Bernhard Schmidt invented the reflection telescope with fast focal ratios, without the distorted image and with a wide field of view – the Schmidt camera.

In the first decades of the 20th century the prevailing observational instruments in astronomy were parabolic reflection telescopes. The parabolic shape of the mirror frees the observer from the most important distortion – the spherical aberration – and using the mirrors with a bigger diameter the telescopes, reaching farther distances and giving a better image on the optical axis, can be built. But the image of the parabolic mirror gets worse moving farther from the axis because of other aberrations – coma and astigmatism. This drawback does not allow making photos with a wide field of vision and consequently make overviews of the sky. The problem was originally solved by the optician Bernhard Schmidt (1879-1935) from Naissaare (Estonia) who presented the idea of the reflection telescope with fast focal ration and free of aberration (optical distortion) and with a wide field of view. He designed and built these telescopes also himself (in the Bergedorf Observatory, near Hamburg in Germany). The correction plate in front of the spherical mirror removes spherical aberration. The Schmidt camera caused a revolution in observational astronomy and it is one of the best-known optical systems in the 20th century.

The optical scheme of the Schmidt camera. The spherical mirror and the correction plate guarantee the image without distortion.
Kepler Space telescope, launched on 6 march 2009, is also a Schmidt-telescope.