Bernhard Schmidt

By the first decades of the nineteenth century every one of the island’s native families had settled there. Two thirds of the inhabitants were Swedes and the remaining third Estonians, and they lived in three villages: Lõunaküla, the largest, with Lääneküla and Põhjaküla. In Swedish the island is Nargö, and it counted among the Estonian-Swedish settlements of north-western Harjumaa. Piloting ships through the Suurupi strait and into Tallinn Bay had been an island trade since the eighteenth century.

Bernhard Woldemar Schmidt was born here on 11 April 1879 — or on 30 March by the old calendar then in force in the Russian Empire. The two birth dates found in the literature are one date with twelve days between them. His father Carl Constantin Schmidt was a pilot and his grandfather Mathias a fisherman. His parents had married on 6 June 1878 and had five children; Bernhard was the eldest.

The island had a quarantine point from early in the century, a sea-rescue station from 1874 and a school from 1876 — three years before he was born, so there was a school on the island throughout his childhood. What was spoken in it changed during his lifetime. Swedish missionaries had taught the island’s children in Swedish, but under the Russification campaign Swedish was banned outright: the younger children could be taught in Estonian, the older ones received instruction only in Russian. Estonian sources say the family spoke Estonian at home; the English-language reference literature says Swedish was the language of the island and the school and that the Schmidt family also spoke German — in one formulation, German at home. This page does not choose between them. He kept Estonian citizenship all his life, including the years he lived and worked in Germany.

His brother August is the only person who wrote anything down about the boy. He described Bernhard as very quiet, reserved and thoughtful, but always busy with something interesting. The farm where he was born is called Sepa talu; the island’s southern trail passes it. Whether the house standing there now is the one he was born in, the trail’s description does not say. A memorial stone stands by the road in front of the barn known as Omari küün.

Eesti Entsüklopeedia: Naissaar · Naissaare asustamine · Tõnu Viik: Kuulus naissaarlane Bernhard Voldemar Schmidt (PDF) · Monica.ee: Bernhard Schmidt — per aspera ad astra · Wikipedia (en): Bernhard Schmidt, CC BY-SA 4.0 · P. Müürsepp: Bernhard Schmidt – Eestist pärinev XX sajandi silmapaistvaim optik (Tähetorni Kalender 25, 1959) · Naissaar’s southern trail (naissaar.ee)

The English-language tradition says the blast cost him the thumb and forefinger of the right hand; that his mother cleaned and bound the wounds on the island, and that in Tallinn the surgeons then took off the whole hand. The German sources say something else: in 1894 he lost his right forearm. Estonian pages split the difference — the amputation was made in Tallinn, above the wrist. The only scholarly biography, Barbara Dufner’s (Franz Steiner Verlag, 2002), says plainly: his right hand.

The Hamburg Observatory, where he later worked, states on its own page that he lost his right hand and forearm at the age of eleven. On the age it stands alone against every other source found, all of which say fifteen. Exactly what was taken, and how old he was when it happened, cannot be settled from here — so this page does not settle it. One thing is the same in every version: the right hand went.

What no source disputes is what happened next. That same year he built himself a camera and sold the islanders photographs of themselves. A year later he left Naissaar for Tallinn and found work as a telegraph operator — a one-handed teenager’s first paid trade, long before any optics. He taught himself to grind glass, without a master.

From then on every surface he ever finished — the first corrector plate included — is the work of one hand. In the later workshop, hired men did the roughing and he did the figuring himself. One concrete observation about his technique survives, and it is not about strength: P. Müürsepp wrote in 1959 that Schmidt had a rare sense of when to break off the polishing and test the surface. In figuring an asphere by hand the whole art is in the decision of when to lift the tool and go to the test. That is why one hand was enough.

Wikipedia (en): Bernhard Schmidt, CC BY-SA 4.0 · Wikipedia (de): Bernhard Schmidt (Optiker), CC BY-SA 4.0 · Barbara Dufner, Den Himmel fest im Blick (2002) · Tõnu Viik: Kuulus naissaarlane Bernhard Voldemar Schmidt (manuscript, 2004), Tartu Observatory Virtual Museum · P. Müürsepp: Bernhard Schmidt – Eestist pärinev XX sajandi silmapaistvaim optik (Tähetorni Kalender 25, 1959)

The training happened elsewhere. As early as 1903, while still nominally a student, he began hand-grinding mirrors and lenses in a workshop of his own in Mittweida — and not roughly, but to the highest precision. The parabolic mirrors from his workshop started at twenty centimetres and went up. The town began to call him Linsen-Schmidt, lens-Schmidt: the man who ground glass in a back room and sent the results to observatories.

In 1904 the Astrophysical Observatory at Potsdam bought one of his mirrors, and he charged no more than it had cost him to make. The mirror did the selling: new orders came quickly, and before long telescopes from established instrument makers were being sent to him to be put right. By March of that year he was corresponding with the major German observatories. He wrote to Karl Schwarzschild offering to make him a large mirror; out of that unsolicited letter came about ten years of cooperation.

