- Part 1 - Part 2 - Part 3 - Part 4 - Part 5 -
CHAPTER XIX. WHY FISHING HOOK GREEN?
Once, about seven years ago, on the forum, someone under the nickname Black Glimmung turned to me:
- Could you try to objectively figure out what the artifact is in one of the A-17 images:
Figure: XIX-1. One of the images from the Apollo 17 mission.
As the brightness increased, short green lines appeared in the shadow of the stone (Figure XX-2).
Fig. XIX-2. Fragment of a photograph showing the location of the artifact (left) and the same fragment with increasing brightness (right).
In response, I wrote the following:
Promotional video:
The light-sensitive layers on the reversible film are arranged as follows - see Fig. XX-3. Above is a blue-sensitive layer (numbered 1), after exposure and processing, a yellow dye is formed in it. Number 2 is a yellow filter layer, which discolors during bleaching and fixing, 3 is a green-sensitive layer, a purple dye is formed in it, 4 - a red-sensitive layer after exposure and processing gives out a cyan dye, 5 - an antihalos layer - is removed during processing (remains empty gelatinous layer), 6 - transparent base, about 8 times thicker than all layers combined.
Fig. XIX-3. The structure of reversible color film: a) - before exposure, in the emulsion layers there is a light-sensitive substance (triangles), b) - after exposure and processing, dyes are formed.
The emulsion layers are very thin, a few microns thick, and although they are well hardened, the film must still be handled with great care. If a scratch passes over the emulsion, the yellow dye is removed first, which gives the scratch a blue tint (the remaining magenta dye + cyan). A deeper scratch causes the top two layers - two dyes - yellow and magenta - to be removed, leaving only cyan on the film. Therefore, emulsion scratches on reversible film are either blue or light blue - Fig. XIX-4.
Fig. XIX-4a. Scratches on the reversing film are blue, 6x6 cm slides.
Fig. XIX-4b (gif). Scratches on the reversing film are blue, 6x6 cm slides.
Films of high sensitivity - negative and reversal (slide film, reversal film), have the same arrangement of dyes as the light passes: yellow - magenta and cyan. Dyes are located quite differently on insensitive positive materials - photographic papers and positive films (print films). In the manufacture of these materials, the peculiarity of human vision was taken into account, the fact that the yellow dye practically does not carry information about the sharpness (Fig. XX-5).
Figure: XIX-5. Of the three dyes, yellow has the smallest information capacity.
If the information about the sharpness that all three dyes create is taken as 100%, then only 10% is yellow. But what happens during exposure? The emulsion layers themselves (before development) are a highly turbid medium, they strongly scatter light. Therefore, in the upper layer, the highest resolution is found (sharpness is best), and in the lowest, the resolution (in lines per millimeter) is one and a half to two times lower due to light scattering. With the classical arrangement of dyes (w-p-d), the maximum resolution falls on the yellow dye, and the eye sees practically nothing there - it does not see any small details. In this regard, the Kodak company in the mid-50s. The twentieth century released films with displaced layers: the yellow dye went to the very bottom.
The group that developed colored photographic papers believed that the greatest information capacity was carried by the cyan dye, so they put it at the very top. If we take scissors and begin to carefully scrape off the emulsion from the color photograph, we will see that the cyan dye will be removed first, and the scratches in this place will be red - these are two other dyes - magenta and yellow (Figure XX-6).
Fig. XIX-6. When scraping the emulsion on photographic paper, the blue dye is first removed, making the scratches red.
With further scraping, a yellow dye is visible at the bottom - Fig. XIX-7.
Fig. XIX-7. Sequential scraping of dyes on photographic paper (cyan - magenta - yellow).
Another development team working on film-based materials found that magenta dye was more informative than cyan because the absorption curve of magenta dye was most similar to the eye's visibility curve. It is because of this that the developers put a purple dye upstairs. All positive films, such as Eastman Print Film 5381, or modern Kodak 2383 film, have magenta dye on top. And for many years the soundtrack was only recorded in the upper emulsion layer to improve sharpness. In the middle of the processing process, after bleaching, the sound track was additionally processed with a black-and-white developer, as a result of which a silver image was formed in the same layer, dark-black, like on black-and-white film. This soundtrack (black and white track + magenta paint) looked dark purple and was called high magenta (Figure XX-8).
