A COROLLARY TO PHOTOGRAIPHY - 1
Whatever has so far been presented in
the name ‘Photography’ may need some clarifications over the typical terms in
vogue in the trade.
ASA = AMERICAN STANDARDS ASSOCIATION
[GUIDE LINE] on the adoption of Film speed for customers to recognize ‘the
sensitivity’ of the film. The scaling is Arithmetic in calculation ; it gives a
straight forward meaning like a film rated at 400 ASA is double as sensitive as
that of one rated at 200 ASA and 4 times that of one rated at 100 ASA. The
British film industry fell in line using BS [British standards] as their norm
.100 ASA =100 BS .
The GERMAN PHOTO INDUSTRY had its own scale –THE DIN =Deutsche Industrie normen which is designed on Logarithmic scale. The numeral of the film rating is with a superscript [o] indicating degree sign to signify its log status. Being on a log scale, the numbers do not indicate relative sensitivity features among films. The following examples would explain the difference between the Arithmetic [ASA] and the Log [DIN] scale. The two ratings are presented side by side , so that the sensitivity of films –as expressed by the2 schemes can be known. ASA /DIN read as under:
100ASA/ 21ODIN; 200 /240;
400/ 27O, 50/ 18O; 25 /15O 800/ 30O and so on. An increase of 3
units on DIN scale means doubling of film speed unlike in ASA scale where
numbers are easier to comprehend.
HYPO =Sodium thio sulphate –the fixer
VIGNETTING: Loss of image details
along the outer rim of the negative [DUE TO SOME LENS ABERRATION].
PINK WASH The act of applying transparent ‘pink dye’ to
shield from light passage through negative to minimize the effect of deep
darkening in the positive image.
SPOTTING : An act of blocking holes/
scratches on negatives with a grey opaque dye to prevent faithful transfer of
blemishes to final positive during printing.
K.Raman
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