Dark field principle

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Dark field principle: The negative appears as a positive against a black background

The dark field principle is an optical effect that is used in photography and microscopy , among other things . Due to the dark field principle, an underexposed negative appears as a positive against a dark background .

History and Development

The dark field principle was first described by John Herschel in 1839 .

Hamilton L. Smith took advantage of this effect when he developed the ferrotype , also known as tintype , in 1856 . This is a collodion wet plate negative that is produced using the direct positive photographic process : A black lacquered iron sheet is used as the layer support for the collodion emulsion , which serves as a background for the unique negative; the negative then appears as positive due to the dark field principle.

The following photographic processes use the dark field principle:

At the end of the 19th century, the Austrian chemist Richard Zsigmondy and the physicist Henry Siedentopf in Jena developed an ultramicroscope based on the dark field principle. By improving this principle, he constructed the immersion ultramicroscope in 1912, which was the first to make particles with a size of a millionth of a millimeter visible.

See also

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