Emil-Heinz Schmitz. Handbuch zur Geschichte der Optik. Ergaenzungsband. 1, Das Fernrohr. Bonn: J.P. Wayenborgh, 1982. Pages 175-187. Translated by Ilse Roberts, edited by Peter Abrahams Textbook of the History of Optics. Supplement 1, The Telescope. The Telescope for Both Eyes - for Observation of Earth and Sky. Page 175. Early telescopes were mainly instruments for use with one eye, since for astronomical telescopes, the main goal was to get sufficient magnification, and it was less important to perceive 'spacial realisation' (depth perception). Only when the latter was desired, was the construction of binoculars necessary. We already learned that after the invention of the dutch telescope, Lipperhey received the patent for his instrument only after he had built one for the use of both eyes. As can be seen from the documents of the Generalstaaten, he introduced this binocular in 1608 and delivered two more at the beginning of 1609. Shyrle de Rheita , in the middle of the 17th century, built Keplerian telescopes, but those improved by him were mostly binocular terrestrial telescopes. He pointed out the advantages of such telescopes, since 'objects seem larger and lighter when observed with both eyes'. This physiological effect is also observed without a telescope. But more important is the depth perception with a binocular. Schyrle de Rheita designed interpupillary adjustment and intended to converge the optical axes of the tubes. He used for this purpose a rack and pinion device. Daniel Chorez (working dates 1616 - 1625) and P. Cherubin d’Orleans (1613 - 1697) built telescopes with devices which adjusted the distances between the two tubes to the eye spacing. Cherubin d’Orleans described several such constructions (La dioptrique oculaire, 1671. La vision parfaite, 1677.) where the tubes can be adjusted symmetrically to each other. To gauge the distance between the eyes, he constructed a pair of glasses, where both eyes were covered except for two tiny holes. The holes could be manipulated so that the two pinholes merged, when one could observe an object in the distance with both eyes. Edward Scarlett proposed in 1738 to connect two Gregorian reflecting telescopes to create a binocular. The simple hinge commonly used in dutch binoculars was built in 1758 by the Venetian Domenico Selva. His son Lorenzo Selva (circa 1716 - 1800), who earlier ground periscopic lenses (perioskopische Linsen) in Venice, later constructed such binoculars with achromatic objectives. But this instrument did not become popular, not even when the tube was shortened using achromatic lenses. Johannes Zahn mentioned in his publication of 1685 (Oculus artificialis teledioptricus) several kinds of binoculars. Binoculars for terrestrial use were commonly used since the end of the 17th century. We learn from H. Kraus (Zur Geschichte des Perspektiv- und Brillenhandels; Deutsche Mechanische Zeitung, 1912, pp117ff) that such binoculars from southern Germany were on the market since 1741. The Dresden Optician J. Fr. Meyen sold such 'double perspectives' in his store in 1764. During 1786 - 1787, Friedrich Wilhelm Herschel undertook a number of experiments to observe with both eyes using his telescopes, but he did not return later to this endeavor. The French optician Jean Gabriel Augustin Chevalier (1778 - 1848) marketed in 1807 dutch binoculars with achromatic objectives, but without having much success. An important date is August 19, 1823, when the optician Johan Friedrich Voigtlaender (1778 - 1857) received a patent in Vienna for his binoculars with fixed bridge and single position of the oculars (Fr. Voigtlaender, Fuenfjaehriges Priveligium auf die Erfundung der Doppel-Theater- Perspektive, 19 August, 1823). The title of the official description was: 'Invention of the 'Doppel-Theaterperspektive' where both eyes see at the same time the same object, and so offer more light, distinction, larger field of view, and greater magnification than the common perspective, even for far and near sightedness and even for two different eyes.' The introduction of these new binoculars is documented by a description from April 1825 by Voigtlaender himself, which obviously was destined for ads in newspapers, price lists or something of the sort. During his apprenticeship in England, Voigtlaender learned the working methods of the English opticians. He introduced a design for binocular theater glasses which became very popular and made the opera glass an important trade article. Voigtlaender was an extremely busy craftsman, well informed in his profession. After the death of his father (Johann Christoph) he took over the 'precision mechanical' factory founded in 1756. In March 1807 the municipal council of Vienna gave him the permission to produce mathematical, optical and mechanical instruments. It might seem strange