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Wavelength response of first type of film with sound?



 
 
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Old May 12th 09, 07:28 PM posted to rec.photo.darkroom,rec.arts.movies.tech,rec.arts.movies.production,alt.photography,aus.photo
Richard Knoppow
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Default Wavelength response of first type of film with sound?


"GreenXenon" wrote in message
...
Hi:

What wavelengths of light specifically affect the type of
film used in
the first movie containing an variable-density optical
audio track? I
am specifically interested in the chemical composition of
the optical
audio track.

From what I know, most of the more modern films are
unaffected by red
light.

I'm thinking of a theoretical device using analog audio
recording on
VD optical tracks containing the oldest film chemical
composition. The
source of light are multiple laser beams consisting of
wavelengths
that could record the audio onto the film. Each beam has a
different
wavelength. The beams are then mixed together to get a
single beam of
all the necessary wavelengths. The beam then shines onto
the film to
record the audio.

I don't have much of an application here. I'm just in it
for the
science.


Thanks


Nearly all films used for making photographic sound
negatives were blue sensitive (i.e., color blind). The main
difference between film for variable density and variable
width (AKA variable area) was the contrast. Variable density
recording requires low to medium contrast film and variable
width requires quite high contrast. The exact contrast is
determined by the film used for making the prints. That is
tests are made to find the best combination of exposure and
development of the sound negative to minimize distortion in
the final print. The contrast of the print when composite
prints are made (both picture and sound) is determined by
the picture so the print contrast is usually fixed and
requires the negative to match it.
One of the problems with both types of recording, but
especially for variable width recording, is image spread in
the emulsion. This is also called irradiation and is a
blurring of the image due to diffusion of light by the
emulsion. Modern films, which have much thinner emulsions
than those of perhaps fifty years ago, do not suffer as much
from irradiation but still have some. The idea of matching
the negative to the positive is partially to counteract the
image spread since the spread in the positive will correct
for that in the positive if exactly right.
Other methods were tried in the old days. For instance,
the use of ultra-violet lamps in the recorder were common in
the mid to late 1930s. This system does result in sharper
images since it confines exposure to the surface of the
emulsion, but the intensity of the lamps is marginal so
getting properly exposed negatives was difficult. Also tried
was using film with a yellow dye in the emulsion. This also
confined the exposure to the surface but had the same
problems with lack of enough light.
There are modern systems of photographic recording that
use beams of multiple colored lights as you suggest for
stereo. For the most part photographic recording is a thing
of the past. Magnetic recording replaced photographic
recording for original tracks beginning around 1948 and had
completely supplanted it by the mid 1950s. Photographic
tracks for release prints continues to some extent to the
present. They are economical to make and have long life.
However, for most theatrical release the sound is now on a
digital disc, so we have come full circle to the
sound-on-disc method use for the first commercial sound
pictures.
An excellent source for material on motion picture sound
is the archives of the _Journal of the Society of Motion
Picture and Television Engineers_ Larger library systems
probably have it. I don't know if the complete journals are
available on disc or on line. Nearly all developments in
motion picture sound recording and related topics such as
the improvement in film made for sound recording is to be
found in this journal.
As far as modern film, nearly all B&W film made now is
"panchromatic", that is sensitive to all visible colors.
Simple emulsions are sensitive only to blue and near
ultra-violet. By adding sensitizing dyes to the emulsion the
color sensitivity can be extended toward red.
"Orthochromatic" film is sensitive to blue, green, and some
yellow. Ortho film became available about the mid 'teens.
Panchromatic film became available about the early 1920's
but was not adopted by the motion picture industry until the
introduction of sound. Because the arc lighting equipment
common in motion picture production was mechanically noisy
sound recording precluded its use. The output of blue light
from incandescent lamps is much smaller than from arc lamps
so the orthochromatic film of the time was simply not
sensitive enough and a switch to panchromatic film had to be
made. This, in turn, required a change in the way sets were
painted, in makeup, in lighting, etc. However, the film used
in film recording machines was typically the same film used
for duplicating negatives (variable density) or for release
printing (for variable width)continued to be blue sensitive
only. These films continued to be used until specially made
sound recording films became available in about the mid
1930s.
--
Richard Knoppow
Los Angeles, CA, USA



 




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