University of Arizona, and Hockney's studio
 Charles M. Falco and David Graves
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Discussion

This is a discussion between Charles Falco (proponent of optical device hypothesis) and David Stork (criticism). Stork's initial criticism is found elsewhere on this web site, and is quoted briefly here.

Pro-optical

Although David Stork's arguments against our evidence are scattered throughout his fourteen web pages, they reduce to: 1) there is no historical documentation of the existence of appropriate mirrors and lenses during the early Renaissance; 2) artists had sufficient talent that they wouldn't have needed to use lenses anyway; and 3) it would have required an impossible number of candles to provide sufficient illumination to use such lenses. We show that 1) documentation certainly does exist that demonstrates appropriate mirrors and lenses were being produced and used as imaging devices as early as the 13th century; 2) the question of whether or not artists had the talent to paint without the aid of lenses is a logical red herring, unrelated to evaluating the evidence we have presented that, irrespective of their skill level, certain of them indeed did use such lenses; and 3), as we clearly stated in New York, they didn't use candles, they used sunlight.

Response criticism

No. There are several other problems I raised that do not reduce to the above three classes and Falco and Graves do not answer them, for instance Why the embarrassing lack of inverted brushstrokes (even in underpaintings) in Renaissance art? What about alternate explanations? Do they think the first is "unrelated" to the question of whether paintings were at least partially completed upside-down? These problems for the Hockney theory, and others not answered by Falco and Graves, as well as rebuttals to their points will be presented below.

Pro-optical

We have organized what follows according to the headings on the fourteen web pages of Stork's discussion. However, since many of the points Stork emphasizes are unrelated to our evidence for the use of lenses, we have not addressed all of his points that are incorrect or confusing.

Initial criticism

van Eyck

Eyeballing

I've seen many students in the National Gallery and elsewhere copying masterpieces with great fidelity.

Pro-optical

Here Stork invokes an alternative hypothesis ("artistic genius"), which does not address the optical evidence we presented. Unfortunately, as well as not addressing our evidence, his term "great fidelity" is completely subjective, so cannot be tested against any of our optical evidence. The correspondence of a wealth of intricate features on the Albergati drawing and painting are at a scale smaller than 1 mm (0.039"). An optical projection using a simple version of what is now called an epidiascope is the simplest way to achieve such accuracy.

Response criticism

First of all, nowhere do I invoke the phrase "artistic genius," as their quotation marks imply, or even that concept. On the contrary, I refer to "students" and state that there are thousands of paintings done "optically" -- hardly an appeal to "artistic genius." Under my title Talent (not "Genius"), I touted a single individual, a Texas police sketch artist... whom I suspect would be flattered indeed to be associated with the term "artistic genius" that Falco and Graves introduce into the discussion. Even for van Eyck I refer only to his "own patient talent" and summarize the whole discussion thus: "it seems plausible that van Eyck, Leonardo, Caravaggio and other Renaissance painters had the requisite talent." While Falco and Graves here and below may hope to portray my position as somehow relying upon "artistic genius," and thus somehow extraordinary or implausible, the simple fact is that I am not and never have. I don't need to.

Next, it is worth pointing out that neither Hockney nor Falco and Graves themselves had put forth the grid alternative to the optical explanation of the Albergati copy. Why not? Are they that unaware of the history of technology of the time? They ask "How else to account for the convergence except by way of some sort of optical projection?" as if the answer were self-evident. Do they hope their audiences will not bring up alternatives? How can they make claims -- including claims for "proofs"! -- without doing so?

Lorne Campbell, Research Curator at the National Gallery, London, author of Fifteenth-century Netherlandish art and van Eyck expert, claims that van Eyck did the copy by eyeballing (pers. com. 2002). A 1-mm resolution -- the thickness of a dime -- isn't particularly farfetched given that an artist can measure and scale distances (without a grid) and has his own source image in front of him, even if he's enlarging. Regardless, as I wrote, eyeballing is not my favored explanation, but neither can it be dismissed immediately, as Hockney and Falco do. Falco and Graves complain that the eyeballing explanation was not compared to the evidence, ignoring the fact that neither has the optical method.

