We have photography
When François Arago announced the photographic process developed by Daguerre in the famous session of August 10, 1839 the success was immediate. Everyone was amazed at the fine details that the technique could render. It was as if the limit were the sight itself, as if the image printed on polished silver held much more riches than could be discerned with the naked eye. However, despite the great enthusiasm, the people directly involved with the new process knew that it still had one point that urgently needed improvement. This weak point was the optics that the first cameras used.
The lens used was an achromatic doublet manufactured by the best French optician, Charles Chevalier, but his optical design seemed to be at the limit of what it could yield and no one could imagine anything that could be done differently and make it better. The specific and most pressing problem is that the lens was extremely slow, that is, it produced a dark image and demanded something like thirty minutes of exposure even on a sunny day. Practically impossible to use with any moving subject. This frustration was immediately felt by the nascent photographic community which, in fact, existed even before the invention of photography. For photography was long expected and discussed among scientists, artists, dilettantes, and people of the optical and equipment industry. At least since Wedgwood experiments in the late 18th century there was already a feeling that sooner or later the chemical process to fix camera obscura images would be found. But the lens problem became clear and evident only when the daguerreotype established a reference on the necessary exposure. Only then people realized that there was no optic for photography. The solution was Petzval’s lens.
Far better than human vision
The problem to solve in the construction of a photographic lens is not an easy one. It has to be comparatively much better than our own vision. This may seem strange, but it is enough to note that our gaze is more like a scan than an instant record of a complete scene, as is the case with photography. Our vision is only really good and records details in a small portion of our retina. Out of this small circle that corresponds to a very modest angle of vision, what we “perceive” is something very indefinite and gives us only a sense of what we have in our visual field outside this small center. It is for this reason that when we enter a new environment, crossing a door, for example, our eyes must “walk” through the whole scene if we want to make a recognition of what is there.
In the case of the photographic lens, it needs to record everything accurately in a single shot because with the photograph ready, printed on paper or screen, we want to be able to look and do the same type of scan that we would do if we were before the real scene. It is in this sense that we require from a photographic lens more our own eyes can deliver.
Lenses used in direct vision, such as telescopes or opera glasses, two types of application that were common at the time of the invention of photography, follow the same logic of sweeping vision and only a small angle of the visual field interests us. For this reason, although lenses were known from antiquity, until the nineteenth century, it had never been demanded of a lens what it needs to provide when used for photographic recording. In his book The Optics of Photography and the Photographic Lens, J.Trail Taylor puts the question in the following terms: “In photographic optics the construction of the lens must be such as to give a sharp image of the object to which it is directed, but also of which lie within certain extent on either side of the center.”
Once understood the problem, let us go through the hurdles that hindered its immediate solution.
The process of lens making is still today basically done with grinding and polishing. It starts with an optical glass, cut or moulded to be as close as possible to the final shape, then it is ground and finally polished. This shape was invariably a spherical one on both sides, that is, a surface with a fixed radius of curvature. It could be concave or convex, but the surface was always spherical. This was a constructive limitation and at the same time a virtue since the polishing process allowed to start with an iron cap, coarsely adjusted, to end with a practically perfect spherical surface and precisely determined radius of curvature. This happens because the polishing transfers to the polished object not the local form, of each point of the model (as would be the case of casting in a mold) but the average of all its points. This can give a very fine precision. Only at the end of the 20th century did non-spherical lenses begin to be commercially produced, but the entire photographic optics developed from combinations of spherical surfaces with air/glass, glass/air or glass/glass passages.
What happens in these passages is that the light ray changes direction. Phenomenon known as refraction. Usually demonstrated with prisms, which are flat, but is obviously the basic principle also in spherical lenses. Refraction is known and reasonably described even before the formulation of any wave theory of light. The first treatise on optics that already contained some elements that would still be valid today, among them something about refraction, was an Arab, Ibn Al Haithan (965–1039) who lived in Cairo City, Egypt (La Lumière – Bernard Maitte). As for the word lens, it comes from Latin and refers to lentil (legume). In French it has even the same lentille spelling that refer also to lenses. Corrective lenses for vision are known since Antiquity, but it was with Galileo’s improved telescope that optics took a definite impulse to become what would become during the industrial revolution and to this day.
