Alan Marcus

Early black & white films were only sensitive to blue light. As such blue objects recorded too dark on the film, thus too light on the print paper. Further, red cheeks and lips reproduce, on the print too dark, may be black. Blue sky appeared too light on the print thus white clouds will not stand out against a blue sky. (All changed when Vogel, Professor of Photography at Berlin Technical. Trying to solve a problem called an halation, he dyed film emulsions yellow. This trick worked plus the dye somehow forced the film emulsion to become sensitive to green light. This film, called orthochromatic, greatly improved the ability of films to realistically image-colored objects. Vogel, and his graduate students experimented with other dyes and films sensitive to red, green, and blue, called panchromatic, resulted. Still, blue sky reproduces as light gray. Clouds illumined by sunlight also reproduce light gray. Mounting a yellow filter, blocks some of the blue light of the sky. Thus blue sky reproduces darker. When so imaged, white clouds are caused to stand-out (added contrast) as they reproduce light gray against a darker gray sky.

The clear area of the SLR focusing screen works without a grid or mark. This is because focus is achieved when the apex of the rays formed by the camera lens kiss off with the apex of the rays from the eyepiece lens. In the case of the SLR it is fixed i.e. the apex of the rays produced by the eyepiece lens kiss off on the surface (image plane) of the view screen. In most applications, a mark on this surface is a requirement. Additionally the power of the eyepiece lens creates a shallow depth-of-focus.

The camera lens images by projecting a image of the outside world onto film or digital imaging chip. Most cameras are equipped with some method that allows the photographer to preview this image for purposes of composition and focusing. This projected image is an “aerial” image. An “aerial” image can only be seen if it somehow made visible. Traditionally we view this image by intercepting it using a flat glass surface that has been toughed-up. In other words, one surface is ground using an abrasive. This “ground” glass textured surface yields a viable image that is dim, inverted literally reversed and vignetted. One could substitute tissue paper to preform this task. For most camera applications, the ground glass viewing screen is supplemented using a flat Fresnel lens. This lens consists of concentric circles etched on its surface that form a lens-like effect. The Fresnel reduces the vignette and brightens the image. Because the Fresnel interferes with image acuity, generally it is excluded from the central portion of the viewing screen. In other words, the central area is plain ground glass. To improve the ability of the vies scene to perform and assist as a focusing aid, various additional schemes are employed. Often the center at the center of the view screen is a double prism array that yields a split image when focusing is amiss. This scheme works OK when the lens is not an extreme wide-angle or telephoto. To augment focusing a “microprism” is provided. This system works best at small apertures. Most common is a view screen incorporating several techniques. The view scene can even be clear flat glass. Light rays from the camera lens traverse the clear screen area. A strong magnifier, such as the eyepiece lens of the camera, intercepts these rays. Thus, the camera lens and the eyepiece lens, together works much like a microscope / telescope system. In other words, the clear screen area together with the eyepiece lens preforms to allow precise focusing.

Outdated paper that is spoiled or safelight not safe. Test safelight--- Place a piece of unexposed photo paper on your enlarger baseboard or work area under safelight conditions. Place 15 coins on the paper. Using a timer, remove a coin every 15 seconds. When all the coins are removed, quickly develop this paper, I suggest 120 seconds developing time. Stop and fix this paper according to your normal routine. Now examine the paper. You will see circular shadowgraphs where the coins were place. You will see that each has a different degree of blacking. From this pattern, you can determine if your safelight is truly safe and how long the paper will tolerate being exposed to the safelight.

The typical slide film displays 256:1 tonal range (if properly exposed and processed), A copy slide has a compressed tonal range, about 1 f-stop less = 128:1. Copy side film helps as does inter-negative film. We often made a copy as a color negative on this film. Then we exposed this negative on special film, similar to motion picture release film. Cine films were often shot using a color negative film and then printed for theater release. Since the life of a theater print film was short, a theater would order several copies. .