to us that he belonged to the Viennese Turners’ Guild, though probably appropriate for his shop. Voigtlaender successfully took part in the rise of optics which started in his time. In 1815 he began to replace the wooden tubes of optical instruments with metal tubes, and at the same time he used the improved optical lenses produced by Fraunhofer. Because of his quality work he soon became well-known and received orders from the Viennese Court and the town of Vienna. In 1835 the emperor of Austria gave him a silver service medal. Soon after that the learned mechanic retired from his business, succeeded by his son, Peter Wilhelm Friedrich Voigtlaender (1812 - 1878), who became famous in photography. One and half years after Voigtlaender, the Viennese optician B. Wiedhold and the binocular producer A. Schwaiger also received protection for a similar connection of two tubes which could be adjusted to the eye distance of the observer. (B Wiedhold und A. Schwaiger, Fuenfjaehriges Privilegium auf Verbesserung der Voigtlaender'schen Doppel-Perspektive, 15 March, 1825.) All these binoculars were mainly for right-eyed theatergoers (rechtssichtige Theaterbesucher); and they were mostly made with achromatic lenses. In Paris, France, the optician J. Ph. Lemiere received a patent for the simultaneous focusing of both oculars. His binocular realized the central focusing screw, commonly used today, and his original invention, the linkage between tubes across the bridge, so that as one is screwed in or out, the other tube moves in tandem. (A. Koenig, Fernrohre und Entfernungsmesser.) French binocular opera glasses soon dominated the world market. Even the famous English opticians and instrument makers recognized the French opera glasses to be the best in world. The English spectacle maker and optician J.T. Hudson wrote about this in 1834, that the quality of the French glasses and their outfits were unsurpassed (Spectaclaenia, 10th ed., London, 1834). Thus, imports were in extraordinary quantities and there were hardly any opticians or jewelers in Great Britain who didn’t offer French opera glasses. Often the eyecups were replaced with blank rings instead of French inscriptions, since people didn’t like to buy foreign products. As time went by, many improvements were made in binoculars, but most probably didn’t find approval right away. Only after the middle of the 19th century did the demand and production increase. The increase in magnification achieved then was significant in this success. (M. von Rohr, Die binokularen Instrument, p40, 42, 1920) The Parisian manufacturers still dominated in the production of these instruments, and the German shops found plenty of opportunity at the world exhibition in Paris of 1867 to get acquainted with existing models of binoculars, and, for example, found out 'that the common opera glass needed an adjustment at the fulcrum distance of the user' (interpupillary distance). In this context, Moritz von Rohr (page 136) notes the headline of the paragraph in question from the price list of Emil Busch in Rathenow: 'Travel, military and hunting perspective with adjustable axis distance for both eyes (center axis)'. Schultze & Bartels in Rathenower listed in their 1873-1875 catalog of 'Military, Marine, and Travel Telescopes for Both Eyes', a model with 27 mm objectives, 16 power magnification, and thus apparently an exit pupil of 1.7 mm. 'The hinge for the adjustment of the eye distance is expressively mentioned and one can deduce a rather small length of the usable instrument, since only two extensions are given.' Binoculars for astronomical observations were seldom produced and used. In 1848 the Englishman Vallack proposed one of the first binocular astronomical telescopes, where the tubes were reflecting telescopes (Binocular construction in Newtonian reflectors; Monthly Notices 8, 1848, pp139ff). Depth perception was of course absent when observing stars (von Rohr p64). In the fall of 1858 the Parisian optician A.A. Boulanger, in partnership with M. Ph. Poudrilhe, patented an 'astronomical double telescope'. Essentially it consisted of two parallel tubes, which at the ocular end had been fitted each with a pair of 'readout prisms' (Ableseprismen). The two inner prisms could be separated from each other or brought together, to adjust the double tubes to the eye distance of the observer. They could also be tilted on the horizontal axis, so that the angle of view into the binocular allowed a more comfortable position of the head (von Rohr p90). (A.A. Boulanger et M. Ph. Poudrilhe. Un binocle astronomique double et simple. Brev. d'inv. 38481, 25 October 1858; del. 26 November 1858). Prisms are used to erect the image. Page 179. We have seen that when inserting an erecting lens system into an astronomical telescope for the purpose of terrestial