The first problem that had to be solved when more quality of the lenses’ images was demanded was the question of chromatic aberration. As it is easily observed with prisms, different colors undergo different refractions from different angles and so the first telescopes presented uncomfortable colored fringes around the objects, perceived mainly if seen against a dark background. But in 1723 the Englishman Chester Moore Hall (1703 – 1771) “demonstrated that it is possible to construct achromatic combinations by joining polished lenses of different suitably chosen glasses” (La Lumière – Bernard Maitte). The good idea was to use a converging lens along with another divergent lens made of another glass, so that the set still retained the convergent character, but in such a way that the second lens generated an inverse chromatic aberration that practically annulled the aberration. This second lens had a different dispersion power .
It was with this type of lens, the achromatic doublet, that photography was discovered. But chromatism was only the first battle. Other problems awaited those who did not just want to see better and also wanted to record what they saw.
A camera can be thought of as just a dark box in which light is admitted on one side and the image projected on the opposite side. It is intuitively obvious that the brightness of the image will depend on how much light is let in, ie the size of the hole in camera front. Hole in which the lens is placed to tame the light, that is, to make the light that has diverged from the objects converge to form a clear image (if this is strange for you to visit this page). With the limitation that the surface of the lens was necessarily spherical, the opticians found the following problem:
Even with the chromatic aberration dominated, when they tried to increase the lens to increase the light input and make the image brighter, it was noticed that the light rays did not converge properly on the image. Those passing near the axis converged at a greater distance than those passing through the most peripheral part of the lens. The effect is due to the surface of the lens being spherical and therefore it was given to this problem the name of spherical aberration. The result is the loss of sharpness in the image because small circles are produced from points in the object. In the central region of the image this effect can still be tolerated because it is not so pronounced, but the situation becomes very serious with light beams oblique to the axis of the lens.
Introduction of the diaphragm to correct the spherical aberration
In Fig. 47. (Monckhoven) above, if we assume the approximation that the beam of light coming out of point B, on the axis of the lens, converges satisfactorily on F, we observe that the light coming from point A, when passing through the upper part of the lens (marked in blue) converges at a much shorter distance than the light emitted by the same point A passing through the lower part (green beam). Considering that the green part, although it is not ideally converging on the same plane in which F is, it is converging to a distance much closer to the plane of F as compared to the blue beam. The solution was to cut the portion that most badly damaged the image.
So the remedy found to improve image quality, sacrificing its luminosity, was to interpose between the scene and the lens a diaphragm D, as shown in Fig.48. With this device, generally a metal plate with a circular hole and later the adjustable iris, the not so bad part of the light is selected to try to approach the image in a flat field. Yet, the surface that would receive the sharpest image is a concave surface marked by the red line. This phenomenon by which spherical lenses form curved images is called the curvature of lens’s focal surface or field curvature. It is often found in the literature, regarding lenses that have a good correction for this problem, the qualification that they have a flat field. The lenses for which the corrected spherical aberration is considered (it is always an approximation since there is no possible total correction) are called aplanatics (aplanétiques in French). The Petzval lens was the first aplanatic lens – a necessity brought about by the invention of photography.
The Petzval solution
The spherical aberration produced by a converging lens is conventionally said to be positive. The focus of the beams passing the periphery of the lens are closer to the lens than the focus of the beams passing through the center of the lens (Fig 47 and 48). We say that the field curvature is outward (red line in Figure 48 above). It is concave from a stance inside the camera. In the case of a divergent lens what happens is the inverse, that is, the focus of what arrives passing through the periphery of the lens gets farther and the beams passing through the center will focus at a shorter distance. It is said of the divergent lens that it has a spherical negative aberration and that the field curvature is inward. It is convex when seen from a stance inside the camera.
Just as the chromatic aberration was corrected satisfactorily with the use of a divergent lens in conjunction with the convergent lens, in such a way that the effect of one was annulled by the other, but always keeping a convergent effect for the whole (to form an image on the film ), the spherical aberration with curved outward field, was also solved by Petzval by the addition of a lens with inverse effect, i.e., curved inward field.
