 5), although the smaller ceramic-tiled floors of the early two shoe-box interiors show minor flaws. These inaccuracies, however, may be more related to the difficulties of hand painting such tiny tiles, especially those located in the background,which are small and very distorted, rather than errors in projection. Despite De Hooch’s best efforts it is possible to find that the floor pattern to one side of a figure in his interiors that do not properly align with the pattern of tiles on the other side of the figure.^{David Hockney, Rediscovering the Lost Techniques of the Old Masters (London: Thames and Hudson Ltd, 1994).} This anomaly never occurs in Vermeer’s work.

Precision in Drawing. Even to the untrained eye Vermeer’s drawing seems very precise. His versions of the maps are so accurate, down to every last cartouche and little sailing ship on the ocean that in several cases—as James Welu has shown—it has been possible to identify not just the map’s designers and publishers, but the specific editions. Analogously, not only can the open book that lays in front of the gazing scientist in The Astronomer be recognized; the very page at which it is open can be determined (fig. 6).^{James A. Welu, "Vermeer's Astronomer: Observations on an Open Book," Art Bulletin 68 (1986).} But even if such objects look highly detailed, are they also correct from a mathematical point of view?

By measuring extant objects found in museums that are identical to those that appear in Vermeer’s paintings, Steadman was able to deduce the absolute sizes of other objects in the pictures. He found that the perspective reconstructions of two types of chairs are within one or two centimeters of the museum originals. Even more surprising, not only are the topographical features and decorative elements of the maps precisely represented detail-to-detail and in relative positioning; equally important, the overall dimensions of each map corresponds closely to the originals, within only a few per cent of the surviving library copies. Such accuracy is difficult to imagine without the aid of some sort of mechanical (the drawing frame) or optical device. One has only to look at the interior scenes of otherwise supremely skilled Frans van Mieris (1635–1681), Gerrit er Borch (1617–1681) and Gerrit Dou (1613–1675; fig. 7) to note that while their ability to draw single objects may be indeed astounding, objects do not always appear to relate to one another properly in perspectival space, as if the they had been developed independently.

Critics of Steadman’s hypothesis argued that in some cases, such as the picture-within-a-picture of Moses represented in dramatically different dimensions in two different compositions (fig.8 & 9) the artist took significant liberties in drawing. Steadman, however, replied that while it is evident that Vermeer availed himself of poetic license in many cases, this fact does not negate the extraordinary accuracy in the others. According to Steadman, from a practical point of view, there are no great technical difficulties in making simple outline drawings using the camera: all that is needed, he maintains, is "patience, a steady hand, and the ability to make a series of decisions as to where significant changes of tone and color should be marked by lines."

Precision in Tonal Value. Of all Vermeer’s technical accomplishments, his command of tonal value remains, perhaps, the most proverbial, but, understandably, the most perplexing for the layman. Without correct tonal values, light and form cannot be adequately described, and the distance between objects can be only gauged by the use of geometrical perspective and overlap. However, due to the visual system, discriminating between tonal values for the scope of creating highly representational images is very difficult. The abstract artist and art teacher Josef Albers (1888–1976) wrote, "very few are able to distinguish higher and lower light intensity (i.e., higher and lower value) between different hues …only a minority can distinguish the lighter from the darker within close intervals when obscured by contrasting hues or by different color intensities."^{Joseph Albers, Interaction of Color (Yale University Press; Anniversary edition, June 28, 2013).} The well-known diagram (fig. 10) by Edward H. Adelson (Professor of Vision Science at MIT) demonstrates how dramatically difficult it is for the eye to judge absolute tonal values. The squares A and B on the illusion have the exact same tonal value, and yet they seem to be intrinsically different owing to their context.

But what exactly is tone? Due to the vagaries of the English language, tone is often a misunderstood word, particularly when used by artists and art historians. Tone, sometimes referred to as "value" by painters, simply refers to how light or dark, or how bright, a color appears to be. To judge tone one must temporarily ignore texture, shape, detail and color as if looking at a black and white photograph without regard to subject matter. Tonal values, then, are distinguishable gradations of brightness between white and black. In optimal conditions the human observer is able to perceive around 1,000 different shades of gray over the entire luminance range, while the number is lower in an average viewing environment. Most humans need a 1% change in brightness to discriminate one gray from another. A painter does not need to render all the perceptible values to convey form and light. By narrowing the intermediate tones of his pictures, the sense of light and form can be evoked with great power.