In 1913 Schwarzschild, by then director at Potsdam, wrote to the Prussian Minister of Education asking that the correction of an objective be given to Schmidt, on the ground that “Mr Schmidt is the greater artist”. A state observatory was arguing to a ministry that a one-handed man with no diploma, working alone in a small Saxon town, should be preferred to the trade.

In 1909 he built a telescope for himself. For his own small observatory in Mittweida he made a reflector that lies horizontal, its parabolic mirror 40 cm across with a focus of 11 m — the instrument later called the Uranostat. The optician was now also the observer, testing his own glass on the sky. The years 1904 to 1914 were the good ones: orders kept coming, and his name carried weight among German astronomers. Then the war came. His economic position grew steadily worse, and by the middle of the 1920s the workshop no longer paid; what was left of the equipment had to be sold off. Twenty-five years of independence ended with the tools going for scrap.

Hochschule Mittweida: Bernhard Schmidt · Jan-Peter Domschke, Hansgeorg Hofmann: Linsen-Schmidt (Hochschule Mittweida, 2019) · Wikipedia (de): Bernhard Schmidt (Optiker), CC BY-SA 4.0 · H.-Christ. Freiesleben: Schmidt, Bernhard Voldemar (Complete Dictionary of Scientific Biography, Encyclopedia.com) · Barbara Dufner: Schmidt, Bernhard Woldemar (Neue Deutsche Biographie 23, 2007) · Wikipedia (en): Bernhard Schmidt, CC BY-SA 4.0 · Clyde J. Smith: Schmidt Invents the Corrector for the Schmidt Camera and Telescope (EBSCO Research Starters, 2021)

He had gone looking for the work himself. The German sources call his standing that of a “volunteer collaborator” — an outsider working inside the institution. From 1931 he lived on the observatory site as well. Today the Hamburg Observatory counts him among the most renowned staff in its history. The material from his own workshop — drawings, correspondence, observing books — is still there, in the Bernhard Schmidt Archive.

In 1929 Schorr sent Walter Baade and Schmidt to the Philippines to observe the total solar eclipse of 9 May. The sea voyage lasted five months. Over those months Baade and Schmidt talked at length about a distortion-free wide-field mirror telescope, and it was on that voyage that Schmidt hit on the idea of compensating a mirror’s aberrations with a correcting lens. The German biographical literature traces the coma-free telescope back to exactly those conversations — that is, to a conversation between two men rather than a single flash.

A year later the instrument existed. In 1930 the first Schmidt camera was built in his own workshop at the Hamburg Observatory, and in the autumn he presented it there. The numbers are small and steep: a clear aperture of 36 cm at the corrector plate, a spherical primary of 44 cm — deliberately larger than the aperture, so that oblique beams from the edge of the field still land entirely on glass — a focal length of 62.5 cm — the literature prints f/1.75 for this; the division itself gives f/1.74 (see the tile at the bench above). The plate itself was 5 mm thick. Those are the same numbers you can move one at a time at the bench above, and watch what the rays do.

It reached print in 1931 — not in an astronomical journal but in a trade paper for opticians and instrument makers: “Ein lichtstarkes komafreies Spiegelsystem”, Central-Zeitung für Optik und Mechanik 52 (1931), pp. 25–26. The invention was announced to opticians first, in their own paper. In the years that followed, Schmidt and the Hamburg astronomer Arno Arthur Wachmann took roughly two hundred exposures with the camera onto curved film. He never patented it. And the Finn Yrjö Väisälä had designed the same system as early as 1924, but had set it aside — in a footnote he called the spherical focal surface problematic. Schmidt simply accepted it and bent his film.

Universität Hamburg: Bernhard Schmidt · Wikipedia (de): Bernhard Schmidt (Optiker), CC BY-SA 4.0 · Hamburger Sternwarte: Bernhard-Schmidt-Archiv · Wikipedia (en): Schmidt–Väisälä camera, CC BY-SA 4.0 · Barbara Dufner: Schmidt, Bernhard Woldemar (Neue Deutsche Biographie 23, 2007)

The corrector is not a lens in the ordinary sense. Its thickness varies as the fourth power of the radius: weakly converging in the middle, weakly diverging at the edge, and in one zone between them it does nothing at all. On the first camera the whole figure is about a tenth of a millimetre deep. No ordinary grinding produces such a surface, because grinding naturally gives you a sphere, not a fourth-power curve.

Schmidt’s solution was to make the glass give itself the shape. A thin blank is used as the lid of a vacuum-tight chamber. When the air is pumped out from beneath it, the blank bows inward. While it is held bent, the exposed upper surface is ground and polished to a sphere. Then the air is let back in, the plate springs straight — and the surface that was spherical under load is now the aspheric corrector. German reference works call the finished figure “hutkrempenförmig”, hat-brim shaped.