The epidiascope is by not the simplest means to achieve this accuracy, and has never even been demonstrated in this regard. In the Renaissance it required an expensive and at best rare (but probably nonexistent) device along with strong lighting and complicated setup. A grid construction is simpler and, as I've demonstrated experimentally, gives more than enough accuracy.

Initial criticism

Grid Constructions

Pro-optical

Stork contends our epidiascope explanation fails, and offers "an extremely simple experiment" as proof:

Initial criticism Place a notebook or paperback book on a flat tabletop -- this will represent one of van Eyck's image surfaces (paper or canvas). Now randomly "bump" the notebook." Based on the fact a notebook would rotate when bumped, but there is no relative rotation between the features in the drawing and painting, he concludes the correspondence of details "would be extremely unlikely in the Albergati portraits according to the Hockney/Falco theory.

Pro-optical

Unfortunately, the simple experiment Stork proposes to support his view is an experiment that does not reflect the likely situation of the drawing and the painting both having been mounted on easels of some sort. Obviously, bumping either easel would move it horizontally with respect to the other, but would not result in any rotation whatever between the two.

Response criticism

Falco and Graves are in error here. Earlier I had considered an easel "explanation" but didn't even mention it because it could not account for the data. Because Falco and Graves cannot see this, it pays to show the contradictions inherent in their hypothesis. In short, they ignore my central point which was that, unfortunately for Hockney, Falco and Graves, there are TWO "lucky" bumps -- one horizontal and one vertical. Their new easel hypothesis may ensure that ONE bump is horizontal (and yield no image rotation), but their hypothesis precludes an orthogonal, vertical, bump (and no rotation) -- unless of course they ask us to accept that van Eyck's canvas levitated above an easel rail. (Incidentally, another ad hoc technique of moving the canvas forward and backward would change the magnification and hence cannot explain the vertical "bump.")

Furthermore, Falco and Graves conveniently speak about the rotation but mention neither the ratio of distances of the bumps, which is extremely unlikely in their ad hoc explanation, nor the existence of the lines at the right of the image. And of course their explanation relies at its heart upon complicated technology for which there is no persuasive evidence (see below) while mine relies on simple technology that was used at that period and indeed earlier.

Most importantly, they have stated nothing to cast doubt upon my grid construction and experiment, which remains the best explanation for the van Eyck images and is in every way superior to their optical theory.

Initial criticism

Pantograph

Finally, consider the third method for duplicating the Albergati portrait: pantographs. Leonardo used one.

Pro-optical

Stork is incorrect in his belief that van Eyck could have used a pantograph in 1432. According to Martin Kemp[3], the pantograph was invented by Christopher Scheiner in 1603, over 150 years after van Eyck painted the Albergati portrait, and 84 years after Leonardo's death.

Pro-optical

[3] Martin Kemp, The Science of Art (Yale University Press, 1990). page 180.

Response criticism

This is quite surprising and welcome indeed -- Falco and Graves are sounding like me: claiming that an explanation is invalid because the required device wasn't yet invented. GREAT! They rest their argument on Kemp's book. Did they ever bother to try to look up in that book "epidiascope," or "mirror, concave projection" or anything that would support their projection hypothesis? There is nothing in Kemp's book that gives support to their epidiascope hypothesis in particular or to mirror projection generally. How can they use Kemp's book to discredit pantographs, when in fact it discredits even more firmly their epidiascope hypothesis?

The simple fact is that the pantograph was invented in 1603, long before the Dutch physicist Christian Huygens (1629-1695) invented the precursor to the epidiascope. And if we want to talk about the availability of the components of these devices, the wood sticks of a pantograph were available to cave men tens of thousands of years before the sophisticated concave mirror required for an epidiascope, and the pantograph's parallelogram principle was known twenty-three centuries ago, long before ray tracing in concave mirrors had even been thought of. In short, the pantograph is far more plausible than the mirror projection method, and, as I pointed out, the grid construction is more plausible than either.