It would be good if a single divergent lens could do both jobs. But in optics care must be taken with these terms as heavy as canceling, annihilating, correcting … because everything is actually done by approximations. The aberrations are not in fact zeroed, they are simply pushed to a plateau within the resolution acceptable to the image in its largest possible portion. In this sense, a single doublet, a single divergent/convergent pair, can and usually are thought to improve a little of the two things: chromatism and field curvature; but a second achromatic doublet with reverse curvature gives much more options for the optician to work and deal with the two aberrations, with more degrees of freedom and therefore greater efficiency. That was Petzval’s choice. He started from a landscape lens, an achromatic doublet, and added a second, air-spaced doublet that would bend the field in the opposite direction, generate a negative spherical aberration, and thereby obtain a “flat field”. It inaugurated thus, as was said above, the era of aplanatic lenses.
The front element, facing the scene, is the cemented doublet on the right in the above illustration. It is almost flat/convex but its back surface is still slightly concave and thus forms a convex/concave lens whose name is meniscus. The rear element has two functions. The first has already been described, it is a matter of straightening the focal plane by bending it “inwards” since the first doublet curves it “outwards”. The second function was also of paramount importance and refers to the luminosity of the lens.
The brightness of a lens depends on its useful area, it is called the entrance pupil, which is nothing more than the apparent size of the diaphragm (apparent, as it may actually appear and work as if it were larger than it really is, see a full description about it here) and also depends on the focal length of the lens.
The higher the pupil the brighter the lens will be. The higher the focal length the less brighter the lens will be. Well, the addition of Petzval’s rear doublet shortened the focal length of his lens. When the light passes through a second convergent doublet it will obviously converge at a smaller distance than passing only through the first. With such a shorter focal length the lens has also become more luminous without having to increase the useful diameter of the lens which, as we have seen, accentuates the problem of spherical aberration.
The Petzval’ portrait lens
The lens projected by Petzval had an aperture f/3.6 (Eder page 292). This is a very good aperture even by today’s standards. It is true that sensitive materials have evolved enormously and this has alleviate pressure on the optical industry to produce brighter lenses. But the fact is that openings much larger than this are not very feasible. Some 50mm lenses for 35mm film photography have apertures of f / 1.2 and up to f / .95 (Canon, for example) but what happens is that the lens starts to be sized comparable to the film or sensor itself, image quality drops and are still too expensive to manufacture. This is unthinkable in large format, for example, where lens diameter would be enormous. The conclusion is that we can say that Petzval arrived at his first attempt at something close to the limit of the reasonable in terms of luminosity. It is more rewarding investing on the side of the sensitive material and keep the lenses at this level of aperture as they have historically been.
The lenses available prior to Petzval’s innovation were, as was said above, simple achromatic doublets, in barrel, with a diaphragm in front of them. The maximum one could open that diaphragm and maintain a minimum image quality was f/15. The consequent exposure time fell in the range of tens of minutes. The portrayed had to stand still all this time in the sun if they wanted to have their figure registered for posterity.
In the first attempts with the new lens it was possible to make a portrait in 1 ¼ minutes with the original process of the daguerreotype. When chemical accelerators using bromine and/or chlorine vapors were added to the process as early as 1840, that time dropped to something like 15 to 30 seconds. (Eder, p. 293).
But the sharpness of Petzval’s lens, strictly speaking, was still just enough to make a good portrait. Outside a central region where the second doublet still provided a flattening of the field curvature, the image rapidly deteriorated. We read in the Traité d’optique photographique comprenant the description of objectifs et appareils d’agrandissement de Désiré von Monckhoven (1834-1882), written in 1866: “The double objective [thus was referred to Petzval’s objective by differentiating the simple objective, or of landscapes or even French, which had only one doublet] is intended for portraits because it is the fastest of all the optical combinations invented so far. It has a very large diaphragm (f/5 or f/6) [ here, Monckhoven surely refers to the ones more readily available and not specifically to Petzval’s prototype which had f/3.6] it clearly covers a small extension of the focal plane (f ÷ 3) but with a smaller diaphragm, f / 10 for example, the extension of the sharp image grows a lot and reaches from f÷2 to 2×f÷ 3. Finally, with a f/20 diaphragm, the image extension becomes equal to f. “
So let’s see what that means. A Petzval double lens with 150 mm focal length, aperture f/5 or f/6 will produce a sharp area of f/3 ie 150 ÷ 3 = 50 mm, a 50 mm diameter circle.
