[LargeFormat] ASA jump... when?

[Richard Knoppow]

----- Original Message ----- 
From: "LNPhoto" <LNPhoto@twmi.rr.com>
To: <largeformat@f32.net>
Sent: Friday, February 27, 2004 8:20 PM
Subject: Re: [LargeFormat] ASA jump... when?


> Interesting, I had pegged it about 1954.
> On Friday, February 27, 2004, at 09:21  PM, Richard
Knoppow wrote:
>
   Not that early. I have a 1956 Kodak Reference Handbook
with the old film ratings. Examples are:
Super-XX sheet film, ASA 100
Tri-X sheet and roll film, ASA 200
Plus-X roll film, ASA 80
Verichrome Pan, ASA 80

   In addition to this the film booklet describes the Kodak
method as the one being used.
   A little later (as it says in cheap novels)...  The ASA
fixed mimimum density method was adopted in 1960. The
standard is PH2.5-1960  for some reason I thought it was a
couple of years earlier, perhaps because of the papers
reporting the work. For a complete discussion of the methods
and of why the change was made see:
_The Theory of the Photographic Process_ Third Edition, Mees
and James, New York, 1966, The Macmillan Company.  Chapter
20, "The Interpretation of Sensitometric Results" p437ff

  As stated in my original post the original ASA method,
based on Jones' minimum gradient method, proved too
difficult to use in practice. Jones had studied the results
of a very large survey of prints made from an enormous
variety of negatives to find those that gave a "first
excellent print" based on negative exposure. Because this
method was so difficult to use in practice without
generating excessive errors the fixed gradient method was
studied in comparision by Nelson and Simonds. They found
that when the overall contrast of the negatives were
controlled the fractional gradient method did not have a
significant advantage in predicting the printing results of
negatives. At the time Jones' method was devised and adoped
by Kodak there was little standardization of processing. The
Kodak method has an advantage when this is the case. I don't
have a copy of the Nelson and Simmonds paper here.
  It was not the method of measuring the film speeds which
made the big difference, however, but the dropping of the
one stop safty factor, which had no real utility.


C.N.Nelson and J.L.Simonds, _Journal of the Optical Society
of America_ 46, 324 (1956).

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com