Fig. XIX-8. The stereo sound track (left) is dark purple.
Then there is a link to an article, from which you can find out why the sound track was additionally processed with a black and white developer, and how the color of the sound track changed over the last 80 years of the existence of color cinema. About the color of the audio track.
If at the beginning of a sound film, the light of an incandescent lamp was directed to the sound track (it was similar in size to a lamp in the sidelight of a car), then by 2005 a red laser was used instead of a lamp, and the sound track began to consist of a color opposite to red - from blue dye. The arrangement of dyes on the Kodak positive color has not changed since the mid-50s. XX century. If we start scratching the film positive, the scratches will turn out to be yellow-green (Fig. XX-9).
Figure: XIX-9a. Emulsion scratches on positive film look green.
Figure: XIX-9b (gif). Emulsion scratches on positive film look green.
Since
Video file: Colored scratches on slide, photographic paper and film positive.
By the way, on those slides that were found in the box, there are scratches on a dark background, and they are green (Fig. XX-10).
Fig. XIX-10. Green scratch near perforations.
All this testifies to the fact that before us is an image not on reversible, but on positive film. And this is not a slide, but a positive film. And since the film is positive, the image was printed from the negative. And this cannot be the original in any way, since this is the most common copy, obtained by a two-stage "negative-positive" method.
CHAPTER XX. HOW DOES SLIDE FILM DIFFER FROM POSITIVE?
On slide and positive film, the same images are visually obtained - positive. This leads to the fact that most people call slide film positive, although there is an unambiguous indication of its type on the packaging of the film. On POSITIVE films there is an indication that this film is intended for printing - color print film - fig. XX-1. This film is printed from the negative.
Figure XX-1. 600-meter box and label of modern color positive Kodak film.
The following is written on the slide films: “for color slides” (ie for color slides) - pic XX-2 or “for color transparencies” (for transparent color images) with the addition of “reversal film” - pic. XX-3.
Figure XX-2. Photographic film * Kodak Ektachrom * for color slides.
Figure XX-3. There is an indication on the package that this is reversal film and that it is intended for daylight shooting, 5500K.
For large unwinds, for example, 122 meters (that's 400 feet), the film is delivered in tin boxes. The label indicates in large letters that it is reversal film - Figure XX-4.
Figure XX-4. A 122 meter (400 ft) reversible film box.
In the identification number 7266 the number “7” means that this is a NARROW film, 16 mm wide; in the case of 35mm film, the number “5” would be the first. The second digit, “2”, is assigned to negative and reversible films; immediately there is an indication that this is not a positive film. For positive materials, the number “3” is in second place (for example, modern positive film 2383 or 5381 in the 60-70s of the XX century). And “66” is a modification of the film, and this number may change, for example, 8-10 years after any improvement in color rendition has been made in this type of film or when the structure of emulsion grains is changed. For example, now the Kodak company produces circulating films with the index “80” - 7280. At the same time, the first two digits remain unchanged, “7” and “2”, and the packaging still indicates that this is “Ektahrom” film - fig. XX -4.
Figure XX-4. Modern reversible film, 8 mm wide (type 7280).
The letter "T" in the name of the film "64T" indicates that the film is balanced for the light of incandescent lamps (3200 K). "T" is the first letter of the word tungsten - tungsten - an incandescent lamp glows by heating a tungsten coil. There is a table on the box that indicates that with an incandescent lamp (a household lamp is drawn), the filter is not installed, and in daylight (sun drawing), an orange W-85B filter is required (W is the catalog number of Retten, Wratten).
Positive cinematographic films are very different from reversible ones and cannot be replaced with one another. This is primarily due to the area of their use. Reversible materials are used for filming and must have a high sensitivity. For example, for filming in sunny weather, films with a low light sensitivity, 64 ASA units, are used, and for interiors and premises Kodak produces high sensitivity films, from 400 (Fig. XX-5) to 1600 units (Fig. XX-6).
Figure XX-5. Reversible film 400 units.
Figure: XX-6. Highly sensitive reversible film of 1600 units.
The situation is completely different with positive materials. Nobody loads them into the camera. Positive materials are imprinted with an image from the negative, like on photographic paper, and this happens in the laboratory. Copying from a negative does not take place in the dark, but under special laboratory lighting - under very weak yellow-green or yellow-orange lighting (Figure XX-7).