Once upon a time -- It was common practice to drag-out the slide projector. The same applies to movie film. Color prints on paper were possible but expensive. There were many reasons to duplicate slides and movies. We photofinisher's had special devices to do this task. It was good business. However, making the duplicates look exactly like the original was impossible. Most times, the duplicate picked up contrast due to a loss of scale. It was a chore to set-up these machines and thus the cost was high. m Kodak would make prints from slides. They were made on a special Kodachrome film with a white base. They were exposed in a special camera and developed in a Kodachrome processing machine. As time went by, a reversal color paper was available. The output was good. The cost was under a dollar a print for a 3 1/2 by 5 1/4 inch print. Professionals made slide shows of cities and popular attractions and these were sold en mass at tourist shops. Also schools were a market for professionally made educational stuff. Look up slide strip shows, a special projector that accepted 35mm film un-cut.

OK – You are being overly cautious. Don’t worry about the pour time. The 8 minutes + developing time allows adequate time to cancel out timing irregularities. In other words, pour time is only a worry when the wet-time is super short. Don’t worry about protecting any of the fluids from contact with the air during the processing cycle. All of the fluids of the process contain agents that retard aerial oxidation plus goodies that neutralize staining agents that result from aerial oxidation. Do pay attention to aerial oxidation when storing fluids between sessions. Plastic bottles that squeeze are best as you can squeeze to expel trapped air. Other techniques, add marbles to displace air. Another technique is adding a floating lid or floating stars made for this purpose. It is a good idea to keep all fluids of the process the same temperature. Pictorial film is made by applying many coats of emulsion and other over and under coats. Each likely will expand or contract at different rates. This can lead to excessive curling or if the temperature differences are extreme, the emulsion can crack like broken glass (reticulation). So we try and keep all fluids, including water rinse / wash ± 2° F. Many people like to use distilled water when mixing chemicals. I personally use tap water because I know that prepared formulas contain extra chemicals to combat tap water contaminates. Besides, distilled water in “hungry water” and it can over react, sometimes. As to drying: Film is made from gelatin. This stuff is the binder (glue) that holds the emulsion to the transparent film. Gelatin swells when wet and shrinks as it dries. We wash or otherwise purge the finished film of all residual chemicals. The last step is a wetting agent. This breaks up the surface tension of water thus mitigating its tendency to form water droplets. I squeegee to make sure no droplets remain. If they are present, they retard drying in that area. This causes microscopic differences in film thickness. The result is water-spots. Some think they are due to residual minerals however, most are thickness differences that are irreversible. Best advice, your first rolls should be test rolls void of valuable content. Practice makes perfect.

Several typos paper grade 2 not 1 is "normal" contrast.

