Monday, March 30, 2009

March 30: Bernhard Schmidt

Bernhard Woldemar Schmidt
March 30, 1879 – December 1, 1935

Bernhard Schmidt was an Estonian Swedish optician who spent his adult life in Germany. In 1930 he invented the Schmidt telescope which corrected for the optical errors of spherical aberration, coma, and astigmatism, making possible for the first time the construction of very large, wide-angled reflective cameras of short exposure time for astronomical research.

When he was 15 years old, he experimented with gunpowder. He packed an iron pipe with a charge, but through a mistake with the fuse the pipe exploded, and he lost the thumb and index finger of his right hand. Despite his mother's attempts to clean and bandage the wounds, surgeons in Tallinn later amputated the whole hand. This event appears to have deepened his reserve and introspection, qualities well noted by his contemporaries in later life.

Schmidt developed an early interest in astronomy and optics. Gradually, he found his true calling, namely the grinding and polishing of highly precise optics for astronomical applications. He seems to have begun the grinding of mirrors sometime around 1901, and thereafter began to sell some of his products to amateur astronomers. By March 1904, he had made so much progress in his new endeavor that after finishing his studies, he was soon in contact with professionals at the major observatories in Germany. His business rapidly took off when noted astronomers such as Hermann Carl Vogel, and Karl Schwarzschild realized the excellence of Schmidt's mirrors for their researches.

During 1927 and 1929, Schmidt participated in two solar eclipse expeditions mounted by the Hamburg Observatory, the first to northern Sweden and the second to the Philippines. It was during this second trip that Schmidt announced to his companion, the astronomer Walter Baade, the most important invention of Schmidt's lifetime, indeed an invention that revolutionized astronomy and optical design in the second half of the 20th century, namely his wide-angle reflective camera.

According to Baade, he had abandoned at least one solution already, when finally he hit upon his ultimate design, which involved a novel, indeed bold departure from traditional optical designs. Schmidt realized that by employing a large spherically shaped mirror (instead of the normal paraboloidal mirror of a reflector telescope) and a smaller apertured diaphragm placed at the center of curvature of the mirror, he could at a stroke eliminate coma and astigmatism. He would be left, however, with spherical aberration which is just as damaging to image sharpness.

Schmidt built his first "Schmidtspiegel"(which came to be known as the Schmidt camera) in 1930, a breakthrough which caused a sensation around the world. He employed a very clever method (the so-called "vacuum pan" method) to make the difficult "corrector plate," so that the system gave superb images. The vacuum pan involved carefully warping the glass lens under partial vacuum and then polishing a smooth curve into it. After release of the vacuum, the lens would spring back into the "Schmidt shape" needed for the camera. No one had ever made a lens in this way before.

Schmidt fell ill at the end of November 1935 and died on December 1. Soon after his death, through the advocacy of Walter Baade when he arrived at the Mount Wilson Observatory in the United States, the Schmidt telescope idea took off. An 18" Schmidt was produced in 1938 and then ten years later, the famous 48" Samuel Oschin Schmidt-telescope was built at Mount Palomar Observatory. This last telescope produced a flood of new observations and information. It proved the brilliance of the Schmidt concept beyond doubt.

Subsequently at Bergedorf in 1955 a large, well-constructed Schmidt was dedicated. The 2-meter Schmidt telescope of the Karl Schwarzschild Observatory was built later and remains the largest Schmidt camera in the world, although more technologically advanced versions have since been produced. The Bergedorf Schmidt was moved to Calar Alto Observatory in 1976.

The Lunar crater Schmidt is named, in part, in his honor.


  1. Great post!

    By the way the 18" Schmidt is at Palomar and it was operational starting in 1936, only to be retired in the mid 1990s a couple of years after its final big discovery - Comet Shoemaker-Levy 9.

  2. Oh, nice bit of info to add to this post! Thanks!