Figure XX-7. Lighting in the copy department when working with color positive films.
The copier has luminous panels so that you can read the order number, prefilter values and other service information, in addition, the buttons "start", "stop", "reverse", film speed indicators, image lamp voltage regulators and sound track lamps are highlighted etc. (Figure XX-8).
Figure XX-8. A modern cinematographer for 35 mm film.
At the same time, the copier must not only monitor the work of the copier, observing the process, but must constantly (every 15-20 minutes) change the printed positive roll for a new unexposed roll, install negative clips of another order, etc. … All this must be seen by the copier, and positive film should not be illuminated for at least 15 (or 30) minutes under a laboratory light. Therefore, positive film must have very low light sensitivity. For example, the sensitivity of the red layer of positive is about 10,000 times less than the sensitivity of a similar layer of reversible film for interiors - compare 0.04 and 400 ASA).
To expose such insensitive film, copiers use high-power incandescent lamps, such as 1200 watts (Figure XX-9).
Figure: XX-9. A burned out incandescent lamp of a film copier with a capacity of 1200 watts.
So, the main difference between positive films and slide films is that they are all very low sensitivity, the maximum sensitivity (for the blue layer) never exceeds one and a half units, while the sensitivity for the red layer is 20-40 times lower than that of the blue layer.
The second difference is the light conditions in which light-sensitive materials operate. Slide films are most often balanced for daylight (5500 K), approximately the same spectral composition is given by the light of a photo flash. Since daylight is close to EQUAL ENERGY white light, all three layers of reversing film must have the same sensitivity, and a lens filter is not required for daytime photography.
Now, if we talk about the color balance of positive films and colored photographic papers, then the color temperature at which they are balanced (films and colored photographic papers) is difficult to evaluate in one word or one meaning. On the one hand, the copier contains an incandescent lamp, but this leads to a hasty and erroneous conclusion that positive materials are supposedly balanced under an incandescent lamp with a color temperature of 2800-3200K. This is not true. Before getting on positive film, the light from the lamp passes through the negative, and all negatives are masked, they are orange-brown. This mask is visually similar (but slightly darker) to the W-85B type shooting filter, which lowers the color temperature from 5500 K to 3200 K. If such a filter is now installed in front of the incandescent lamp of the copier,then the color temperature will drop from 3200 K to about 2200 K. But that's not all. To balance the color positive film in layers (normalization of positive film), a peach light prefilter is installed in the light path, which further lowers the color temperature, to about 1900 K. Here is the lowest color temperature value for which color positive films are balanced. So if someone wants to shoot positive film in sunny weather, having loaded it into the camera, he will have to put at least two orange W-85B filters in front of the lens and set the shutter speed for about 1 second.which further lowers the color temperature to about 1900 K. This is the lowest color temperature value that color positive films are balanced to. So if someone wants to shoot positive film in sunny weather, having loaded it into the camera, he will have to put at least two orange W-85B filters in front of the lens and set the shutter speed for about 1 second.which further lowers the color temperature to about 1900 K. This is the lowest color temperature value that color positive films are balanced to. So if someone wants to shoot positive film in sunny weather, having loaded it into the camera, he will have to put at least two orange W-85B filters in front of the lens and set the shutter speed for about 1 second.
The third difference is the location of the light-sensitive layers. Slide film has the traditional arrangement of dyes in layers: yellow-magenta-cyan (from top to bottom), and positive has displaced layers: magenta dye on top, then cyan, and yellow at the bottom.
And, of course, there is one more fundamental difference - different processing processes. For positive films, this is the ECP-2D process (see label in Figure XX-1), and for slides, it is E-6 (see Figure XX-3 or XX-4). These processes are completely different from each other.
Whatever film we take, black and white or color, negative, slide or positive (including photographic paper), in all these materials, silver salts are a sensitive substance - silver chloride, iodide or bromide silver. But all materials (negative, positive, reversible) have different processing processes.