Graphing film to see how it responds to exposure and development was pioneered by Ferdinand Hurter and Charles Driffield who published 1890. These gentleman are the founders of what is called the H&D curve. Scientist of that era relied on the slide rule, there was no computers or calculators. The slide rule is based on substation of addition and subtraction of logarithms (log notation) to multiply and divide (to name a few applications). The H&D graph is thus based on graph paper with logarithmic ruling. Ansel Adams applied the H&D characteristic curve when he and Fred Archer devised and published the “Zone System”. It is proper form, film is procession exposed in ½ stop increments and the yield is maximum black thru minimum density, usually 21 induvial levels of exposure. The backing (density) of each step is measured using a transmission densitometer and then grafted on logarithmic ruled paper. The log ruling is required because after the thirteen or fourteen step the exposing energy is 8,192 times the first. Using ordinary linear graph paper would make the graph yards long. In other words logarithmic graphing base 10 makes the graph practical and I think, elegant. The real increment of the graph is the f-stop. This is a 2x change in exposing energy. In other words, up the exposure 1 f-stop doubles the light energy, 1 f-stop down, half’s the exposing energy. The key value here is 2 (double or half). In log notion the value 2 is written is 10^0.30 (ten elevated to the 0.3 power). This is key to understating the plot because 1 f-stop = 30 units of density, 2 f-stops = 60 density units, 3 f-stops = 90d, 4 f-stop = 1.20d (each f-stop = 0.30 density delta because 2 in ordinary numbers = 10^.30 in log base 10 notion. OK, keep in mind, 30 density units = 1 f-stop (this is a truism): But --- Thru only on the straight line of the H&D graph (region of film latitude). Also true only if the straight line goes upward at a 45° angle. Now the contrast of the photo material is measured by this angle. We take a protractor and measure the angle of this straight line. Then we use a trigonometry table and find the tangent of this angle (TAN). A 45° angle has a TAN of 1. If the TAN is 1, the angle is 45° and 1 f-stop has a delta of 30 units of density. The TAN of this straight line is, in the jargon of photography “GAMMA”. Now comes the massage: A straight line slope angle, GAMMA 1 has been proven to be too contrasty for pictorial photography. Typically a negative that prints on grade 2 photo papers is considered to have “normal” contrast. For technical reason beyond the scope of this expiation, the slope of the straight line of a pictorial film is likely set to a GAMMA of 0.8 = 38 ½ °. Now the negative fits nicely on #2 grade paper however 1 f-stop no longer = 30 density units. This GAMMA .8 slope means 30 x 0.8 = 24. If you are following me, a GAMMA of .8 translates to 1 f-stop delta = 24 density units (not 30). Bottom line: We adjust GAMMA via developer choice and time and temperature. When we uses these adjusters, we modify the delta ((count of the density units per 1 f-stop increment. If this is confusing to you, I have been studying this stuff for 50+ years and its remains gobbledygook ! As to the H&D graph: We divide this plot into regions: The region of under-exposure (toe). Region of film latitude (slight-line). The region of over-exposure (shoulder). The curve switches to a downward direction (region of solorization). One key to understand the implications of this curve is to measure, with protractor, the angle of the stright line. Most pictoral films will measure about 36° (slope angle). For the moment assume 45°. We find the angle and using a trig table, fine the Tan of this angle. The Tan of a 45° = 1. Note, this is a log (logarithmic) graft. Also note, the f-stop is the common unit of exposure. This unit increments 2X i.e. each f-stop increment constitutes a doubling or halfling of exposing energy. In log units base 10, a doubling of halfling = a delta of 10^0.30. In other words, if we up the exposure 1 f-stop, we expect the graphed density to clime 0.30 denity units. Conversely, if we lower the exposure 1 f-stop, we expect the density to decrease 0.30. Now this happens only on the stright line, and only if the slope angle is 45°. By the way, the Tan of the straight line is called “Gamma” Thus we aret talking a film with a Gamma of 1. Now pictorial films are deemed too contrast if they have a Gamma of 1. Mainly this is due to the the fact that a grade 2 printing paper is considered “normal” as to contrast. Also, in log notations base 10 a Gamma of 1 = a stright line angle of 45°. Since log 0.30 = 2 this means a 1 f=top delta translates to a density change of 30 units of density = 1 f-stop. Because pictoral films are adjusted to yield “normal” contest on grade 2 paper, The typical pictorial film has its straight line depressed to a Gamma = 0.80 (an angle of 38°). This translates to: 1 f-stop alters the density of Gamma .8 film = 0.30 X .8 = 0.24 density units. In other words the typical pictorial film responds to exposure change with a delta of 24 density units.