observation, a considerable lengthening of the telescope has to be suffered. Therefore, circa 1850, the Italian Ignaz Peter Paul Porro (1801-1875) developed the idea of using prisms in a Keplerian telescope. He patented this invention in 1854 in France and England. This patent document comprises two groups of ideas. At first, the redirection and reversal by prisms is explained. We also find here the two Porro erecting systems for telescopes, and in addition, the sighting device (Visiervorrichtung), a proposal for a rangefinder, and more. The second section refers to the additional illumination added to the light path by a system of mirrors, used to illuminate scales for micrometers. (Patent titled 'The use of total or common reflection of light from surfaces, alone or in combination with refraction.) Ignazio Porro, the son of an engineer-lieutenant joined the Artillerie as a cadet and retired in 1842 as a major in reserve. During his service, he was, after 1822, frequently occupied with surveying, and he was encouraged to improve the instruments. But his inventiveness was mainly developed in the Institut Technomatique, founded in Paris in 1847. In the beginning his relation to the scientific community was very good, but this deteriorated more and more with the passage of time. He returned to Italy in 1861, and in Florence was entrusted with an instructional course for Tachimetry, whereby he was given the use of the shop facilities of the school for the purpose of constructing instruments. In 1863 the Technical University of Milan made him professor of Surveying Theory. But the 'Tecnomasio italiano' founded there did not offer him success. Also, the Filotectina in Turin, founded in 1865, was not successful until developed by his pupil Salmoiragh. Porro died in poverty, but his work related to telescopes made him famous in optics to the present day. Porro described his first prism reversal system as follows: 'I use for it a piece of glass, either singly or of several pieces; it has several flat polished planes which the light penetrates, entering and exiting at the same angle through two flat planes. The light experiences total reflection four times, at right angles, during its way through the glass. If one observes objects through such a glass (prism), the objects appear to be standing on their heads and free of colors. It is therefore sufficient to install such a piece of glass between the ocular and the objective of an astronomical telescope, if one wants to transform this instrument into a common terrestrial telescope with erected images.' 'The exterior form of my 'upright glass' (Aufrichteglases) is a bit complicated but free of the unreliability of the existing means. This procedure allows a great intensity of light, because the light enters in vertical direction; besides that it has the advantage of being able to shorten the length of the telescope, while the other known means for the erection of the image produce a greater or lesser elongation. The new combination is likely to be mostly used at sea.' The practical construction of the Porro reversal system consists of two right angled prisms whose hypotenuse surfaces are positioned towards each other. The orientation of one prism is 90 degrees to the other. The reflection in the interior of the prism occurs by total reflection at the two surfaces, which are not silvered. Porro’s proposal, to make the reversal system out of one piece of glass, encountered great technical difficulties. The telescope created by Porro with this reversal system, also named Longue-vu-Cornet, was designed for monocular use. The instrument had an aperture of 30 mm and 15 power magnification. The ocular could be adjusted for focusing by a handle on the tube. Porro is reported to have also produced, in the same design, a marine telescope with 40 and 60 mm aperture, at 70 or 90 cm focal length, and 15 or 30 cm overall length (Baulaenge). (A. Koenig, Die Fernrohre und Entfernungsmesser, 1937, p235. Ueber Porros Erfindungen, in: Deutsche Optische Wochenschrift 1949, p145. R. Riekher, p275.) The second reversal system was described by Porro as follows: 'I achieve the desired magnification with complete achromacy and a high intensity of light when I connect three prisms as follows: The first is an achromatic right angled isosceles prism with a slightly curved surface. Its shorter surface is positioned horizontally, and its hypotenuse surface totally reflects. The second prism is a simple right angle isosceles reflecting prism, and it lies under the first at a variable distance. It can be oriented in different ways depending on the requirements of an erected or reversed image. It reflects the light from the objective lens only after the light passes through the first prism, and it passes the image to the third prism with a change of orientation