Flare screen
The Scheinerblende is a focusing aid for optical devices invented by Christoph Scheiner at the beginning of the 17th century . It consists of a cover plate with at least two holes ( aperture diaphragm or entrance pupil ) that are attached symmetrically.
A diaphragm with more than two openings is also called a Hartmann diaphragm , after the German astronomer Johannes Franz Hartmann . This aperture is used to measure the beam path of telescopic lenses and its suitability as a focusing aid is only a by-product.
application
In order to focus an optical device, the aperture stop is mounted in front of the foremost lens, a point-like object is aimed at and brought into focus (e.g. a star in astronomy ). As long as the focus has not yet been reached, the (punctiform) object is imaged several times, depending on the number of openings in the dummy aperture. These points move towards each other, the better the focus is; if you focus in the wrong direction, the points move away from each other. When the focus is reached, the points are merged into one point. The optics are now in focus and the bezel can be removed.
In astrophotography z. B. can be reliably focused even with faint objects. However, since a lot of light is lost due to the large-area coverage of the main opening, a bright star is usually first focused and then pivoted to the target object.
The Bahtinov mask is also a focusing aid for amateur telescopes and uses several slots.
The Scheinerblende must not be confused with the Scheiner method ; the latter was only developed by Julius Scheiner in the 19th century .
Web links
Individual evidence
- ↑ Hartmann test for testing telescope lenses . Astrophys. Inst. Potsdam. Retrieved February 16, 2010.