The astronomical crowd considers 50mm to be magnification 1. This is arguable!. If you accept this (I do), then mounting a100mm delivers 2X and a 500mm delivers 500 ÷ 50 = 10X. I have pondered this rule of thumb and I discovered it is based on a 50mm lens mounted on a 35mm film camera. The dimensions of the film frame are 24mm by 36mm with a diagonal of 43.3mm. The photographic community rounds this value up to 50mm. The basis of this rule-of-thumb is: Magnification 1 occurs when you mount a lens with a focal length that is approximately the same as the diagonal measure. Now you should know that the photographic crowd considers a 50mm mounted on a 35mm film camera delivers a “normal” perspective -- thus the 50mm is a “normal” lens. Actually, mounting a lens with a focal length equal to the diagonal measure of the film frame or digital sensor, delivers “normal”. Such a lash-up delivers a 45° angle of view, camera held horizontal (landscape). Find the specifications for your camera’s imaging chip and calculate the diagonal measure of this rectangle. Mount a lens with this focal length and call it magnification 1. As an example: Your camera is a Lumix G7. . This format measures 13mm height by 17.3 mm length. The diagonal measure of this rectangle is approximately 21.64mm. If you mount a 300m lens, the magnification delivered is 300 ÷ 21.64 = 14X. OK for this math: Now the rest of the story – Your camera sports a miniature size sensor; thus the resulting image is practically worthless unless magnified. You view this image on a computer screen or you make a paper print. Both will be enlargements. You must take into account the degree of magnification applied to the final image to be viewed. Find a target of known length. An automobile will do; just measure its length. Now step away and shoot pictures. You can use your zoom or fixed focal lengths. As you shoot, record the camera’s focal length and your distance to the subject. Procure a clear plastic ruler. Display the images of the cars on your computer screen. Divide the length of the car’s image on the screen into the known length of the car. That math delivers the total magnification applied by the camera and the viewing method.

Why glossy paper is more contrasty: We view film, both negative and positive, by transmitted light. In other words we look at our negatives and slides by holding them up to a light or projecting them via light that traverses the material. The average difference, clear film to max density is about 1:1024. Since each f-stop is a 2x delta from the next, we are talking about a 10 f-stop dynamic range. We view prints on paper by reflected light. A nearby lamp plays light on the print we are viewing. This print’s surface reflects away some of this light. The remainder will transverse the print’s emulsion. As it travels, it encounters clumps of opaque metallic silver or, in the case of a color print, it encounters colored dye. In both cases, a reduced amount of light arrives at a white reflective coat, a primer that holds the gelatin emulsion to the paper. This primer layer has a name, it is “Baryta”. For years and years this nearly pure white coat is a suspension of barium sulfate. This stuff is now man made, originally a clay found in nature. Today it is laced with special dyes that have fluorescent brightening properties. When the light that is illuminating the print arrives at the Baryta, it has been modified considerably by obstructions suspended in the print’s emulsion. Now the enduring light rays reflect back into the print emulsion which they must traverse again. In other words, the image you are eyeing is formed by light that makes two transits. This fact allows the pint emulsion to be quite weak as compared to film emulsions, In other words print paper emulsion a made with far less silver and or dye than a film material, about the ½ the silver or dye on paper based emulsion. Now that the print viewing light has exited the print paper, this forms the image you see. If the print paper has super low gloss, you will see a contrast range of 1:32, that’s 5 f-stops. If the print has a high gloss, the contrast range will be 1:64 or about 6 f-stops. That’s the rest of the story – glossy paper is more contrasty!

Pictorial films (panchromatic emulsions) are not sensitive to radiations beyond the visible red, starts at 700nm. Infrared sensitivity is in the range of 700 to 900nm. In other words, hot objects emit IR within this range. We are talking about objects with temperatures 250 to 500°C (482 to 932°F). Because film and digital cameras are sensitive to light, when imaging you need to exclude. Best is a Wratten 87. However, depending on the desired effect you can use a dark red. Likely you have an IR TV remote. You can use this to make tests. If you focus on the business end of at IR remote, your camera will likely allow you view this emission. Now try filters you already have like, deep red or deep orange. Likely some extermination will find a good combination. You can even try cellophane candy or Xmas wrappings.

