does the developer time really effect the outcome of a picture?

[daniel_morelos]

<p>i know it affects the way the film out, but i don't know why!? you guys have been helping me a lot on here lately and i appreciate it! I just need some help on the math and science behind how developer times affect film! THANKS!</p>

[SCL]

<p>Simply because temperature affects the speed of chemical reactions. Additionally, temperature affects other things like reticulation. It isn't math you need, merely an understanding of chemical reactions.</p>

[bob_sunley]

<p>Pretty sure this question and answers that you can understand without a postgrad degree are in this thread and other sources referenced in this thread. <br>

http://www.photo.net/black-and-white-photo-film-processing-forum/00aAu1</p>

<p>esp the post at 8:34PM on March 23rd. :)</p>

<p> </p>

[SCL]

<p>I should have been more specific...in the world of chemical kinetics, as a general statement, increased temperature increases the speed of electron activity, hence ionic reactions...which means the process of developing occurs more quickly. This, of course makes certain assumptions, including the concentration of the chemicals and whether or not air pressure remains constant. It has other effects as well, but that is probably more complicated than you are seeking. The math is basic calculus, but rather extensive, based on whether you are merely seeking to compare rates of change related the variables, or you want to follow each stage of development with each causative factor.</p>

[andylynn]

<p>Think of a normal piece of B&W film. To put it very simply, it's a thin sheet of clear plastic coated with particles of silver halide. Silver halide is a material that reacts to light. It's in little bits that will later become the grain in the image, and they've been stuck to the film by mixing them into a gelatinous sort of gunk that sticks to the film and dries. It's kept in darkness as it's cut up into 35mm wide strips, as the sprocket holes are cut in the strips and as the strips are loaded into the cartridges that go in your camera.</p>

<p>Now you take a shot. The film is briefly exposed to light that's been focused into an image on it by the lens, as the shutter opens for whatever amount of time is needed to get the right amount of light in. You wind the film back into the cartridge and now it's in there, with the silver halide particles having been exposed to light, which has caused a chemical change in them because they react to light.</p>

<p>The function of the developer is (and I'm really simplifying here) to remove the halide from the silver halide, in the particles that have been exposed to light. This converts them to plain old silver. Whether this will happen to any particular particle is a function of how much light has hit it, how much of the developer reaction it's undergone, and some randomness. So your film now has scattered bits of regular silver, mixed in with the silver halide, and how dense the concentration of bits that have been converted, in any particular area, depends on how much light hit that area and how much developing reaction it got.</p>

<p>The developing reaction is a gradual process. The speed of the reaction depends on temperature - higher temperature means more energy in the system means faster reaction. For any given temperature there's some amount of time that gives the amount of reaction typically needed for that type of film.</p>

<p>The stop bath stops the developing reaction, and fixer dissolves silver halide particles but not plain silver particles. So what's left at the end is the silver particles that resulted from the developing reaction. Silver is opaque, so you shine a light through it and the particles cast a shadow. The more light hit some area of the film, the more silver it has, so the darker the shadow it casts - this is why it's a negative. The enlarger projects the pattern of shadows onto the photographic paper, which, conveniently, also works in negative (so it can reverse the image back to positive) and you're pretty much repeating the same process when you develop the paper.</p>

<p>Again, there's a lot I simplified or omitted (and there's a lot I don't know). If you want to know this for school it would be best to research it yourself!</p>

[chris_waller]

<p>There are three factors which affect development: time, temperature and agitation. More time, higher temperature and more agitation will all increase the degree of development and, at its most basic, will increase the contrast of the neg.</p>

<p>Your best bet is to get a good textbook such as 'Basic Photo Science' by Walls and Attridge.</p>

[Alan Marcus]

<p>The effect temperature plays on the developing process is complex. No need to tell you that development will take place at a more rapid pace if the temperature of the developer solution is increased.</p>

<p>From a chemist's viewpoint the obvious answer is, the higher the temperature the more rapidly the chemicals ionize or dissociate. However, this does not tell the tale.</p>