The process of processing black-and-white negatives and photographic papers is more or less clear. After exposure of black and white material, film and photographic paper are first developed. In this case, a part of the photosensitive substance, on which the light falls, darkens in the developer (the silver salt turns into fine-grained metallic silver), and a part of the photosensitive substance remains unused. So that it (the remaining light-sensitive substance) does not shine, it is removed from the film using a fixer. Ammonium thiosulfate, which is part of the fixer (previously it was sodium thiosulfate), dissolves silver salts, and they go into solution. Silver salts accumulate in the fixer, therefore, in large enterprises, no one pours fixers down the drain, up to 5 g of silver can be extracted from each liter of used fixer (by electrolysis). After fixing, the film is washed and dried. The final image on black and white negatives and on black and white photographic papers consists of fine silver, it looks black.
But the final image on colored materials consists of dyes. Since the dyes themselves are not light-sensitive, silver salts are still used as light-sensitive substances in all colored materials. But silver salts during development can only turn into silver (black), and they give a black and white image. Therefore, in the process of developing a colored material, in addition to a color image, a black and white image is necessarily formed from dyes in the emulsion layers, which we do not need. In connection with this color processes, a new stage is introduced - bleaching - the process of removing a black and white silver image. For example, this is how the process of processing a color negative, which is called C-41, looks like: Development - Whitening - Fixation - Stabilization - Fig. XX-10.
Figure XX-10. The sequence of stages in the C-41 process (processing of color photonegative).
During color development, the illuminated silver salts turn into silver, and clouds of dyes appear around these grains, which repeat the forms of microcrystals, therefore, in the emulsion layers during the development process, two images are formed at once: one is black and white, made of silver, and the second is color. from dyes.
In the next stage, in bleach, the black and white image disappears, it turns into a silver salt. And silver salts dissolve in the fixer. Due to the fact that after bleaching there is fixation, the black and white image is completely removed from the film, only dyes remain in the layers, which form the color image. Naturally, fixation also removes the unexposed photosensitive substance by dissolving it. After fixing, the film is washed in a stabilizer (water + formalin or water + dichloroisocyanuric acid, something like bleach) and dried.
The process of processing color positive film is fundamentally the same as that of color negative (C-41), only after each stage of processing is added washing. But in principle, the essence of the stages of color positive processing is exactly the same: first, in the color developer (in the places of exposure), two images are formed simultaneously, black and white and color, then with the help of bleaching the black and white silver image is removed, and in the fixer it is removed from the film … The fixer also dissolves the unused light-sensitive layers of the silver salt, and by the end of the treatment, only dyes remain inside the gelatinous layers.
The ECP-2D processing process, which is shown on the Kodak website, will seem a bit overwhelming at first. It contains options for processing positive film for three different types of bleaches, and also mentions additional stages associated with separate processing of the soundtrack, etc.
The intricacy of the processing arises from the need to amplify the audio track. But since you saw that there is no sound track on the 70-mm film, where the "moon shots" are depicted, we consider the issue of discussing various options for additional sound processing not fundamental and unnecessary in the stages of processing color positive film in our presentation. We still tend to believe that NASA used a negative-positive process to obtain a 70mm positive image, which involved copying the negative onto insensitive positive film instead of filming it onto slide film with a reversal process.
Chapter XXI. HOW DOES THE REFERRAL PROCESS GO?
The conversion process is fundamentally different from the processing of negative and positive. This process is familiar to many film amateurs of the older generation, because the shooting of family chronicles and amateur films was previously carried out exclusively by an inverted process.
The two-step, negative-positive process was too expensive and cumbersome for the filmmaker. After all, in order to see his “home” film on the screen, using a two-stage process, the film enthusiast first had to shoot and process the negative. Then this negative must be printed onto another film, positive, using a special copier. This second film must be processed in a different developer, according to a different recipe, and only then a positive image is obtained. In order to work on a two-stage process, a film enthusiast, in addition to a film projector, had to purchase a copier, and each film would then consist of two films - negative and positive.
Using the reversible film and the corresponding processing process, the amateur filmmaker immediately received a positive image, only in a single copy. But it didn't require a copier and two different processing processes. And instead of two (negative and positive), it was necessary to buy only one film - reversible.
Those who first begin their acquaintance with the reversible process are very surprised to learn that in the middle of the processing process the film is exposed to a bright light, illuminated, and then reappears, and that during machine processing under the cover of the developing machine there is a fluorescent lamp for exposing the film.