All lenses project a circular image. This image is best at the center as it degrades with distance from the axis. Since the central portion is best, its bounties contain what is called “the circle of good definition”. As a rule of thumb, we fit lenses to cameras and enlargers based on the corner-to-corner measure of the format. We are talking diagonal measure. For the 35mm format we choose a 50mm, for the 6cm by 6cm we choose a 75mm, for the 2 ¼ x 3 ¼ a 90mm and for the 4X5 a 150mm. Let me add, special wide-coverage lenses are available mainly in use for camera. The enlarger suffers because such wide-coverage projection lenses are rare. The problem is caused by the need to maintain a steep figure (curve of the lens) at its boundaries and what is called “cosign error”. The light from the projected image at the center is square but at the bounders of the projected image, the light hits the paper at a steep angle. Think about a flashlight beam shining on a wall, straight it makes a circle of light. At an angle, we get an ellipse of light. The ellipse has more surface area than the circle thus the light that plays on the ellipse is more feeble. The negative / positive process, negative film projected on to paper has an advantage over the vignette as compared to positive film projected onto positive paper. The camera vignettes, the enlarger lens vignettes. These tend to somewhat cancel. The vignette of camera lens on negative film is countered by the vignette of the enlarge lens and the result is a more uniform print. Conversely, when printing slide film on a reversal paper, the effects of the vignette, both camera and projector are additive. This is the worst case scenario.

A high gloss finish add about 1 contrast grade, maybe more. You will never need to experience the problems we had, in the early days, to achieve such a finish. All the photo labs that wanted glossy prints used a method called the ferrotype process. We used sheet metal plates, polished to a high gloss and then enameled, or chrome plated, or stainless steel. The well washed print was then squeegeed onto the plate using a rubber roller. In the photofinishing plant we had heated print dryers with giant chrome plated drums. We needed to keep the polish on these surfaces so we spent a lot of time cleaning and polishing. The print, once squeegeed on the plate could be air-dried or forced dried with heat. The problem was separating the print paper from the ferrotype plate. If not immaculately clean, the print would not self-separate. The only way to remove it was water and peel off, usually this destroyed the print. On the market were several pre-soak concoctions both for black & white and color prints. The winner was Pako of Minneapolis (PakoSol / PakoChrome). O’ the joy of RC paper (resin coated). The glossy version of this paper naturally air-dried to a high gloss, no ferrotyping needed.

Foot note: Years ago, I was Technical Manager Photofinishing for Eckerd Drugs. We operated 7 giant photofinishing labs in the South East USA. I was charged to build an 8th in Metairie. I finished the building but never built the lab due to environmental challenges posed by the city. The lab was to process and print 20,000 rolls of color film per day

Photo films work because the chemicals of the process are selective. The developer has the ability, in the time allotted, to differentiate between exposed and unexposed salts of silver. Subsequent, the developer reduces exposed silver salts to metallic silver and a halogen (Swedish for salt maker). The metallic silver component becomes the black and white image; the halogen is dissolved into the waters of the developer. As film ages more and more unexposed silver salts become developable. In other words, film over time film ages, its fog lever increases. Thus in time, all photo film expires. What I am trying to say, think twice before buying and imaging with outdated film. Now Kodachrome is basically three specialized black & white film emulsions coated on the same film support. As such this film could be developed in standard black & white chemicals. However, this material is fabricated to be developed in a rather complex series of chemical steps. This process resulted in a fine-looking full color image suitable for viewing by projection. The resulting color transparences were often re-imaged as prints on paper. Assuming the Kodachrome film you will use is still viable, you can expose it and process it in ordinary black & white chemistry. The result will be a black & white negative image. Your pitfall is, this color film was designed to be loaded into both still and movie cameras under subdued light. To protect the film roll from being fogged during the loading/unlading procedure, the back of this film has an opaque coat of lamp black. This is called a RemJet (removable jet black backing). Assuming you succeeded in the exposing and developing steps, you will have difficulty removing the RemJet. To remove the film is soaked in an alkaline solution such as sodium sulfite. This softens the binder that holds the RemJet to the film. Next the RemJet is buffed away with a soft cotton swab. Best of Luck

Often we are tasked to image rectangular and square objects. Consider a tall building. You and your camera are at street level. Because you are close, you must point your camera upwards to encompass the entire structure. The results will be an image of the building that converges at the top. This convergence contributes to the illusion of height but --- often in architectural photography, the requirement is an image that depicts a faultless rectangle. If we shoot from the middle floor of an adjacent building, our image shows converges at both top and bottom. Swing and tilt camera to the rescue. Another example, we are hired to shoot an ad for a breakfast cereal. The box is rectangular. Your view shows a perfect rectangle. To achieve you position the camera square with the box. The resulting image shows the box face but no sides or top (unsatisfactory). You shift the camera position to show the box face and top and side. Sorry to report, the box front will image as a parallelogram. Swings and tilts to the rescue. We use a camera position that images front, top and side. We correct the skewed image with swings and tilts. Professionals, who did this stuff for a living using film, used large format view cameras that featured excessive swings and tilts. Largely the film is held parallel to the object and the lens, free to move about and is positioned independently for best composition. Digital cameras with tilt lenses fall short of what a view camera can do

