[rollei_list] Re: B&W film developing
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Tue, 13 May 2014 19:45:12 -0700
----- Original Message -----
From: "Chris Burck" <chris.burck@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Tuesday, May 13, 2014 12:58 PM
Subject: [rollei_list] Re: B&W film developing
Fascinating. Can't help but wonder what would have been,
had Kodak been
unable to breach Agfa's patents.
On May 12, 2014 11:52 PM, "Richard Knoppow"
<dickburk@xxxxxxxxxxxxx> wrote:
My reference books are hiding in storage. Both AGFA and
Kodak were working on color film from early on. Both had
come up with additive films using a dyed starch reseau and a
lenticular film. Both had problems especially in the area of
duplicating.
The main difference between the AGFA and Kodak
multi-layer film was the method used to keep the couplers
and resulting dye particals from wandering in the emulsion.
AGFA attached the couplers to very long chain molecules that
were too big to move in the gelatin. Kodak encapsulated the
couplers in tiny oil droplets that served the same purpose.
The two types of film require somewhat different methods of
processing. The oil droplet film requires the color
developer to have a solvent in it capable of penetrating the
droplets. Both types of film were made for a few decades but
eventually the Kodak type won out and is the type which
currently survives. The method of sequestering the coupler
is the same for both negative and reversal films. From what
I can find on the web it appears that both Kodak and AGFA
had working films using incorporated couplers by the mid
1930s but Kodak evidently was not satisfied with theirs and
held off producing it for a few years. Note that Kodachrome
does not have incorporated couplers; rather the couplers are
in the reversal developers. Note developers plural because
there are three of them. The development process is
extremely complex but resulted in very good color quality.
None of these films had any sort of masking. Kodak devised
color masking about the late 1940s by means of colored
couplers. The purpose of the masking is to compensate for
spurious transmission by the dyes in order to improve both
color purity and accuracy. Masking originally could be used
only in color negative films and the colored coupler method
is still confined to them but another method of compensating
for the dyes was found by allowing interlayer reaction so
that the production of dye in one layer results in a
reduction of dye in the adjacent layer. This method can be
applied to either negative or reversal films.
Someone mentioned that some digital cameras make three
bracked exposures to extend the dynamic range. In fact, many
films, both B&W and color have two or three layers of
emulsion, color films have them for each color, of differing
speed, for the same purpose, that is extending the dynamic
range.
BTW, I have heard the story before that Kodak was able
to use AGFA patents during WW-2 in order to make color
aerial film. I think if this is true its because the AGFA
film was ready for production while Kodak was still
researching. At the time we entered WW-2 as a combatent AGFA
was well established in the U.S. It had bought Ansco in 1926
and had holdings of DuPont chemical and other U.S.
companies. See the history of I.G.Farben for more and for
the Nazi connections of these companies.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
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