[rollei_list] Re: Old film
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Mon, 30 May 2005 10:00:48 -0700
----- Original Message -----
From: "Thor Legvold" <tlegvold@xxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Monday, May 30, 2005 9:20 AM
Subject: [rollei_list] Re: Old film
>I still prefer Kodachrome for 35mm. A shame it's not
>available anymore
> for 120.
>
> Thor
I don't know why Kodak has been trying to kill off
Kodachrome but they have for a long time. Probably
supporting the special processing is the problem. Kodachrome
evidently has excellent dark storage properties while
Ektachrome type films have better resistance to fading under
projection. I've seen quite a lot of Kodachrome that still
looks pristine after 60 years. I am not sure why the dyes
are so stable. Kodachrome differs from more recent color
films in that the substances which form the dyes are in the
developing solutions rather than in the emulsion layers.
This may offer a wider range of dyes that can be used or,
perhaps its something to do with residues of some sort in
the emulsion layers.
Kodachrome has a curious history. From bits of history
gotten from various sources it seems that George Eastman got
interested in finding a practical color film for amateur
photographers. Its hinted that this desire was one reason
for the establishment of the Kodak Research Laboratories
although I think Eastman's aquaintance with the Edison lab,
which eventually became the famous General Electric research
lab, may have inspired its creation. Kodak was not
successful during Eastman's lifetime although it introduced
at least two early color processes. One was an additive
process using a reseau of colored particals similar to the
Dufycolor process. Agfa also had a commercial process using
a version of the same technique, as did others. Kodak called
its material Kodachrome. I no longer remember the date of
introduction but I think it was in the 1920's, perhaps even
earlier. It was not a sucessful process. The other earlier
Kodak system was called Kodacolor and was a lenticular
system for 16mm motion pictures. This was introduced in the
early 1930's. Lenticular color systems have some serious
inherent problems. One of the worst is color fringing of out
of focus areas of the image. The syetem also requires a lens
with a large physical aperture causing a limited depth of
field and an exageration of the above problem. A great deal
of work by Kodak in cooperation with Paramount Pictures was
put into adapting lenticular color for professional motion
pictures. The system works pretty well for reversal where
the camera original is projected but there are grave
difficulties in printing and duplicating. These, along with
the relatively poor image quality caused the system to be
unsuccessful and it was withdrawn after a relatively short
time.
The later process known as Kodachrome was introduced
about 1935 as a 16mm motion picture stock. The original
processing method was very complex and very fussy. It
depended on the conrolled penetration of a bleach into the
emulsion. The film was first developed into a negative. It
was then given a reversal development for the color nearest
the support. After this it was bleached in a bleach solution
that penetrated only the two top layers. Then it was again
developed in a developer which produced the right color for
the center layer. Again it was bleached, this time for the
top layer only. Then it was developed a third time for the
top layer. Joseph Friedman, in his book on the history of
color processes, attributes this method to Mannes and
Godowsky since other parts of the Kodachrome process dated
from the turn of the century and were fairly well known
technology. After about a year and half a better method of
processing was found. This is the method still used. This
still requires three separate reversal developments in
developer containing the right couplers for the particular
layers but eliminates the need for the differential
bleaching. It makes use of the color sensitizing of the red
layer, which remains after the first development so that
selective re-exposure of the three layers is possible. The
first reversal is of the bottom layer by fogging it with red
light from the support side. Since none of the other layers
is sensitive to red only the bottom layer becomes
developable. Next the top layer is fogged using blue light.
Because the yellow filter layer is intact the blue light
does not fog the center (green recording) layer. After the
top layer is developed the center layer is developed in a
fogging developer. All this was necessitated by Kodak's lack
of success in finding a way to keep dye couplers from
wandering from layer to layer. Agfa did find a way and
introduced a reversal color film at about the same time as
Kodachrome that could be developed in a much simpler
fashion. However, it was never sold in the US and was
inferior to Kodachrome in image quality. The Agfa method of
anchoring the dye is the one currently in use for all
chromogenic color films. Kodak did eventually find another
method of anchoring the couplers. This was introduced in
Kodacolor film c.1941 and was the basis for Kodak color
materials until probably the 1980's when they adopted the
Agfa method. It is reported that Kodak made materials for
the military using the Agfa technique during WW-2 when the
Agfa patents were seized by the government.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
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