In arguing against the pantograph because it hadn't been invented, Falco and Graves are -- unwittingly -- arguing against their theory better than I ever could. Since the long-focal length concave mirror hadn't been invented -- surely not patented -- and there is no evidence that it was used for projections, all their explanations based on it succumb to the dismissal they serve to pantographs. Fortunately for me, I have an alternate explanation, which I clearly and explicitly prefer. Unfortunately for Hockney et al., they don't.

The explanation by grid construction is in every way superior to an explanation resorting to optics. The grid explanation relies on elementary technology known to be used at the time, which in modern re-enactments gives correspondence better than the originals, gives a natural explanation for the direction of BOTH bumps AND their relative distances, and gives a principled explanation for the vertical lines at the right. In contrast, the optics explanation relies on complicated and at best rare devices used in a way for which we have no corroborating textual or representational evidence whatsoever, requiring bright lighting, which has never been verified by re-enactments, can only explain BOTH bumps by appealing to levitation, has no principled explanation for the relative distances of the bumps, and has nothing to say about the vertical lines at the right.

It is no wonder the promoters are not eager to put forth alternatives to their optical theory.

Initial criticism

Lotto

Christopher Tyler has shown that had Lotto followed the steps claimed by Hockney and Falco then the carpet in the scene would have had to have had an asymmetric design for the carpet, as shown here.

Pro-optical

We showed in Figure 6 [Fig. 1] of the 'Optics and Photonics News'[4] manuscript that Lotto shifted his lens when working on the central feature, resulting in two sets of vanishing points that differ considerably from each other. Unfortunately, Tyler's reconstruction of the perspective of this portion of the painting is simply wrong (see our earlier discussion of Tyler's point no. 3). This effect in the image, which Tyler's error has caused both of them to misinterpret as implying an apparent asymmetric design of the original carpet, instead comes directly from Lotto having shifted the position of his lens during production of that portion of the painting. Having had to reposition his lens when producing that portion of the painting is quantitatively consistent with our calculations of the limitations on the imaging properties of a simple lens due to its intrinsic optical aberrations.

Pro-optical

[4] David Hockney and Charles M. Falco, Optics and Photonics News 11, 52 (2000)

Initial criticism

Caravaggio

Caravaggio figures prominently in Hockney's theory, yet this painting exposes numerous awkward implications of the theory related to refocusing, moving the canvas, and illumination.

Pro-optical

Stork's incorrect inference of three "awkward implications" for "Supper at Emmaus" comes from his misunderstanding of what is proposed. An experiment based on this very painting was carried out in Hockney's studio in May 2001. The results of that experiment, in which Hockney used a refractive lens to assemble the painting as a collage of separate elements according to the theory, were entirely consistent with what the theory suggests for refocusing, moving the canvas, and illumination.

Response criticism

As I stated in my piece, "I am aware of just three modern demonstrations" and describe them; of course I cannot comment upon experiments that have, to my knowledge, not been revealed to the public. We look forward to Mr. Hockney presenting his May 2001 results in sufficient detail and clarity in a scholarly forum so that others can judge them, including issues such as the consistency of viewpoints, direction of brushstrokes, color fidelity, and much more. Until Hockney reveals this evidence I'm afraid we'll have to withhold judgment on their claim that the results "were entirely consistent" with their theory. Regardless, knowledge of simple optics ensures us that if Hockney had refocused on Peter's right hand as he describes in his book, then he would have moved the both the lens and the canvas six feet, an awkward and unlikely step.

Initial criticism If Caravaggio had employed the methods of Hockney and Falco, how many candles would he have needed?

Pro-optical

We answered this at the New York symposium, and the answer is the same now: none. As we each stated then, direct sunlight is the likely source of illumination, since direct sunlight has the necessary brightness.

Initial criticism there are numerous Renaissance paintings done by artificial light, such as George de la Tour's evocative scenes...

