Determination of the speck-order number
of commercial photographic emulsions¹

Klaus Kröber and Ewald Gerth

Received: February 8st, 1969

Going back to theoretical investigations of Burton and Berg as well as those of Gerth on the creation of developable full-specks out of sub-specks the empirically by Mees set up relation of the density S in dependence on the exposure light intensity E for the toe of the characteristic curve

S = const En

is proved at hand of different photographic materials and has been found to be valid in every case.
The exponent n, which hitherto has not been clarified concerning its meaning, is explained as a reaction order number of the kinetic build-up process of developing specks extended over 4 steps. According to the theory this reaction order number - called "speck-order number" - varies only between the limits n = 1 and n = 4. Indeed, within these limits all empirically determined speck-order numbers were found. The speck-order number will be changed generally by influence onto the latent image. As an example for this statement the influence of the pre-exposure onto this magnitude is referred. With increasing pre-exposure the speck-order number decreases down to the limiting value n = 1.

Institutions and addresses of the authors in 1969:
Dipl.-Ing. Klaus Kröber, VEB DEFA Studio für Spielfilme, 1502 Potsdam-Babelsberg, August-Bebel-Str. 26-53
Dr. Ewald Gerth, Deutsche Akademie der Wissenschaften zu Berlin, Institut für Sternphysik,
Astrophysikalisches Observatorium Potsdam, 15 Potsdam, Telegrafenberg

Published in German:

P 33. Kröber K. Gerth E.:
Bestimmung der Keimordnungszahl
handelsueblicher photographischer Emulsionen
Z. wiss. Phot. 63 (1969) 119-132


P 16. Gerth E.:
Analytische Darstellung der Schwärzungskurve
unter Berücksichtigung des Schwarzschild-Effektes
Z. wiss. Phot. 59 (1965) 1-19

Analytic representation
of the photographic characteristic blackening curve
accounting for the Schwarzschild-effect

P 22. Gerth E.:
Zur theoretischen Deutung des Schwarzschildschen Schwärzungsgesetzes -
mit einer Würdigung des Begründers der Wissenschaftlichen Photographie:
Karl Schwarzschild 1873-1916
Wiss. Z. PH Potsdam 10 (1966) 339-410

On the theoretical interpretation of Schwarzschild's law of blackening -
with a recognition of the founder of Scientific Photography:
Karl Schwarzschild (1873 - 1916)

Commemoration of Klaus Kröber:
Dipl.-Ing. Klaus Kröber (born 1905, July 5th) died on Dec. 95th, 1988 at the age of 83. He was one of the leading engineers in the field of film techniques of the nationally owned movie-producing enterprise DEFA, engaged especially in the development of measuring and controlling methods for deriving quality standards of raw film materials. The co-author E. Gerth is deeply indebted to him for a long and true friendship as well as for a fruitful scientific cooperation, giving among other things the incentive to investigate the properties of the photographic emulsion represented by the characteristic curve.

Ewald Gerth, Potsdam, July 5th, 2009