The perception of tonal value is very complex because the biological function of sight aims uniquely at assuring the instantaneous recognizably of solid objects and understanding their location in space. This goal is achieved through a number of mechanisms referred to as perceptual constancies, also called object constancy, or constancy phenomenon. Perceptual constancies enable us to see objects as having standard shape, size, color or location regardless of changes in the angle of perspective, distance, or lighting condition: the perception tends to conform to the object as it is assumed to be, rather than to the actual stimulus, which in nature may vary enormously. For example, we see a distant bus down the road, which is objectively may occupy a minuscule part of the overall field of vision, as having the same size as another bus which has just arrived at the bus stop a few meters away (size constancy). A handkerchief in a deep shadow looks white even though it objectively reflects the same amount of light as a piece of coal exposed to the direct rays of the sun (brightness constancy) and snow appears white in the low illumination of moonlight, as well as in sunlight 800,000 times as bright. This is because the our visual system does not measure light in absolute terms like a light meter. It compares the amount of light from the coal and from the paper to the average amount of light from the surrounding environment. In order to create illusionist images, the painter must learn how to undo perceptual constancies, particularly brightness constancy, perhaps his most vexing enemy.

Tone is influenced by the tones that immediately surround it, oftentimes dramatically so. For example, a patch of light gray on a pure white field looks much darker than the same gray on a pure dark field when they are displayed in close proximity (fig. 11). Even when the observer becomes conscious that both grays have the same value, he is unable to "see" them as equal no matter how hard he tries. Even for trained artists, tonal value is difficult to isolate from color, although it is clear that certain painters possess a superior sense of tone, such as the Spaniard Diego Velázquez (1599–1660) and the American John Singer Sargent (1856–1925). Painters once used a small mirror, slightly convex in shape, with its surface tinted a dark color, called the "Claude glass" (fig. 12) in honor of the landscape painter Claude Lorrain (c. 1600–1682), to reduce the impact of color and narrow the tonal range of natural light. Another widely practiced trick to evaluate tone is to study the scene with squinted eyes. Squinting diminishes the intensity of color and narrows the range of natural brightness bringing them closer to the tones available to the painter. In any case, although some musicians possess what is termed absolute, or perfect, pitch, the rare ability of a person to identify or re-create a given musical note without the benefit of a reference tone, even the most gifted painter cannot identify absolute tonal values with such precision.

Steadman, who was certainly not the first to praise what is universally believed to be Vermeer's exceptional sense of tone, holds that the camera would have greatly aided the artist's quest for the greatest tonal veracity. While there exists no manner that allows tone and color to be mechanically "copied" directly from the camera's screen, simple observation confirms that the camera compresses the hopelessly wide range of natural brightness to a narrow range much closer to that of the artist's pigments, producing an image that lies somewhere between reality and a printed photograph. While the highlights of shiny objects and areas of a scene inundated with bright light will still be much brighter than the most brilliant white paints, the image of the camera offers an intermediate stage in the process.^{Philip Steadman, Vermeer’s Camera: Uncovering the Truth Behind the Masterpieces (Oxford: Oxford University Press, 2002).} No less important, the tones of the projected image are circumscribed within a very small surface area so that adjacent tones can be judged more accurately. In effect, the trained painter is almost able to "see" on the camera's screen the colors he will need to mix on his palette.

Compositional Refinement. Although there can be no doubt that Vermeer possessed an extraordinary sense of pictorial design unique in the history of Western art, Steadman maintains the camera would have helped the artist to perform compositional experiments and craft an optimal layout adapted for each theme. Apart from offering interesting optical effects, the camera instantaneously collapses reality onto a single plane, evidencing two-dimensional relationships that are less apparent in naked-eye observation. In theory, this would diminish the need to make time-consuming drawings in order to evaluate compositional efficacy. Although there is no historical documentation in seventeenth-century literature that refers to the camera obscura as a compositional aid, it is not out of the question that Vermeer employed the device for this purpose. The painter Carsten Wirth, who conducted experiments with the device in real studio circumstances, speculated that Vermeer no longer designed the actual scene according only to the narrative of the painting and traditional compositional criteria; "the camera changes not only the appearance of the motif, but…the motif itself."^{Carsten Wirth, "The Camera Obscura as a Model of a New Concept of Mimesis in Seventeenth-Century Painting. Inside the Camera Obscura–Optics and Art under the Spell of the Projected Image," Max Planck Institute for the History of Science, 2007, 152.}

Some writers have suggested that the unusual cropping effects produced on the screen of the camera may have inspired Vermeer to truncate parts of his scenes, for example, the left-hand arm of The Guitar Player. But painters of the Utrecht Caravaggists, whose works Vermeer was very familiar, routinely cropped their figures to increase the sense of physical immediacy, an effect which Vermeer evidently pursued in the London piece.

