Hartmann mask

The aperture Scheiner is a beginning of the 17th century by Christoph Scheiner erfundere focusing aid for optical devices. It consists of a cover plate with at least two holes ( aperture stop or the entrance pupil ), which are mounted symmetrically.

A diaphragm with more than two openings is also called Hartmann- aperture, after the German astronomer Johannes Franz Hartmann .. This diaphragm of the optical path of the telescope lenses is to measure used and the suitability as a focusing aid is just a byproduct.

Application

In order to focus an optical device, the Scheiner aperture is mounted in front of the front lens, targeting a point-like object and focused ( eg a star in astronomy ). While the focus has not yet been reached, the ( dot-shaped ) object is imaged several times, depending on the number of openings in the diaphragm Scheiner. These points move towards each other, is the better focused; when focusing in the wrong direction move the points away from each other. On reaching the focus points are merged into a point. The design is now in focus and the aperture Scheiner can be removed.

In astrophotography, for example, can thus be reliably brought into focus even in faint objects. Because of the large area coverage of the main opening, however much light is lost, usually found only focus on a bright star and then pivoted to the target.

The Bahtinov mask is also a focusing aid for amateur telescopes and uses multiple slots.

The Scheiner blinder must not be confused with the Scheiner - method; latter has been developed only in the 19th century by Julius Scheiner.