Optics and Renaissance ArtCharles M. Falco
11.1 Introduction 266
11.2 Analysis of Paintings 26711.2.1 Jan van Eyck, The Arnolfini Marriage, 1434 26711.2.2 Lorenzo Lotto, Husband and Wife, 15231524 27011.2.3 Hans Holbein the Younger, The French Ambassadors to the English
Court, 1532 27811.2.4 Robert Campin, The Annunciation Triptych (Merode Altarpiece),
11.3 Conclusions 282
11.4 Acknowledgments 283
C.M. Falco (*)College of Optical Sciences, University of Arizona, Tucson, AZ 85721, USAe-mail: firstname.lastname@example.org
The Author(s) 2016M.D. Al-Amri et al. (eds.), Optics in Our Time, DOI 10.1007/978-3-319-31903-2_11
An extensive visual investigation by the artist David Hockney  lead to thediscovery of a variety of optical evidence in paintings as described in a numberof technical papers . This work demonstrated European artists began usingoptical devices as aids for creating their work early in the Renaissance well beforethe time of Galileo. These discoveries show that the incorporation of opticalprojections for producing certain features coincided with the dramatic increasein the realism of depictions at that time. Further, it showed that optics remained animportant tool for artistic purposes continuing until today.
Our earliest evidence of the use of optical projections is in paintings of Jan vanEyck and Robert Campin in Flanders c1425, followed by artist includingBartholome Bermejo in Spain c1474, Hans Holbein in England c1530, andCaravaggio in Italy c1600, to name a few. Significantly, the optical principles ofthe camera obscura were described the eleventh century Arab scientist, philoso-pher, and mathematician, Abu Ali al-Hasan ibn al-Haytham, known in the Westas Alhazen or Alhacen (b.965 Basra d.1039, Cairo). This is important for thepresent discussion because by the early thirteenth century al-Haythams writingson optics had been translated into Latin and incorporated in the manuscripts onoptics of Roger Bacon (c1265), Erasmus Witelo (c1275), and John Peckham(c1280).
Concurrent with the growing theoretical understanding optics were practicaldevelopments, such as the invention of spectacles in Italy around 1276. Pilgrimscarried small convex mirrors into cathedrals to use as wide-angle optics to enable amuch larger area of the scene to be visualized, showing how common the uses ofoptics had become by this time. As described below, evidence within paintingsshows that at some point during this period someone realized replacing the smallopening in a camera obscura with a lens resulted in a projected image that wasboth brighter and sharper. One lens from a pair of reading spectacles allowsprojection of images of the size, brightness, and sharpness necessary to be usefulto artists, although with the optical artifact of having a finite depth of field(DOF). It is important to note that concave mirrors also project images, but withthe advantage for an artist that they maintain the parity of a scene. For this reasonit seems likely that, at least in the initial period, artists used them rather thanrefractive lenses.
The earliest visual depiction of lenses and concave mirrors of which I am awareare in Tomaso da Modenas 1352 paintings of Hugh of Provence and CardinalNicholas of Rouen.1 Either the spectacles or the magnifying glass in thesepaintings would have projected an image useful for an artist. His St. Jeromeand Isnardo of Vicenza both show concave mirrors as well. This shows that thenecessary optics to project images of the size and quality needed by artists wereavailable 75 years before the time of Jan van Eyck.
The examples in what follows are selected from several well-known Europeanartists. As will be shown, in each case features are shown in portions of their worksthat are based on optical projections.
1 These paintings are located in the Chapter House of the Seminario building of the BasilicaSan Nicolo in Treviso, Italy.
266 C.M. Falco
11.2 Analysis of Paintings
11.2.1 Jan van Eyck, The Arnolfini Marriage, 1434
One of the earliest examples we have found of a painting that exhibits a variety ofevidence that the artist-based portions of it on optical projections is shown in. Fig. 11.1. Several different types of optical analysis demonstrate the chandelier,enlarged in . Fig. 11.2, is based on an optical projection.
