From: Les Newcomer (lnphoto@ismi.net)
Date: 02/11/00-04:28:50 PM Z
Roger,
There is a book called the "Handbook of Photography, it was published in
1939 and it can take just about any simple question and turn it into an
incredibly accurate jumble of mathmatical formulas that will take you a
week to under stand. For expample:
"The various film-speed systems are not based on the same fundamental
use of the D-log E curve (they changed it to Dlog H curve later), and
the film-speed numnbers do not progess uniformly in the various systems;
in some cases the speed number progress proportionaltely to the relative
speed, in others they do no. It is possible, however, to devise a
relationship between the various film-speed numbers, as given in
Appendix B, altohough such relations are to be regarded as being, at
best, rough approximations. If Sa is some arbitrary or relative
silm-speed or film -sensitivity number and Sn is the film speed or
sinsitivity in the 'n' system of rating, then the various film -speed
numbers will be related to the relative sensitivity by the equations
given in Table I."
Film-speed system Film
speed symbol Film speed
related to relative film speed, Sa
Weston
Sb
Sb=.223 Sa
American H and D (k=10)
Sc
Sc=5.8 Sa
European Hand D
Sd
Sd=27 Sa
Watkins
Se
Se=10.65 Sa
Wynne
Sf
Sf=10.9 (square rt of) Sa
Burroughs-Wellcome
Sg
Sg=2.83/Sa
American Scheiner
Sh
Sh=(1+9.5 log10 Sa)
European
Scheiner
Si
Si= (5+9.5 log10 Sa)
Eder
Hecht
Sj
Sj=(43+24 log10 Sa)
DIN
Sk
Sk=[(10 log10 Sa) -7] /10
Eastman*
Sl
Sl=1.165 Sa
"* The film-speed values for the Eastman Kodak Co. minimum-gradient
film-speed system are based on published data for aonly a few emulsions,
from which it was determined that the Kodak numbers are approximately
five time the Westion Speed numbers for the same emulsion."
Sa is any number you want to come up with. Appendix B is a table that
lists Sa as 'relative speed values" much like that of Iso numbers today
except they start with 1 and then play out the values for all of the
systems listed above except for Kodak. I've repeated the table and
replaced the "film speed symbol" with the value equal to 100 on the
relatve speed column
Film-speed system Film
speed symbol Film speed
related to relative film speed, Sa
Weston
23.3
Sb=.223 Sa
American H and D (k=10)
580
Sc=5.8 Sa
European Hand D
2700
Sd=27 Sa
Watkins
1070
Se=10.65 Sa
Wynne
F/209
Sf=10.9 (square rt of) Sa
Burroughs-Wellcome
0.028
Sg=2.83/Sa
American Scheiner
20.0
Sh=(1+9.5 log10 Sa)
European Scheiner
25.0
Si= (5+9.5 log10 Sa)
Eder
Hecht
92
Sj=(43+24 log10 Sa)
DIN
13/10
Sk=[(10 log10 Sa) -7] /10
Eastman*
116.5*
Sl=1.165 Sa
I've found if you print theis out and sleep with it under your pillow it
really does help understanding it.
Les
> Hi!
> I was wondering if anyone knows just when we began to
> use ASA numbers? I was looking at 1939-1950 magazine
> ads for Ansco and Kodak sensitive materials and the
> the lack of speed information is, well, noticeable.
>
> Any one know of a chart listing the equivalent speeds
> for the former H&D speeds with the ISO (or ASA)
> speeds?
>
> Thanks... and sorry about the off topic(?)subject, but
> the recent inquires of that um... commercial entity
> just seemed to open this can of worms...that stuff
> about international standards of light and...well if
> you have any information, use your own discretion as
> to whether it should go on or off list. Thanks.
>
> Ray
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