following the double reflection. If one views through this combination, distant objects appear magnified and, according to the positions of the reflecting prisms, either reversed or erected as in a good telescope. The field of view can be increased with a small additional lens. The width of the instrument, for example with a magnification of 10 to 15 times, is not over 3 cm, while its extended height is about 10 cm, and it is therefore comfortable to hold.' Rieker notes (p275) 'Porro intended to transform the entrance surface of one prism to an objective, and the exit surface of the other prism, to an ocular. The form of the prism system, as described, is shown in the picture (Porro II). Telescopes equipped with this reversal system were astonishingly small compared to long terrestrial telescopes. They consisted of a small round handle in which the lower prism was placed, and an added head with the two upper prisms, on which ocular and objective were fastened. Focusing was done by moving the lower prism with a small handle. Two telescopes of this kind, named the Lunette Napoleon III were personally given by Porro to the emperor Napoleon III on February 22, 1855. This Lunette Napoleon III had ten power magnification and a field of 3 degrees, and therefore an apparent field of 30 degrees.' One would expect that Porro’s handy invention caused an upheaval in the construction of telescopes. But he had little luck or success with it, even though he was an accomplished expert, and his optical instruments were constructed according to design. According to Moritz von Rohr (Theorie und Geschichte des photographischen Objektives, 1899, pp113ff) 'the use of his grinding and polishing machines, which were supposed to give a much greater precision, constituted a further deviation from the customs of the French opticians. His relations with the scientific community were at the beginning very good, as already mentioned, and he did achieve wide spread recognition for to his activities. But over time, his relationship with men of science deteriorated, as far as we can determine because of a careless advertisement from Porro; and in the middle of the year 1859 there was a Report of the Commission, by H. de Senarmont, which contained a sharp condemnation of the working methods and the character of Porro'. Probably because of this, and because Porro was not particularly versed in optical designs and didn’t know how to improve production methods, his prism constructions did not find lasting usage and were soon almost completely forgotten in the field of practical optics. One of Porro’s early artisans, A.G. Hofmann, Paris, built telescopes with prism reversal systems - monocular instruments with a reticle for distance estimations, but Hofmann didn’t have much success with these either. This novelty did not impress scientists nor practical opticians and was considered more as an oddity, although they were described in Bonnardot’s popular book about the telescope of 1855 and also in the 8th edition of Eisenlohr’s Handbook of Physics of 1866. In 1859 the optician A.A. Boulanger reconsidered the Porro idea and received a patent on a 'Feldstecher' consisting of two Porro prism telescopes, for which he proposed the name Neojumelle or Binoclie Prismatique a Images Droites. (A.A. Boulanger, Une neojumelle, Brev.Fr. 41957, 24 August 1859.) (G. Witt, Ueber Handfernrohre, in Himmel und Erde 12, 1900, pp173ff. M von Rohr, Die binokularen Instrumente, 2nd ed., 1920, p90). This instrument had a fixed distance between the objectives, and the oculars could be adjusted to the interpupillary distance of the user; the oculars along with with the prism system were rotated about the optical axis of the objectives using a central wheel and threaded rods. Boulanger had this binocular telescope produced by the factory of Luquin and L’Hermitte, founded in 1840, owned by E. Lacombe after 1868, and run by L. Lacombe Fils since 1895. To achieve increased depth perception, W.Hardie proposed in 1853 the combination of a telestereoscope and two magnifying telescopes (W. Hardie, The telestereoscope, Philosophical Magazine 15, 1858, pp156ff). But he consulted the optician Adie, of Edinburgh, who did not recognize the importance of this proposition, and no manufacture was attempted. Similar thoughts by A. Claudet did not lead to a practical improvemnt, since during that time the active scientific occupation with binocular telescopes did not find any practical manifestation. (A. Claudet, On the angle to be given to binocular photographic pictures for the stereoscope. 