Rick Beckrich wrote:
>> Didn't realize Father Ansel had made it to sainthood...
Amongst environmentalists, perhaps, if not photographers :-)
>> his starting point with the Blad was Tri-X at ASA (sigh)
>> 200 developed in HC110.
I'm not intending to contradict what Rick - or anyone else - has
said, just using his remark as a jumping-off point for the
following digression:-
>From reading "the Negative", my understanding is that Adams
didn't use empirically-derived film speed ratings, but rather
tested the films using the same sensitometric principles used
in determining "official" film speed (i.e. exposure required
for 0.1 log density above base+fog). The difference was that
he tested the films using *his* combination of developer and
processing technique.
If you look at the speed numbers that he does give in the book,
it is noticable that the majority of them appear to be exactly
*half* the current manufacturers ratings, e.g.
Tri-X 200asa
FP4 64asa
Pan-F 25 asa
one exception is HP5 at 160asa, but I have seen it suggested elsewhere
that HP5 *is* 1/3 stop slower than 35mm Tri-X.
OK, you could say that Kodak and Ilford are routinely exaggerating
their film speeds by 100% (and in a sense this may be true), *but* there
may be another explanation...
Not everyone may be aware that at a certain point (during the sixties, I
believe) film speed numbers *did* double overnight, by agreement between
the film manufacturers (and possibly the standards bodies, ASA and DIN).
This was apparently to counteract the increasing tendancy to overexposure
that was being experienced with the film and equipment of the time, and was
considered to be a simpler solution than that of re-calibrating every
exposure meter in the World.
(I know myself that this did happen, as I have two of my Dad's old Ilford
FP3 cassettes, of very similar age, one marked 64asa and the other 125asa.)
Since Adams had been building up a library of his own film-test data for
decades before this, and presumably paying scant attention to the markings
on the packet, I can't see him going back through all that data and
adjusting
it by 2 to account for this change.
Far more likely that he kept on working exactly as he had before, using the
old
asa scale so that new test data would be directly comparable to the old, and
so that his working methods in the field would not need to change.
It is hence possible that some people, like Ken's example, are rating Tri-X
at 200asa/iso "Because Ansel did" and then finding that they are
experiencing
the same problem (overexposure) that people did who blindly trusted their
meters
back in the sixties, before the change.
I'm writing this all from memory, I'll have another look at The Negative
tonight.
Meanwhile, does anyone have a reference for the ISO speed testing method?
-Brian
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