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Newsgroups: rec.photo.darkroom, rec.arts.movies.tech, rec.arts.movies.production, alt.photography, aus.photo
From: "Richard Knoppow" <dickb...@ix.netcom.com>
Date: Tue, 12 May 2009 11:28:03 -0700
Local: Wed, May 13 2009 4:28 am
Subject: Re: Wavelength response of first type of film with sound?
news:4f5cd382-9b77-4cf0-a02c-de0733aba0e6@y34g2000prb.googlegroups.com...
> Hi: Nearly all films used for making photographic sound > What wavelengths of light specifically affect the type of > From what I know, most of the more modern films are > I'm thinking of a theoretical device using analog audio > I don't have much of an application here. I'm just in it > Thanks 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 dickb...@ix.netcom.com You must Sign in before you can post messages.
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