The photo on the carte de visite above measures 60 x 85 mm. I have no indication that it was produced with a Petzval or even its date. But it serves to give us an idea of the proportions of what was considered a portrait, for it is certainly within a very common aesthetic and format standard at the beginning of photography. The marked circle is 50 mm in diameter and matches the sharpness area of a 150 mm lens that would be close to its 1/8 plate size. The entire plate was 18 x 24 cm and sometimes quoted as 16 x 22 cm (as in Lerebours et Secretan catalogues).
It is important to note that people did not appreciate what was produced outside the area of sharpness, and the photographer often masked the picture, leaving only the well-focused part on view. The photo above is an example of this. The irony is that today the blurred background seems to marvel more than the portrayed person. We’ll talk about this later.
Petzval’s lens history
It is very interesting the way Josef Petzval got involved with photography. Interesting as well is how in 1862, after his famous lens for portraits and intense activity, when he developed other lenses, published new theories and discovered new laws of optics, he completely abandoned everything that related to the study or application of lenses. His trajectory is very illustrative of the relationship between science and technology in the formation of modern society. To our contemporary view, it may seem that science and technology have always gone hand in hand, but the truth is that for many centuries they ignored each other. The great names of the scientific revolution in the seventeenth century, such as René Descartes (1596-1650) and later Isaac Newton (1642-1726/27), were in no way motivated by the concern that their theories would or should have any practical application. At the other end, manufactures were still organized in guilds or other associations of medieval inspiration. They lived far from the universities and conveyed the secrets of their specialties through the tradition of the master and apprentice. They did not imagine that by studying mathematics or Natural Philosophy (name then given to Physics) they could develop new techniques and improve their productivity. Even the concept of “improving productivity” by itself, would already seem strange to preindustrial thinking. The story of Petzval’s lens is a case that illustrates well what was at stake in the new relationship between industry and academia when science and technology finally met.
Josef Maximilian Petzval was born in 1807 in Hungary into a German family. His father was a middle school teacher. Josef graduated in engineering and became a professor of mathematics at the University of Budapest. In 1835 he was called to teach advanced mathematics at the University of Vienna, where he also entered the Academy of Sciences. It was not by chance that there was a great cultural and business effervescence in the city, for it was the emperor’s policy to foster this environment, and especially his chancellor Klemens von Metternich (1773-1859) was an enthusiast of new technologies. So much so, that when he learned of the novelty of the daguerreotype, he sent to Paris Andreas Freiherr von Ettingshausen (1796 – 1878), professor of mathematics and physics at the university, to get acquainted in detail about the new invention and to be there at its official presentation at the Academy of Sciences in Paris. The way he learned about the novelty is also interesting. It is said that Daguerre himself, better in public relations than in chemistry or optics, sent Emperor Ferdinand I, as a gift, two photographs of his authorship.
There was an internationally renowned optician in Vienna, Simon Plössl, who was educated at the Voigtländer house, another major optical instrument manufacturer, also based in Vienna and who would have a key role in this story as we will see next. It was Plössl who soon built a daguerreotype camera with a Chevalier type lens, but with improved rays that he himself calculated. He used both optical glasses manufactured by the Waldstein family that produced crown and flint (two types of glass used in Chevalier’s doublet) of excellent quality. The Waldstein were also settled in Vienna. Ettingshausen, had discussed Daguerre’s invention with the director of the university and he appointed a young physics assistant, Anton Georg Martin, to learn and master the photographic process. He would be the first to test Petzval’s lens later.
Most of these people met regularly at the atelier of a painter, who was also a physicist and naturalist, named Carl Schuh. They even had a name: the Furstenhof Circle (D’Agostini), borrowed from the neighborhood where the atelier was located, and discussed as many subjects as the diversity of attendees could encompass. They were artists, scientists, entrepreneurs and dilettantes; people from inside and outside the academic world. Regarding the group’s opinion about the novelty of Paris, Eder (p.290) sums it up as follows:
“The small aperture of Chevalier’s lenses with which Daguerre equipped his camera was generally deplored. Professor Ettingshausen recognized at once, when daguerreotypy was first made public, the insufficiency of the ordinary Chevalier lens, which was exported from Paris all over the world. As a colleague and friend he was acquainted with Petzval’s genius for mathematics and optics and induced him to make a closer study of the problems involved in the construction of better photographic lenses, to which Petzval responded enthusiastically.”