Let's take a closer look at the principle of the process. Let's start with a black and white material.
First, as usual, the object (Figure XXI-1) is filmed with a camera.
Figure XXI-1. Shooting an object.
Those who took out a sheet of photographic paper from a black bag and brought it out into the light know that the light-sensitive substance itself (silver salt) has a milky yellow tint. When exposed to light, a latent image appears in the light-sensitive emulsion layer (Figure XXI-2).
Figure XXI-2. Latent image after exposure.
Due to the development, the latent image is magnified millions of times and a visible image, a negative, is obtained (Fig. XXI-3).
Figure XXI-3. Image negative.
Where the most light falls on the surface of the material, there is more silver formed, and these places, which are light in the object, turn out to be the darkest after development. Not all of the light-sensitive substance in the emulsion has reacted. Where there were dark places in the subject that reflected little light, for example, hair, there in the negative the photosensitive substance (yellowish tint) remained almost intact. The fixer, which is usually applied after development, just dissolves these unreacted areas with silver salts. But no fixer is used in the bleaching process.
Instead, the negative is rinsed and dipped in bleach. The main ingredient in the bleach is red blood salt (iron-cyanide potassium) or potassium dichromate (chromic peak). These substances give the bleach a bright yellow color (in the first case) or bright orange in the case of a chromic peak. Bleach eats away at silver, the black color disappears, the negative is removed.
This is followed by a clarification stage that removes the yellow-orange cast. At this point, the image looks something like this - fig. XXI-4.
Figure XXI-4. Image after bleaching, negative image removed.
Places that were dark in the negative become almost transparent, and in unexposed places, a light-sensitive substance remains - a yellowish silver salt.
After bleaching, operations are performed in the light. First, the material is exposed for 1-2 minutes, and then the film is dipped into the developer. This is called the second manifestation. The highlighted silver salt in the developer quickly darkens, we see that the girl's hair is almost black. The image is reversed. The result is a positive (Figure XXI-5).
Figure XXI-5. Formation of a positive image after the second development.
By this time, all the light-sensitive substance contained in the emulsion layers is consumed: part of the substance was used to build a negative image, the rest of the substance, reduced to silver, creates a positive image. And in principle, there is nothing more to record. Therefore, many film enthusiasts did not use a fixer when they processed black and white reversible films at home, although it was included in the reagent kit for processing.
If we describe in words in stages the scheme for obtaining an inverted image, then it will turn out like this. First, after photographing, the image is developed and a negative is obtained. Only part of the light-sensitive substance is consumed for the formation of a negative. Then, with the help of bleach, the negative is completely removed, and the remaining photosensitive substance is illuminated and developed. As a result of the second manifestation, a positive is obtained.
The color treatment process is somewhat more complicated, but fundamentally remains the same. Likewise, at the first stage of development, a black and white negative image is formed, and the process is initially carried out in the dark. Part of the light-sensitive substance is spent on the construction of the negative. Then the film is exposed to light, and after exposure, the material is developed in a color developer. At this stage, two images are formed at once - a positive one from silver, i.e. black and white, and positive image from dyes, color. The bleach then dissolves all the black and white silver images, and in the fixer they go into solution. Only the positive image dyes remain (Figure XXI-6).
Figure XXI-6. The process of processing color reversible film.
Flare was in the process of E-4 orbital, but in the mid-60s. In the 20th century, during the E-6 process, the exposure was replaced by a tin chloride chemical treatment bath.
More details on the process of color circulation can be found in A. Redko's book "Fundamentals of photographic processes" (pages 345-351 of the book).
Chapter XXII. WHY DOES BLACK SPACE BECOME GREEN?
In 2005, the lunar images were re-scanned at high resolution (1800 dpi) and were posted on the Internet “for all mankind”.
On Flicker, you can find scanned originals unprocessed in “levels”, and here's the strange thing: in all these frames, the black space has turned green.
This is especially striking if there is a black border nearby.
Figure XXII-1. Black space looks dark green.
And this is not a single shot, this is a rule. This is a trend that seems inexplicable at first glance. Deep black space looks dark green, and this is clearly not a marriage of photographic film (Figure XXII-2).
Figure XXII-2. Black space looks dark green in almost all frames.
Continued: Part 7
Author: Leonid Konovalov