The advantage of an optical projection of a real chandelier for an artist even ofthe skill of van Eyck is it would have allowed him to mark key points of the image.Even without tracing most of the image this would have enabled him to obtain thelevel of accuracy seen for this complex object that never had been previouslyachieved in any painting. The use of a lens results in an optical base for certain ofthe features, even though a skilled artist would not have needed to trace everydetail in order to produce a work of art even as convincing as this one.
Since an optical projection only would be useful for certain features of anypainting, and not for others, it is important to analyze appropriate aspects of thechandelier to determine whether or not they are based on optical projections. Afterestablishing an optical base it would have been easier for van Eyck to eyeballmany of the features . As a result, paintings like the Arnolfini Marriage arecollages consisting of both optical and non-optical elements, with even the opticalelements containing eyeballed features as well . Another important point is thatall paintings of three-dimensional objects reduce those objects to two dimensionsand, in doing so, lose some of the spatial information.
Elsewhere, based on the size of the candle flame, we estimated the magnifica-tion of the chandelier is 0.16 . This means the outer diameter of the originalchandelier was approximately 1 m which is consistent with the sizes of survivingchandeliers of that period. This magnification is small enough that the DOF for alens falling within any reasonable range of focal lengths and diameters would beover 1 m. Because of this, van Eyck would have seen the entire depth of the realchandelier in the projected image without needing to refocus. Hence, if based onan optical projection the positions of the tops of each of the six candle holdersshould exhibit something close to perfect hexagonal symmetry after correcting forperspective. However, even if he had carefully traced a projected image thereshould be deviations from ideal symmetry due to the imperfections of any suchlarge, hand-made object. If, instead, he had painted this complex object withoutthe aid of a projection, and without the knowledge of analytical perspective thatwas only developed many decades later , larger deviations in the positions ofthese candle holders would be expected.
Marked with dots in . Fig. 11.3 are the positions of the tops of each of thecandle holders. The six-sided shape connecting them is an ideal hexagon that hasbeen corrected for perspective. As can be seen, the agreement of the positions ofthe candle holders with the points of a perfect hexagon is remarkable. Themaximum deviation of any of the candle holders from a perfect hexagon is only7, corresponding to the end of that half-meter-long arm being bent only 6.6 cmaway from its ideal hexagonal position. Importantly, this analysis shows thearms are bent away from their ideal positions, but that none of them is eitherlonger or shorter than the others. This is just what would be expected for a realchandelier. The deviations from perfect hexagonal symmetry are all on a circle,with the root-mean-square deviation only 4.1 cm. Although we shouldnt expect ahand-made fifteenth century chandelier to exhibit accuracy greater than this, someor all of the deviations could have resulted from slight bends during fabrication,transportation, hanging, or subsequent handling.
Chapter 11 Optics and Renaissance Art267 11
. Fig. 11.1 Jan van Eyck, The Arnolfini Marriage, 1434
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Although the overall chandelier is three dimensional, the individual arms aretwo dimensional. We devised an analysis scheme based on this, as shown in. Fig. 11.4 [3, 6]. In this figure we individually corrected each of the six arms ofthe chandelier for perspective and overlaid them to reveal similarities anddifferences. Where a complete arm is not shown in the figure it is because it ispartially obscured by arms in front of it. While the loss of spatial information whenprojecting a three-dimensional object into two dimensions introduces ambiguities,the scheme we used to analyze this chandelier avoids this limitation.
After transformation of the arms to a plan view of each the main arcs areidentical to within 5 % in width and 1.5 % in length. That they are the same lengthis consistent with our independent analysis of the radial positions of the candleholders described above . However, since it would have been easier for van Eyckto eyeball many aspects of this chandelier, rather than to trace the entire projectedimage, it is not surprising that there are variations in the positions of the decorativefeatures attached to those arcs.
From this evidence and other that we published [13, 6] we can conclude witha high degree of confidence that van Eycks chandelier is based on an opticalprojection of a real chandelier. Further, the small differences provide insight intothe artistic choices van Eyck made to deviate from simply tracing the projection.However, the most important point is that the unprecedented realistic perspectiveof this complex object is a result of an optical projection that was made over acentury earlier than previously thought possible .
. Fig. 11.2 Jan van Eyck, The Arnolfini Marriage (detail), 1