Submitted by Al …
(Adapted from The Encyclopedia of Photography ©1963)
Compensating developers are formulas which make it possible to record an extended range of subject brightness’son a negative without flattening out the gradation of the entire image, as would result from a simple reduction of gamma. Such developers work by compression of part of the negative scale, while permitting the remainder to be recorded at full contrast.
There are several types of compensating developers and at least one of these, the metol-sulfite developer, has an action which is not difficult to explain.
The best known of these formulas (Windisch) contains only metol and sodium sulfite. (Elon, Pictol, Rhodol, or similar developing agents can be used instead of metol.) See Table 1 below.
Note that this formula contains no alkali of any conventional kind. However, since sodium sulfite is slightly alkaline, it is able to activate the metol to some extent, the result being a rather slow working developer taking 25 to 30 minutes to produce a negative of normal contrast for enlarging.
The compensating action of this developer is due to the omission of potassium bromide, as well as to its low alkalinity. Metol is highly sensitive to the action of bromides at this low pH, and only a very small amount of bromide would serve to very nearly stop its action. In the development of a negative, of course, soluble bromide is released as the silver bromide is reduced to metallic silver in the exposed areas – the more silver produced, the more bromide released into the developer. A good deal of this bromide however, remains trapped in the gelatin emulsion, causing development to stop or be greatly slowed at these points.
The result here is that development continues to a certain degree in heavily exposed areas, after which the released bromide slows down the action of the developer and prevents the build up of excessive density. In shadows and lower middle tone areas, less silver is produced, and less bromide released. Development continues at its full rate, finally producing a negative having normal contrast in shadows and lower middle tones, diminishing in contrast in the higher middle tones and highlights, but having satisfactory separation of tones.
A similar developer is the Kodak D-23 which however, has more sodium sulfite and requires less time for development to normal contrast. It has rather less compensating action than the Windisch formula. See Table 2 below.
As can be seen, the Kodak D-23 has three times as much Elon (metol) and four times as much sulfite as the Windisch formula. The resulting higher alkalinity increases its working speed, but at the expense of some sensitivity to bromide. Hence, the compensating action is less.
The Windisch formula is not particularly fine grained in spite of its low activity. The Kodak D-23 produces slightly finer grained negatives due to its high sulfite content. For this reason, neither of these formulas was very popular when first announced.
Today however, it is realized that fine grain and high acutance do not necessarily go together, and that graininess is essentially a characteristic of the film emulsion. Modern fine grain films, such as Adox KB14, Agfa Isopan IFF, and Kodak Panatomic-X, produce their high image sharpness by means of a thin coating of a very fine grained emulsion.
The major difficulty in the use of these thin emulsion films is the danger of blocking highlight detail with even slight overexposure. To prevent this effect, the use of a developer like the Windisch formula or the Kodak D-23 is recommended.
OTHER COMPENSATING FORMULAS
There is another developer, Pyrocatechin Compensating Developer, also the work of Windisch, which produces very strong compensating action. However, the mechanism of its action is much less clear than that of metol-sulfite developers. It seems to produce it compensation by acting mainly as a surface developer. The gelatin of the emulsion is tanned or hardened by the by-products of development, which appears to prevent further penetration and excessive density. It is possible that some of its action is also due to the formation of a dye or stain image along with the silver image, this producing good printing density in the shadows without the necessity of long development.
Unfortunately, the action of this developer tends to be slightly erratic, its effect depending on the particular film emulsion in use. It is not recommended for general use unless tested thoroughly. The formula is shown in Table 3.
For use take 20cc of Solution A, 50 cc of Solution B, and 500 cc of water. Develop for 12 to 15 minutes in a tank with intermittent agitation. Use the developer only once and discard.
The negatives produced with this developer have a marked stain image and print much more strongly than would be suggested by their visual appearance. Reticulation of the back coating of the film sometimes occurs but has no apparent effect on the image. However, the negative should be handled very carefully while wet. There is some loss in film speed with this developer. Negatives may require about 50% more exposure for full shadow detail. The compensating action of the developer will take care of highlights.
COMMERCIAL COMPENSATING DEVELOPERS
There are a number of compensating developers available in ready mixed forms. Three of these that take maximum advantage of the fine grain, thin emulsion films and produce outstanding results, are Ethol T.E.C., FR X-22, and Tetenal Neofin Blue. All three are one shot liquid concentrates, and full instructions for their dilution and use are supplied by the manufacturer.
Comments