<p>The light sensitive salts of silver are crystals are held in place on film or paper by means of a binder. This glue like substance imbeds the silver crystals and holds them in place. Today this binder is purified gelatin. Gelatin is used because it has low solubility, highly flexible, transparent and most of all it is permeable.</p>

<p>The permeability of gelatin is due to its structure. Under the microscope, it resembles transparent spaghetti. When wet, the gelatin swells considerably. This swelling makes the structure more permeable. The higher the temperature, the more swelling and the easier it is for fluids to enter and leave. In its swollen state, agitation forces fresh developer in and spent developer out. This is primary relationship between temperature and development rate</p>

[Mike Gammill]

<p>Adjustment of development time has been one method of adjusting contrast that still has some merit today even though many photographers scan their negatives and adjust in Photoshop. Take a medium speed film such as Plus-X, for example. Under average lighting conditions many users rate it at box speed (as I do) and obtain negatives that print well (or scan well). Under high contrast lighting (intense sunlight, bright spotlights, etc.) you might rate it at 64 or 80 and redude development to lower contrast. Under flat lighting a rating of 200 or 250 might be used with a slight increase in development. I've found, for example, that rating Plus-X at E.I. 200 on a cloudy day and adding 30 seconds to my time in HC110 dilution B gives a nicely printable negative.<br>

If you have too much or too little contrast and don't scan negatives you can also compensate in printing by using variable contrast paper in printing.</p>

[Alan Marcus]

<p>It is the developing agent that is the active ingredient, reducing the exposed silver crystal to its two component parts. The most popular developer formula is hydroquinone in conjunction with metol. Hydroquinone works slowly and yield higher blackening (density) and higher contrast at the expense of image detail. The developing agent metol is fast acting and yields needed detail. </p>

<p>Fine grain developers contain a fast acting developing agents as they physically cause emerging metallic silver to move (dance). As they move they collide and bump, this reduces clumping. It is clumping that is the culprit when it comes to graininess, as individual silver particles are super tiny (microscopic).</p>

<p>Some fine grain formulas contain paraphenylenediamine, a slow acting developer that yields smaller grain sizes. Slow acting developing agents reduce clumping. Most fine grain formulas contain a silver solvent. Silver is slightly soluble in sodium sulfide. This agent attacks the metallic silver particle and reduces its mass. The combination of paraphenylenediamine and glycin produces as slow acting fine grain formula. Sodium sulfide does double duty; it retards aerial oxidation and neutralizes staining agents that are generated by oxidation. </p>

<p>As development, proceeds, one product is a negatively charged halide ion. This ion forces the solution to an acid condition. Development takes place best in an alkaline environment. Alkali substances are present to counteract, however, the alkali is an accelerator that must be restrained otherwise fog will result. Potassium bromine is the restrainer. This is an apparent paradox, however all work together to balance the pH of the solution. </p>

[paulie_smith1]

<p>the simplest way to see how this changes is to shoot some film. Identical exposures on the roll. Then cut it into thirds and develop one normally, the next one same time at 5 degrees higher temp and the third higher yet. Then make a print from each to see how it looks in the final image.<br>

With some films you will have major differences. With others not so much. The exercise will benefit you with real world experience in your own darkroom with your gear and film.</p>

[profhlynnjones]

<p>That is like saying does oxygen affect breathing!<br>

Time, Temperature, Exposure, and to a slightly lesser extent agitation are critical. To affect the desired density and contrast, the necessary time and temperature are critical. Get a great liquid thermometer (not a dial type) and find an appropriate developer time and temperature, in F scale it should bu +/- 1/2 degree, in Cscale it should be +/- 1/4 degree. In 100/125 ISO films agitation ever 30 seconds is most common after a 15 second continuous agitation initially., in higher speed film many users agitate once a minute. A few users do still development but I'm opposed to that for technical reasons.<br>

Lynn</p>