On the theoretical side, laws of refraction that govern the behavior of light passing from one medium to another, such as air and glass, and which would thus serve to understand its path through a lens, were studied by Snell and published by Descartes in his Dioptrique as early as 1637. So two hundred years before the invention of photography. A complete formulation of the wave theory of light was made by Christiaan Huygens (1629-1695) in 1678, of which Descartes was preceptor. On the practical side, the achromatic doublets were invented by Chester Moore Hall, for use in telescopes, around 1730, but he did not made public his discovery. The Englishman John Dollond also developed his achromatic doublet to equip telescopes and made it known in 1758. All this was done, Eder notes (p. 251) through experimental methods, successive tests without a systematic effort of understanding the physics that was behind the phenomenon observed. Later, the German Joseph Ritter von Fraunhofer (1787-1826) in Munich, at the beginning of the nineteenth century, showed the exact calculation for the understanding of achromatic lenses and brought together physical theory and lens manufacturing technology. He took over a hybrid role linking academy and industry.
Despite this reservoir of scientific theoretical knowledge and the involvement of physicists such as Fraunhofer in practical matters such as the making of glasses and lenses, optical instrument manufacturers still saw little use for mathematics to improve their production. Rudolf Kingslake, in his A History of the Photographic Lens, reports that Charles Chevalier was aware of his lens’s deficiency in terms of luminosity, but Kingslake says that the maximum Chevalier could do was try out and combine several doublets from his shelf to see if with some of the pairs taken practically at random would get a better result.
The mathematician Josef Petzval marks the transition. The collaboration between academia and industry, in the case of optics, originated from a very peculiar situation. Modern science owes much of its birth to sky’s observation. It was in the astronomy of Kepler and Galileo that the Earth began to revolve around the Sun and not the other way around. This fact, apparently unrelated to the daily life of the inhabitants of our planet, had a devastating effect on the medieval conception that the world, created by God in his infinite wisdom, would be an eternal mystery to mankind. They thus inaugurated a mechanistic conception of the universe as a great clock, a conception which, without denying a divine origin, opened the way for human understanding through systematic investigation, of the scientific method, in the founding molds of Descartes.
Historically, the collaboration between craftsmen and scientists had never put the two in very close relation. Science before the Renaissance was more philosophical, reflection work and little manual activity, little laboratory, few equipments. Exception to this was just astronomy with its wonderful astrolabes and observatories developed above all in the Arab world. But these were basically instruments of measurement. They demanded precision, exhibited technical and aesthetic excellence, but if they served science, they did not use science for their construction beyond their measurements and specifications. They demanded no more than a technique of casting, finishing and engraving.
When optical instruments such as telescopes and microscopes became part of the scientific arsenal, craftsmanship was still needed, as scientists in general would not even know how to melt and shape metal or glass. Craftsmen went a long way in designing lenses experimentally but there came a point where geometrical optics with consideration of the laws of refraction became absolutely necessary. With the photographic lens the trial and error method proved to be definitely fruitless. By comparison, although the steam engine was invented without the use of thermodynamics’ laws, lenses for use in astronomy, capable of rendering quality images would be unlikely, lenses for photography, impossible, without the collaboration of manual and intellectual work between technicians and scientists.
Analyzing from this angle, the case of Petzval lens was the product of his individual talent but also of a community and a policy that had been developing in Vienna for some decades. The model came precisely from Munich where Fraunhofer worked both in basic research, developing the wave theory of light, observing the solar spectrum, as well as guiding and providing designs and specifications for applications in the optical instruments industry and production of optical glasses. As already said above, it was Fraunhofer who finally equated the achromatic lenses and published his results, later assimilated by lens manufacturers. Munich was at the time the most important center for optical development in Europe. From Vienna, at the university, two teachers worked in close collaboration with Fraunhofer. They were Johann Joseph von Prechtl (1778 – 1854) and Simon Ritter von Stampfer (1792 – 1864). Eder wrote that during Fraunhofer’s life the two were limited to sharing more academic subjects. They avoided establishing an open competition between the two centers. But after Fraunhofer’s death, the university’s assistance to the opticians in Vienna, where the Voigtländer and Plössl family were established, for example, was a kind of patronage with no other purpose than the joint development of science, technology, and market. Even at the installation of the optical glass industry, Prechtl played a key role, assisting and strategically guiding the production of crown and flint glasses in Vienna.