23rd. Meeting British Association at Hull, 1853, number 4. Du stereoscope et de ses applications a la photographie et derniers perfectionnements apportes au daguerreotype par F. Golas, XI, 1853. M. von Rohr, p278.) Porro’s invention made little impression anywhere. Even the first German attempts, in 1865 by Emil Busch in Rathenow, to produce such monocular telescopes with the Porro prism reversal system did not lead to any notable success (K. Albrecht, Der aelteste Busch-Prismen-Feldstecher. DOW 10, 1924, pp612ff). Thus, the failure was not only caused by the persona of Porro. Technical procedures were not ready to solve the problems - it was not possible to produce quality prisms in large quantities, and glass was not yet sufficiently transparent. In 1873 Lafleur and Roulot used the ideas of A.A. Boulanger and Oh. Poudrilhe, to join two oculars with a single objective using a pair of rhomboid prisms, for binocular viewing. Such instruments were introduced under the name Lunette Prismatique. (Lafleur et Roulot, Un systeme de lunette biprismatique. Brev. d'Inv. 99786, 7 February 1873. Cert. 1, 7 May, 1873. Cert. 2, 3 September 1874. Descr. 3, 1873, 7, pp28ff.) Since 1870 the Parisian optician Camille Sebastien Nachet (1799-1881) was occupied by the production of a binocular telescope with reversal prisms, which he called Jumelle Prismatique. (C. et J. Nachet, Une jumelle prismatique. Brev. d'Inv. 109232, 14 August 1875; 6 November 1875.) This instrument differed from the Boulanger Neojumelle by a different form of the prism body. Also the interpupillary adjustment had been simplified to a rotation of the individual oculars. All interpupillary distances over 57 mm could be matched, with the objectives spaced at a distance of 83 mm, whereby a certain increase in stereoscopic appearance was achieved. Even these double telescopes were not popular with buyers. (M. von Rohr p172). Moritz von Rohr (p174) reported on a double telescope by Carston Diederich Ahrens, who applied for an English patent in 1884, for an instrument that corresponded to the Boulanger invention; a patent that was never completed. To judge from an example at Zeiss in Jena, the failure of this instrument is quite understandable, since the advantages of image erection by Porro prisms were not used for the shortening of the tubes nor for the increase of the quality of the image. These prisms were used only for a small adjustment to the interpupillary distance, in the manner which A.A. Boulanger had already envisioned 25 years before. (C.D. Ahrens, Improvements in the construction of erecting binocular prism, English patent 1710284, 31 December 1884.) Only with Ernst Abbe (1840 - 1905) did the prism telescope receive its due recognition. Already in 1873, Abbe had developed a monocular handheld telescope with a prism reversal sytem, and shown it at the Vienna trade fair, without finding anybody interested in it. In 1893, he returned to the thought, conquered the many technical difficulties, and eliminated several faults of the first construction. (E. Michaelis. Die ersten Feldstecher. Zeiss-Werkzeitung vom Oktober 1941.) The firm of Carl Zeiss, during the business year 1884 - 1895, produced such a field glass for general use, and the new merchandise was a great success for Zeiss. (Fr. Schomerus. Geschichte des Jenaer Zeisswerkes 1846-1946. 1952. pp91ff.) After this example several other optical firms built such field glasses in the following years. We would deny recognition to perhaps the most important 'Optiker' of all times, if we did not tell about his life. Ernst Abbe, son of a laborer born in Eisenach, went at first to the common school. Soon his teachers noticed his eagerness and his extraordinary giftedness. The employer of his father made it possible for the boy to attend high school. He graduated with an excellent record. His knowledge of mathematics and physics were lauded. 'His excellent works in optics proved that he could treat even a phyiscs problem with the help of higher mathematics, which had never been done at the school and was not a requirement.' In the summer of 1857, Abbe matriculated in Jena as a student of mathematics at the Sachsen Weimar State University. Later he studied mathematics and physics in Goettingen. Barely 21 years old, he received his PhD degree summa cum laude. After temporary employment at the Goettingen Planetarium and in the physics society of Frankfurt, in 1865, he became a professor in Jena. Seven years later he was tenured. For thirty years he taught at the university, and towards the end he concentrated on geometric optics. His connection with Carl Zeiss began in 1866, when his major works in optics began. He devoted all his efforts to the Zeiss company. His nearly superhuman accomplishment, the uncounted numbers of all night sessions, and the strong use of narcotics, slowly destroyed the health of this strong willed man. In the spring of 1903 he resigned. He died at the age of 65. His name will be not be forgotten in the field of optics. =========================== home page: http://www.europa.com/~telscope/binotele.htm