It works because the deflection of a clamped circular plate under uniform pressure is a fourth-power curve — exactly what the corrector needs. But it is not free. The same deflection also delivers a square term, and always delivers more of it than is wanted: the difference is a weak sphere that has to be polished off afterwards. And the pressure available is capped at one atmosphere. That puts a ceiling on thickness. On his first camera’s dimensions no plate thicker than about nine and a half millimetres can be made this way — set the thickness at the bench above and the gauge tells you how much vacuum it would take.

The difficulty, then, was not the shape but where the zero lands. The literature puts the neutral zone at either 0.707 or 0.866 of the radius, the choice depending on whether the plate is meant to give the best image or to be easier to make. √3/2, that is 0.866, is the place where the steepest slopes of the positive and negative parts are equal — which minimises the plate’s own chromatic aberration and, not coincidentally, how much glass has to be removed at all. A modern review of telescope optics says outright that the technical difficulties came from controlling the lap’s radius of curvature and then the null-power zone. The pan gives you the fourth-power shape for free; where the zero lands is won or lost at the polishing tool.

This part he did not publish. An EBSCO Research Starters article on the corrector (Clyde J. Smith) says that for as long as he lived he kept the details of the plate and of the curved film to himself. He never patented the design — from the moment it was published anyone was free to build it — so the secrecy was a habit, not a commercial strategy. The method was finally written down as a recipe only in 1966: Edgar Everhart, “Making Corrector Plates by Schmidt’s Vacuum Method”, Applied Optics 5 (1966), pp. 713–715. Thirty-one years after his death.

Wikipedia (en): Schmidt corrector plate, CC BY-SA 4.0 · Spektrum: Schmidtsche Korrektionsplatte · telescope-optics.net: Schmidt camera aberrations · Everhart, Applied Optics 5 (1966) 713 · Gerard R. Lemaitre, arXiv 1303.3782: Optical Design and Active Optics Methods in Astronomy · Clyde J. Smith: Schmidt Invents the Corrector for the Schmidt Camera and Telescope (EBSCO Research Starters, 2021) · Tõnu Viik: Kuulus naissaarlane Bernhard Voldemar Schmidt (manuscript, 2004), Tartu Observatory Virtual Museum

The Mittweida college’s calendar page of 2019 (Domschke and Hofmann) adds one scene: outside the house in Bergedorf where he rented a furnished room he is said to have drawn attention, shouting and waving his arms. What happened next is not cleanly available. Some retellings place his last weeks in a hospital, others in an institution; no source reachable from here names the institution. So this page says no more about it than the sources carry. The EBSCO Research Starters biography (Michael S. Ameigh) describes him as a loner — “moody, difficult to approach, and often unpredictable”; the Hamburg Observatory’s own wording is gentler — a gifted artisan who preferred to work alone.

The date is firm: 1 December 1935. The Mittweida page gives the immediate cause as heart failure and pneumonia. The Estonian Wikipedia has him dying of pneumonia in a Hamburg hospital and buried near the Hamburg-Bergedorf Observatory; the German one places the grave in the Bergedorf cemetery beside the observatory. He was fifty-six.

His own words survive because one man went into the workshop after he died. At the end of 1935 Richard Schorr collected and preserved Schmidt’s business correspondence, technical drawings and astrophotographs, and secured what was left in the workshop — which stood inside the main building of the Hamburg Observatory. In January 1936 he published a short notice in Astronomische Nachrichten titled simply “Bernhard Schmidt”. Later the same year he published what Schmidt himself had never written down: how the instrument is made. What had been a secret became, within a year, a textbook.

The invention became famous only about fifteen years later. In 1948 the 48-inch Samuel Oschin Schmidt was completed at Palomar and began the Palomar Observatory Sky Survey almost at once; the first survey plate was exposed on 11 November 1949 and the last on 10 December 1958. By then Schmidt had been dead for nearly fourteen years. His name is on it all the same: the Schmidt camera, and asteroid (1743) Schmidt.

Wikipedia (de): Bernhard Schmidt (Optiker), CC BY-SA 4.0 · Hamburger Sternwarte: Bernhard-Schmidt-Archiv · Wikipedia (et): Schmidti kaamera, CC BY-SA 4.0 · G. Wolfschmidt, Baltic Astronomy 20 (2011) 187 · Wikipedia (en): Bernhard Schmidt, CC BY-SA 4.0 · Jan-Peter Domschke, Hansgeorg Hofmann: Linsen-Schmidt (Hochschule Mittweida, 2019) · Wikipedia (et): Bernhard Schmidt, CC BY-SA 4.0 · Michael S. Ameigh: Bernhard Voldemar Schmidt (EBSCO Research Starters, 2024)