On this role of tutors, Eder comments further that “the young Wilhelm Friedrich Voigtänder owed his technical education to Stampfer, presumably in the early thirties [19th century].” Very important, he studied under his guidance the processes for determining refractive indices in prisms “. When Petzval began his research to improve Charles Chevalier’s lens, the physicist Ettingshausen advised him to look after Friedrich Voigtänder and find information on the refractive indexes and dispersion of glasses commercially available.
The university had assumed as part of its role to form and provide scientific knowledge for technical application in industry, and did so without the latter becoming obliged to any compensation. That was seen as a public service aiming at regional development. Other sectors with non-financial interests also contributed to the new lens project. It is reported that a certain Archduke Ludwig, general director of artillery in the Austrian army, requested by Petzval, ordered that two officers and eight gunners, trained in ballistics, to help him to mathematically simulate the path of light rays to theoretically evaluate the behavior of the lens they were developing. This very tedious numerical work would now be executed by computers in milliseconds. To Petzval and his team it took six months, at the end of which they returned in May 1840 with a proposal for the lens for portraits, which was described above, and a second lens for landscapes in which they sacrificed light a little in exchange for a larger angle of view and a flatter field. This lens would later be known by the name Orthoscope. Name that refers to the orthogonality that offered to subjects mainly of architecture.
It may have helped this climate of disinterested patriotic collaborations that the optical industry, prior to photography, had as its main assets in producing telescopes and microscopes, items that we could well assume were largely returned to the scientific community, or at least for professional and limited use. In that sense, scholars were helping those who provided them with their tools. With photography the scenery changed. The product has become popular, massive, and has handled very large sums of money. That quickly soured the short honeymoon between scientists and lens makers in Vienna.
The cooperation between Petzval and Voigtänder
The Voigtänder family had been established in Vienna since 1756. Initially dedicated to fine mechanics, but already from the second generation ownwards, when Johann Christoph Voigtländer took over the business in 1815, he included in his portfolio optical instruments. Johan had been trained in lenses in England. When Petzval calculated his lens in 1840, the third generation commanded the now very prestigious company in the hands of Peter Wilhelm Friedrich von Voigtländer (1812-1878). Peter was also a frequenter of the Furstenhof Circle and knew Petzval. As we saw above, Peter collaborated in providing the indices of refraction and dispersion that Petzval needed for his project. It was to him that the latter confided in secret the detailed drawings and specifications of his first lens.
Voigtländer then produced the long-awaited lens. It had a focal length of 150 mm and a conical-shaped all-metal camera in which the daguerreotype had a circular shape. Focusing and framing were done on a ground glass and then the entire camera was removed from the stand and taken to a darkroom for replacement of the ground glass by the sensitized metal sheet. Back to the stand, the photograph was taken. About seventy of these cameras were manufactured according to Kingslake (p.37) in 1841 and six hundred in 1842. But only 3 complete sets are known today. Extremely rare are also the daguerreotypes made with it. There was an edition of official replicas made by the Voigtländer firm itself, long afterwards, and even these are very much disputed and true museum pieces, like the above specimen at the Nicéphore Niépce museum in Chalons sur Saône in France.
Voigtländer did not hesitate to immediately include the new lens among its products and the commercial success was enormous and instantaneous. Petzval had not made any kind of contract stipulating any participation or rights of exploitation in quantities, time or other terms about his design. He simply gave all the specifications so that his friend optician would carry out his project. Voigtländer, took the gift as simply another case in a row of contributions he had received from the university since the days of Stampfer and others. In order to show his appreciation for Petzval, to whom it is said that he had the highest esteem, he gave him 2000 guilders as gratification. As an order of magnitude, that would be like the price of a very expensive lens or three or four normal lenses. Until the early 1950s, therefore in something like ten years, Voigtländer manufactured and sold eight thousand lenses.
Petzval saw a great injustice in this appropriation, which he thought was undue, of his creation. The relationship between the two was strained and in 1845 Petzval wanted nothing more with Voigtländer. At that time, he still used the firm’s workshops for experiments and assistance in carrying out new optical projects, but even on that he gave up. He seemed to be so frustrated about the cooperation that he began, without assistants and with his own hands, to grind and polish his own lenses. Eder reports that he was even very efficient in this home production and sold several lenses, but only privately. He did not start it as a new business. (p.297).
