Cross aperture

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Cross screen made of matt filter disc and adhesive film
Oral mucous membrane cells, recorded in simple brightfield
Oral mucous membrane cells, recorded with a diaphragm

The Kreutz aperture (also Kreutz diaphragm or diaphragm according Kreutz or sector shutter is) a round frosted glass filter disc with a more or less opaque taped surface, which can be an approximately crescent-shaped area at the edge of the wafer free. It causes an oblique illumination of the objects observed in light microscopes .

history

The cover was named after Dr. Martin Kreutz, who first described this diaphragm in 1994 at the 5th International Microscopy Days in Hagen and then in 1995 in an article in Mikrokosmos , a specialist journal for microscopy. With this, he made - slightly modified - a previously known method of oblique lighting popular again.

Comparable diaphragms and their use to increase contrast by means of oblique lighting were, for example, mentioned and illustrated in an English microscopy textbook in 1920.

application

The pane is introduced into the illumination beam path of a transmitted light microscope in such a way that it lies approximately in the plane of the aperture diaphragm .

By means of this diaphragm it is possible to achieve a spatial effect (3-D effect, relief effect) and an increase in contrast in low-contrast phase objects , somewhat comparable to the image with differential interference contrast . The increase in contrast is based on the fact that the use of the cross diaphragm causes the illumination to fall essentially obliquely onto the phase object and, as a result, the waves interfering in the image plane generate an asymmetrical distribution of brightness around the image point. This interference image is not almost extinguished by the corresponding mirror-inverted interference image of an oblique illumination from the opposite direction - as in the case of symmetrical brightfield - and therefore generates a higher-contrast distribution of brightness with one-sided relief.

The lighting with a cross aperture is a special form of "leaning lighting".

See also

literature

  • Klaus Henkel: The Microfibre , 2003 (PDF file; 3.28 MB)
  • Michael Volgger: Light microscopy, theory and application. 2008, p. 131. (pdf download from this website).

Individual evidence

  1. ↑ Edmund J. Spitta: Microscopy. The construction, theory and use of the microscopy . 3. Edition. John Murray, London 1920, p. 195–201 (available online at archive.org ).
  2. ↑ Martin Kreutz, A modified oblique lighting , 1994
  3. ↑ Martin Kreutz, A modified inclined lighting . Mikrokosmos 1995/4, Elsevier, pp. 197-199.