Camera viewfinders are more complicated than you might think. What we want is a way to preview the picture we are about to take with high accuracy. Now most pictures we take will come out OK even if the viewfinder view is tainted. This is a subject that has been worked on for years by the camera makers. The best solution involves using mirrors and prisms. Such a design known as a SLR (single lens reflex) allows the photographer to preview, almost exactly, what the camera will see, when the shutter is activated. The SLR design is optically and mechanically complex and this elevates the cost of the camera. A cost most serious photographers gladly pay in order to get preview accuracy. Now with the film camera, no one has been able to make much additional headway. The advent of digital photography has changed the viewfinder‘s scheme. The digital imagining chip allows the camera maker the opportunity to display to the photographer a worthy preview. Now purest still favor the SLR design but Keep in mind, digital photo technology is still in its infancy thus improvements are coming minute by minute. In the current digital camera design, a replica of what the camera sees is displayed on an LCD (Liquid Crystal Display). This image is far lower in resolution than the actual view presented to the camera’s image sensor. Additionally the color rendering of this preview image is substandard. There is great room for improvement. You need not worry, new previewing technology is forthcoming. Meanwhile, the previewing screen affords an opportunity to display a plethora of thing like; shutter speed, ISO, aperture, focal length, camera-to-subject distance, a preview of depth-of-field, time, date, not to mention computer based menus. The SLR was one the preferred, digital allows opportunity. Stick around, you haven’t seen anything yet!

If the problem is poor bleaching and fixing, the film can be re-bleached and re-fixed. You can do this yourself or as a lab to do this task The following may seem weird but the science is sound. Retained silver present in film will block infrared light. You can use an IR TV remote as an IR source and a digital camera as the receiver., to examine the film. Fist find a piece of film you think is OK and view it in the dark with your camera. Illuminate the film you are testing using the IR TV remote place behind the film You can test the ability of your camera to detect IR by peering at the operating TV remote with no film blocking the IR emitter in its nose.

An optical filter passes its color and and blocks its opposite. A yellow filter passes yellow light (red + green) and block blue light. We mount a yellow filter when using black & white film. Fluffy white clouds are embolden as the yellow filter darkens the blue sky. A red filter does this only stronger. A strong red + under-exposure give the illusion of night. A green filter lightens foliage. A UV filter cuts through distance haze. The UV is commonly used, not for its UV blocking, but to protect our precious lenses. A polarizing filter mitigates reflections from some surfaces.

This is the link to the US Government Guidance Document that covers photo effluent This is the bible on this subject. Guidance Document for the Control of Water Pollution in the Photographic Processing Industry

Once upon a time, Kodak Rochester had an environmental department. At the height of world concern over the effluent from giant photofinishing and motion picture processors, this was manned by some of the brightest minds. Most of my training came from their publications and seminars. The subject of home septic tanks came up many times. Privately they were conversed, no harm, no fowl. Publicly Kodak errs on the side of caution. Septic systems drain to streams and rivers thus the photo lab effluent should be hauled away via a licensed agency.

@ jose_angel No need to worry about the amount of fixer from a home darkroom. Yes it will slightly increase the amount of choline the sewer plant will need to use. They collineate by bubbling chlorine gas into the waters of the sewer treatment plant or a small plant will use chlorine tablets like a home swimming pool. In both cases they must achieve a Federal standard choline level in the released sewage. They cannot hold back this stuff as all plants have limited storage. If your fixer has any effect, it will be they need to add an extra tablet etc. As to the silver -- This depends on how they test their sludge. If they use nitric acid reagent, any silver sulfide in the sludge will test positive. Silver sulfide is inert but this test will give a false positive. If the stuff tests positive reducing its value as a fertilizer. but the silver content from a photo lab is still inert.