As for Peter Friedrich Voigtländer, one must take some care and do not rush to list him in the stereotype of the smart entrepreneur taking advantage of the naive scientist. If so, he would probably have taken some basic care and planned the launch of the new lens. He would have protected rights for Voigtländer firm, patented the designs in his favor, would have sold licenses to other manufacturers in other countries, among other obvious measures quite known to his time. But it seems that he too was taken by surprise and treated the new lens as it probably treated the scientific instruments he used to make and that certainly had a much lower demand.
Instead, the invention that had no protection whatsoever for either its inventor or the manufacturer was right away publicized. For already in 1841 the portrait lens was sent for competing for an award offered by the Society of Encouragement of Paris. The idea was to award a significantly better alternative to lenses currently available for photography. To Petzval’s lens it was given a second place, a flagrant jury’s assessment error that rewarded a new lens of Charles Chevalier that had a much inferior performance. What came next was that the lens of Chevalier was abandoned and that of Petzval copied by all the manufacturers who wanted so, and there were many.
Eder (p. 296) laments the tendentious stance of Potonniée, a French historian, who in his Histoire de la Découverte de la Photographie attributes the success of Petzval’s lens to the fact that French people are fond of foreign products and value what is more expensive only by thinking that price indicates the quality. In fact, German lenses costed on average twice as much as a French lens. But Potonniée does not mention the fact that the French ones were copies of the Germans and never made any reference to their true inventor, Joseph Petzval. In the catalogs of these manufacturers, as in Lerebours et Secretan of 1853 reproduced below, the objective was referred to as “double objective”, “objective of combined glasses”, “German objective” or “German system”.
In any case, Petzval’s lens remained the best lens for portraits for many decades. Towards the end of 19th century, with the development of new glasses and anastigmatic lenses, when photography was about pursuing a practically perfect image without distortion or loss of sharpness, other lenses made history. But even today, perhaps we can even say: especially today, a portrait made with a Petzval design reveals a very seductive beauty.
Joseph Petzval leaves optics
Recalling, in May 1840, Petzval and his gunners had produced two drawings that were given to Peter Friedrich Voigtländer. One was the lens for portraits and the other a lens for landscapes. Perhaps eclipsed by the instant success of the first, this second lens was archived, forgotten in Voigtländer’s drawer, and was not released to the market.
After breaking with Voigtländer in 1845, as we have seen, Petzval continued to study theory, developing and even making other lenses alone. In 1856, when the wet plate process, invented by Frederick Scott Archer (1813 – 1857) in 1851, was clearly the future of photography, as it allowed much larger images on glass plates and much shorter exposure times than the Daguerreotype, Petzval was asked by the The Imperial Military Geographic Institute of Vienna, as well as the Government Printing Office, to develop a new lens to use the new process. Petzval saw an opportunity there to introduce his landscape lens drawn in 184o.
This time he teamed with another optician called Dietzler and launched a review of the first drawing. They came to apply for and received an Austrian patent for the new lens they called Photographischer Dialyt. It was launched in 1857, and was very well received for photographs mainly of architecture and reproduction of works of art and documents. The advantage is that, although more stoped down than the portrait lens, it had a wider viewing angle and presented little distortion to the standards of the time.
This movement caught the attention of Peter Friedrich Voigtländer and he recognized the lens design which in his view belonged to him. He recovered the specifications and released the same Orthoscope lens in 1858 from his factory in Braunschweig to where he had changed his production, leaving Vienna, as a protective measure regarding patent problems. Petzval reacted and there was a lawsuit to settle the issue. Eder reports that in the course of the dispute it was clear that Petzval had really forgotten that he had also given this drawing, almost twenty years ago, to his presently enemy. Peter Friedrich Voigtländer joined in the process the original drawings and a prototype he had made in 1840 and won the dispute.