Response criticism

One throws up one's hands in exasperation! When I quote Mr. Hockney, the originator and driving force of the theory and the titular reason for the symposium, when he wrote that Caravaggio "...worked in dark rooms -- cellars -- very common in those days... He used artificial lighting" and his supporters respond instead "direct sunlight is the likely source of illumination" one doesn't know whether the proponents realize their blatant contradiction, or that they think we won't see it, or what. At the very least, Falco and Graves should take Mr. Hockney aside and tell him to stop misleading the popular press. To wit: one august periodical known for penetrating research and trenchant skeptical analysis, when interviewing and lavishing praise upon Mr. Hockney and his bold theory, states that Caravaggio "[w]orked in darkened cellars -- which you need for the lens to work. Strong artificial lighting (ditto)" [1].

Regardless of such contradictions on this central matter of illumination, their argument against the historical record of Caravaggio's estate (which contained no concave mirror but several candle holders), his working methods that included at least at some periods a dark cellar without sunlight, and so on -- reviewed over centuries by art historians -- seems to be that it is incompatible with their new theory. Caravaggio's biographer G. P. Bellori wrote in 1672: "He never showed any of his figures in open daylight, but instead found a way to place them in the darkness of a closed room, placing a lamp high so that the light would fall straight down..." Joachim von Sandrart wrote in 1675: "He used dark vaults or other shadowed rooms with one small light (liecht) above, so that the light falling on the model made strong shadows in the darkness..." The unjustified claim that Caravaggio used optics forces the proponents into the extremely awkward conclusion that he worked under bright sunlight.

Pro-optical

Stork's literal interpretation of the contents of paintings is very odd indeed. There is no reason whatever to assume scenes were illuminated by the sources of artificial light depicted within those scenes, just as there is no reason to assume scenes containing dragons were painted with dragons actually present.

Response criticism

It's not odd at all that a painter would best paint what he sees, or arrange his studio to appear close to how he wants his final painting. Not odd at all, especially in the Renaissance. It is very odd indeed that a painter would try to make a painting look like it is night time when in fact the scene is illuminated by bright sunlight, or would work with very dim inverted images much of which are out of focus, or would use an extremely rare (and probably nonexistent) technology when he had done other methods, or had to constantly correct for color (see below) -- all as arising in the Hockney/Falco theory. Now THAT is passing odd! Hockney and Graves write: "There is no reason whatever to assume scenes were illuminated by the sources of artificial light depicted within those scenes" but in fact there is, and every representational artist I know (save possibly Mr. Hockney) would have chosen artificial illumination had they wanted to produce the painting de la Tour gives us. If de la Tour wanted to show light passing through the translucent fingers of the girl, to show the proper shadows of the man's left thumb and the wooden beam's left corner, to get the highlight on St. Joseph's forehead, he would use the candle. Even the slight irregularities, if any, can be explained by slight repositioning the models during the execution and does not require two exposures of sunlight. Arranging such "exposures" would be extremely awkward, where bright sunlight comes from the left for one figure, then must somehow come from the right for the other, all to make the light appear as if it emanated from a point at the candle! Mr. Hockney's suggestion that this painting was done by sunlight is extremely implausible.

I think it pays to pause for a moment, particularly for the artists reading these pieces who may be a bit bewildered by technical talk of focal lengths and so on, to rely on your eyes for a moment. I invite you to expand the de la Tour painting, study it carefully for several minutes, all the time saying to yourself "Hockney and Falco claim this painting was made with the models illuminated by bright sunlight" as described on page 128 of Secret Knowledge. For a few minutes, rely on your own visual intelligence and see if you agree.

[1] "Have you seen the new David Hockney?" by Andrew Marr, pp. 44-50, High Life (October, 2001) [British Airways inflight magazine]

Initial criticism Optics

Pro-optical

No comment is necessary on this section.

Response criticism

I'm glad it is now clear to Falco and indeed everyone that my criticisms both at the symposium and on this website of the Arnolfini mirror have always been on its focal length and thus the size of the sphere from which it was cut (according to Mr. Hockney) -- not the areal size of the mirror face itself.

Pro-optical

Focal Lengths


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