Scheiner degree (or originally Scheiner degree ) is a measuring system developed by the German astrophysicist Julius Scheiner (1858–1913) to determine the light sensitivity of a photo emulsion . The system was first described by him in 1894.
- “Scheiner rotated an opaque disk at a certain speed, from which an opening had been sawn out in the shape of 20 concentric sector rings, the sector angles of which formed an increasing geometric sequence from the outside to the inside. The constant of the geometric sequence was chosen so that the last angle was 100 times larger than the first. The constant thus corresponded to the nineteenth root of 100, i.e. approximately 1.274 ... A standardized light source illuminated the disk from a very specific distance. A cassette was attached behind the pane [...] which held the material to be tested. This cassette was opened for exactly one minute while the disc rotated. The number of the first ring, counting from the inside out, behind which the material had a minimal, precisely defined blackening after development, determined the degree of sensitivity in Scheiner degrees of the material to be tested. The last grade on this scale (which was later to be expanded to include higher levels of sensitivity), grade 20, corresponded to 100 times greater sensitivity than the first. A difference of 3º Scheiner corresponds approximately to double the sensitivity, since the third power of the nineteenth root of 100, namely 2.069 ..., is an approximation of the number 2. "
The Scheiner method, originally intended for astronomical purposes and initially limited to grades 1 to 20, was later improved by Josef Maria Eder (1855–1944). The logarithmic system was widespread in the German-speaking area, but was superseded in Germany from January 1934 by the introduction of a standardized DIN method inspired by it . In other countries it remained in use for much longer. The explanations to DIN 4512 from 1934, which should justify the introduction of the standardized procedure, say :
- “Here, too, it turned out after some time that the measurement method, despite the changes made by Eder, was not able to fully take into account the requirements of practice, so that every manufacturer […] had to determine the sensitivity in degrees of Scheiner according to his own system , often very much primitive way by […] comparison with products from other manufacturers. The apparent usage degrees determined in this way no longer have anything to do with the originally worked out measuring method according to Scheiner. [...] As a result, there has gradually been an inflation in degrees of sensitivity for which Scheiner's method gives nothing more than the name. "
Comparison with later sensitivity data
Similar to later DIN methods, an increase in the sensitivity information in Scheiner degrees by 3 ° corresponds approximately to a linear increase in sensitivity by a factor of 2.
Scheiner degrees can easily be converted into DIN degrees (according to their definition according to DIN 4512: 1934-01 or DIN 4512: 1957-11) by subtracting 10 from the Scheiner value. 16 ° (European) Scheiner degrees corresponded to about 6 ° DIN, 19 ° (European) Scheiner degrees to about 9 ° DIN.
The value is not clear, however; For example, 8 was deducted from the old Practos II light meter from Hans Tönnies, Hamburg, for conversion, and a large number of other Scheiner adaptations were common in other countries.
(Due to the change in the definition of DIN degrees with DIN 4512: 1961-10, earlier values can only be converted to today's dimensions to a limited extent. If the material is black and white negative material, the sensitivity of which is to be expressed in Scheiner degrees in today's ISO values, one must Add another exposure level (i.e. 3 °); in this case, 16 ° Sch. today would correspond to ISO 12/9 ° and 19 ° Sch. straight ISO 24/12 °.)
That around 1925 with 18 ° Sch. Normally sensitive black and white film material would have a film sensitivity of 8 ° DIN in the units of measurement customary up to 1960 (this in turn would correspond to 11 DIN according to the definition according to DIN 4512: 1961-10 or today's ISO 10/11 °).
- Martin Riat: Graphic Techniques - An introduction to the various techniques and their history . E-Book, 3rd German edition, Burriana, Spring 2006 ( PDF ), based on the Spanish book: Martin Riat: Tecniques Grafiques: Una Introduccio a Les Diferents Tecniques I a La Seva Historia . 1st edition, Aubert, September 1983, ISBN 84-86243-00-9 .