Focus. Another argument that has been marshaled to demonstrate that Vermeer used the camera obscura is the perceived variations in focus found in some of his pictures. The camera obscura produces, among other optical aberrations, an image where some areas are in focus and others are not, because in spite of their relatively good quality, a single lens cannot focus the image through the entire field of depth of a scenes such as those of Vermeer located relatively near the lens. This means, for example, that if Vermeer brought the head of the young girl of The Lacemaker into focus, the still life in front of her would appear blurred. And this is the way Vermeer rendered the scene, at least to a certain point. Another example of the play with focus is relatively evident in The Art of Painting. The hanging cloth foreground still life has the curious, fuzzy quality that reminds the modern viewer of nothing more than a poorly focused snapshot. However, anyone who has experience with a real, single-lens camera obscura knows that the difference in focus is far more accentuated than it ever appears in Vermeer’s painting (except, perhaps, for The Lacemaker).

Although critics have occasionally attempted to demonstrate that Vermeer portrayed the variations in focus of the camera obscura systematically, there are many instances which demonstrate that, instead, he mediated selectively between what he saw with his naked eye and what he saw through the camera’s lens. Returning to The Lacemaker, for example, the figure, which stations in the picture’s middle ground, is in discreet focus. Instead, the red and white threads issuing from the sewing cushion closer to the viewer appear greatly unfocused, as one might expect had the image been transcribed faithfully from the camera obscura. However, on the very front of leaf-patterned carpet, the most advanced plane of depth of the picture, it is possible to make out a single, meandering blue thread which is perfectly sharp, as thin as a real thread (fig. 13). The fact that this lone thread is in sharp focus even though it is much closer to the viewer than the red and white threads demonstrates that Vermeer either refocused his camera during the working process or, more simply, ignored some of the information the device for the sake of an aesthetic or poetic advantage.

Pointillés. In certain circumstances of natural lighting, the effects of the polished mirror and imperfect focus of the camera obscura inspired one of the most distinctive features of Vermeer’s paintings: the so-called pointillés. When used in reference to Vermeer's painting, a pointillés is a pictorial approximation of a natural pin-point highlight that is not brought exactly into focus at the camera’s viewing plane, making it spread out into a shimmering circle. In photography, these are called "halations" or "discs of confusion." In a camera obscura, discs of confusion usually occur only when strong light shines upon polished materials such as silk, glass and metal. They cannot be observed on opaque materials or in shadows. Today, Vermeer’s pointillés probably appear much less striking than in his own day because we have grown used to the quirks and peculiarities of a wide range of mechanically produced images, some of which are now purposely replicated as an aesthetic compliment in both traditional and computer-generated graphics. Of all the stylistic features in Vermeer’s paintings linked to the camera obscura, only pointillés are universally accepted.

Pointillés, which appear in roughly half of Vermeer's paintings, make their debut in his early Girl Reading a Letter by an Open Window, and are liberally scattered through the works that follow. Their most dramatic presences are in View of Delft, The Milkmaid (fig. 14) and The Lacemaker. However, many pointillés in Vermeer’s pictures, perhaps the overwhelming majority, would have not occurred on the camera obscura screen, such as those along on the bottom side of the shadowed hulls of the boats in View of Delft. In the late Allegory of Faith pointillés (fig. 15), which swarm over the hanging tapestry, have clearly evolved into an independent stylistic device, severed from their optical origin.

Although Vermeer may have chosen to reproduce, rather than repress, a defect of the camera obscura, very probably pointillés would not have been understood outside the small circle of cognoscenti and art collectors familiar with the workings of the device. To a contemporary seventeenth-century laymen Vermeer’s pointillés might have made no more sense than a stylistic quirk. In fact, even though today Vermeer’s pointillés are considered among the most distinguishing and attractive features of his manner, they were replicated by only one of the (few) painters who emulated his work, and in single painting.^{Gabriel Metsu, Woman Reading a Letter, c. 1664–1666, Oil on wood, 52.2 x 40.2 cm., National Gallery of Ireland, Dublin.} In his own time, highlights were invariably painted with dashing flecks of light paint, which, however, were never so deliberately circular as Vermeer's. Nonetheless, Walter Liedtke pointed out that the presence of certain optical effects such as pointillés "in no way implies that the artist who produced them must have used a camera obscura" pointing out the similarity in treatment between the highlights of a lion-head finial chair done by Vermeer (fig. 16) and another done by Frans Hals (fig. 17), who painting has never been associated with optical instruments.^{Walter Liedtke, Vermeer: The Complete Paintings (Ludion, 2012), 182.}