Disposing of spent photo chemicals: Not all that long ago, I was technical manager of 7 giant photofinishing labs (each 20,000 rolls a day) plus hundreds of in-store mini-labs. Photo chemical handling and disposal was a top priority. I had to become an “expert” so I went to school and became a registered environmental assessor. When it comes to dumping spent photo chemicals down the drain, there is myth and there is lore. Mostly the truth is ignored. For the most part, spent photo chemicals are pretty much benign. What I am saying is -- a home photo lab, disposing of spent chemicals down the drain doesn’t contribute more than a thimble full of harm. That’s because the harm is different from what is commonly believed. The real harm is BOD (biological oxygen demand) and COD (chemical oxygen demand). The home darkroom’s entire monthly discharge is miniscule. The waste we put down the drain, human and chemical, is treated by the municipal sewer system mainly by aeration followed by chlorination. The aeration handles the oxygen demand; the chlorination treats biohazards. The sewer treatment plant is supposed to cut the sewerage oxygen demand to zero. If not, the released sewerage continues to take on oxygen from the waters of streams, rivers, lakes and oceans. Aquatic life in these waters must then compete. If they fail to get their needed oxygen, they die. What I am alluding to – the problem of chemicals in the sewer system -- is their added oxygen demand. A small home darkroom will not have much impact. What will impact is large industrial photo labs and businesses like food processing and chemical manufacturing. Since the photo lab discharge is both acids and alkaline, the net balance of comingled chemical discharge is near neutral. Toxics, if any will become chemically inert within minutes of discharge. Silver, the main agent of discussion, converts to silver sulfite which is inert. Some forms of silver are toxic; the photo lab output is not in this category. What then is the real harm? The answer is the fixer! The fixer we use is the same stuff used by tropical fish enthusiasts to rid tap water of chlorine. If we dump barrels full of fixer down the drain, it arrives at the sewer plant and causes the chlorine they must add, to dissipate. Given this scenario, the sewer plant, which must release, will pass bio hazards to the environment. We, the photographic community wish to be good neighbors. We don’t want to be the source of harm. Let me assure you, your home darkroom’s discharge is not the culprit you think it is.

It seems too distinct to be a developing issue. Usually such effect is indistinct. If this effect was caused in the camera, it’s likely due to camera motion induced by too slow a shutter or perhaps optical flare or reflection. Or this could be external to the camera, occurring during scanning. If this is a developing issue, it most closely resembles “bromide drag”. However, bromide drag has an indicator. Look closely at the edge printing near and between the sprocket holes. These numbers, letters and symbols are photographically applied to the edges of the film. They are latent images that develop up just like objects in the scene you are imaging. Pay attention to dots. Bromide drag is identified by a comet-like tail streaking from one or more of the dots. What is bromide drag? The film emulsion consists of salts of silver imbedded in a binder of transparent gelatin. When the film is placed in the developer, being mostly water, it causes the gelatin to swell, much like a dry sponge plunged into water. This swelling allows the waters of the developer, containing the developing agents to enter. This fluid percolates about, does its work, and exits. This fluid exchange happens repeatedly while the film is in the solution. Agitation distributes fresh developer and at the same time swabs away spent developer. Spent developer is heavier than fresh. If agitation is scant, spent developer accumulates, particularly in areas of high exposure. Initially, this cloud of spent developer acts to prevent the entry of fresh solution. Additionally, this cloud of spent developer begins to drift downward under the influence of gravity. As this cloud drifts downward over locations of low exposure, its downward drift is the origin of ebb currents. These infinitesimally weak currents bring in fresh developer. The result is an elevated density in areas of clear film that is adjacent to areas of high exposure with lots of developer action. The countermeasure is routine but random agitation. In large photofinisher equipment, this agitation is accomplished by bubbling bursts of nitrogen gas via a distributer at the bottom of the tank.