Due to the power and prestige of the Voigtländer name, and also the characteristics of the lens, the Orthoscope has quickly become a success and practically synonymous with the new category of landscape lenses. Dietzler and Petzval were forced to abandon the name they had given to the lens, Dialyt, and began selling their production also under the name Orthoscope. They enjoyed a relative success and in the exhibition of 1862, in London, they received, along with Voigtländer, medals for their Orthoscope lens. But Petzval seemed really an unlucky man for business. Dietzler was very weak in managing the firm and despite the good start, shortly after the medal on the show, a number of problems drove him to bankruptcy.
Deeply frustrated and depressed with all the wear and tear in his disputes with Voigtländer and now with this new failure in the undertaking that should be his rehabilitation, Petzval decided to abandon completely everything that had relation with lenses or optics in general. Not even classes and lectures at the university he wanted to keep. From then on he devoted himself to acoustics. As a scientist he was very respected and enjoyed prestige and admiration from his colleagues and authorities. He died in 1891.
Using a Petzval lens today
The lenses for portraits with Petzval’s design still arouse much interest among photographers and public. This would not happen, were it not for the fact that the images look indeed very beautiful. Another point that I believe to contribute is that we are a bit scared about where technological progress has brought us and then flirting with such old technologies offers us a compensatory effect, or an illusion of independence from the present in building our future.
As we have seen above, the field curvature is well corrected in the center of the image, something like f÷3 when fully open, and outside this circle the spherical aberration takes over and generates an interesting blur that, according to the subject, appears as a kind of whirlpool. Importantly, this effect is very different from loss of focus by depth of field, due to a very open diaphragm in modern lenses. Depth of field is inherent to any lens, old and new. The spherical aberration, which for oblique rays is called the coma, is something that today can be well corrected or even dosed according to the preferences of the optician who designed the lens. Some soft focus lenses offer a dial that subtracts correction according to photographers’ will.
To use a Petzval lens today photographers have two basic options:
- Shoot with film or some historical analogue process, in large format; using lenses actually made in the nineteenth century(I don’t think Petzval lenses are made for large format in these days. It would be more expensive and less charming than old Petzvals).
- Acquire one of the new versions that are manufactured today for digital, full-frame or APS-C format.
In the first option, buying the lens is not so obvious, depending from where you live. However it is possible to find them on international online and offline auctions and trade shows such as Bièvres. The price varies greatly according to the manufacturer and mainly size of the lens. Many lenses do not bear any brand, they are like generic Petzvals. If they have a focal length between 150 and 250 mm, to make 1/8 to 1/2 plate, that would be 6 x 9 to 13 x 18 cm, it will cost, in good condition, something like 250 to 500 euros. Lenses from Voigtländer, Jamin-Darlot, Lerebours et Secretan, will cost 2 to 3 times this price. There are Petzval type lenses with smaller focal lengths but they are hard to find items. In general they equipped stereo cameras or are lenses designed for projection. The larger lenses, for full plate or super-large-format cameras, are seldom offered and quickly purchased for a few thousand euros.
If the objective is to explore the aberrations and their contrast with the well-defined center, one can acquire a lens designed for a smaller format and use it in a larger format. For example, a half plate lens used on an entire plate. In the catalogs and listings of nineteenth-century manufacturers in general they were more conservative about the coverage of their lenses and excluded, or did not exaggerate including a lot of the blurred area in their coverage specification. Furthermore, for those interested in blur, why not add some vignetting as well?
For use in digital, although it is fashionable to adapt old lenses in a new camera body using adapter rings and homemade solutions, in the case of Petzval this will probably frustrate precisely the issue of the surroundings blur. With a clear area of approximately one third of the focal length an old Petzval lens with 120 mm (already short for the category and difficult to find) will provide a well defined circle of 40 mm. This is already greater than APS-C and almost full-frame, ie the image will come out well defined in the whole field.
To simulate the relationship between focal length, subject size, image size, lens shift, and lens/subject distance, visit this calculator that does exactly that, graphically and intuitively. This can be very useful, especially before buying a lens, because you can check in advance what you can do with it and how it fits your camera. For instance, how much bellow extension is needed for a close-up portrait.
For use with digital cameras the ideal is to buy a new lens, currently manufactured, following the concept of Petzval. There is the Lomography Petzval 85mm f / 2.2, but it seems that its offer is a bit erratic. At the time of writing this post it is out of stock in the official website but is available at B&H. You have to check.
Some Petzval lenses in the collection
Orthoscope, the Petzval landscape lens
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