Areas sensitized above Zone 1 continue to grow in density as development continues. Once areas sensitized to Zone 2 reach that density, they gain slightly greater density with continued development—but they won’t even reach Zone 2½ without excessively long development times. Once areas sensitized to Zone 3 gain that density, they can be developed nearly up to Zone 4 with increased development times. Areas sensitized to Zone 4 can be pushed beyond Zone 5 in density with extended development times.
The amount of development time needed for each zone to reach its proper density is known as the “normal development” time. How do you determine “normal development time”? By finding out how long it takes to develop any exposed zone to that exact density. For example, normal development time is the time required to develop an area placed at Zone 5 (the gray meter reading) to Zone 5 density. At the start of development, the exposed (i.e., sensitized) Zone 5 area has no density, but as development proceeds, density increases. It quickly exceeds Zone 1, and then surpasses Zones 2, 3, and 4 before finally achieving Zone 5 density. That’s “normal development time” (for that combination of film and developer). If development continues beyond that point, the density will exceed Zone 6 and ultimately reach Zone 7.
But how do you identify true Zone 5 density? Let’s go back to the beginning of Chapter 8 where we defined standard exposure. Once you find the standard exposure, place the Zone 5 negative in the enlarger (at the same height and aperture you used to determine the standard exposure) and give it that same exposure. If it’s true Zone 5 density, the print you get will be exactly the same tone as the 18 percent gray card. When you develop the Zone 5 negative for the appropriate amount of time to achieve that density, you have found the normal development time″. (This fills in the temporary gap in the explanation of the zone system at the beginning of Chapter 8. It may be worthwhile to reread those pages now.)
Each higher zone grows progressively denser with increased development time. The portion of the negative exposed at Zone 6 (one stop brighter than the gray meter reading) achieves Zone 6 density in the normal development time, but it can exceed Zone 8 density with greatly extended development time. Increasing the development time beyond normal not only shifts the density of each zone equally, but also expands each zone in proportion to its original placement.
If development is terminated before the normal development time, precisely the opposite effect occurs. In that case, the density of each zone decreases in proportion to the original exposure on the zone scale. The higher zones are reduced in density more than the lower zones. Zone 1 is fixed in density no matter what development the negative is given. Those areas exposed as Zone 2 will not quite reach full Zone 2 density in less than normal development time. Zone 3, however, will begin to show significant changes, perhaps dropping to Zone 2
As you progress up the tonal scale to higher exposed densities, each is developed to a higher density than its predecessor, but each is reduced below normal density by a greater amount than its predecessor. Zone 9 may drop to Zone 7, while Zone 11 may barely exceed Zone 8 with a shortened development time.
Note
Increasing the development time beyond normal does not simply shift the density of each zone equally, but expands each in proportion to its original placement.
The Bellows Analogy
A simple way to grasp the concept of progressively increased densities with extended development times, and progressively reduced densities with shortened development times, is to think of each successive zone as a number on the successive pleats of a camera bellows. When development begins, the bellows are crunched down completely and each zone placement has zero density. As development progresses, the bellows are slowly extended to the right from the fixed point on the left so that the pleats, or zones, separate from one another—meaning that they separate in density. The longer the development time, the further the bellows are extended to the right, and the greater the density of the higher zones up to maximum negative density (Figure 9-2).
Negative density and print tonal scale Please note that Figure 9-2 is not a model of actual negative densities during development, but rather a schematic of what happens to densities as development proceeds. I will refer to it in the following examples to be consistent within the text, but don’t expect your combination of negative and developer to yield the same results as those shown here. Yours should be close, but not exact. (See Time/Temperature Development Charts for several films in Figure 9-6–Table 9-4.)
Figure 9-2. Density Increase During Development Time—The Barnbaum Bellows Analogy
Within the first minute of development, the zones begin to separate. At four minutes, Zone 1 is fully developed and Zone 2 is near its normal density, while the higher zones are noticeably falling short. If you choose 6½ minutes as the normal development time (my development time for Ilford HP5+ or Kodak Tri-X film in Kodak HC110 developer), you will see that the zone placements—the sensitization levels of the latent image, which are the numbers on the pleats—correspond to the developed densities. Beyond 6½ minutes, all zones except 0 and 1 continue to grow ever denser.
For example, note in the schematic representation at three minutes development time, the exposed Zone 4 reaches just above Zone 3 (a loss of nearly a full zone from its normal development density) whereas Zone 10 reaches only a bit above Zone 6, which is a loss of nearly 4 zones from normal. This shows that the higher zones lose more density than the lower zones with reduced development times. Contrast is decreased when development times are reduced below normal.
Conversely, with 12 minutes of development the exposed Zone 4 reaches 4
Another way of representing the development characteristics of the negative is via a graph (Figure 9-3), where the X-axis (the horizontal axis) represents development time in minutes and the Y-axis (the vertical axis) represents density. Each curved line represents the increase in density of an exposed zone as development proceeds. All exposed zones start the development process with no density, and density increases in proportion to the initial sensitization. At my normal development time of 6½ minutes, each exposed zone reaches its proper density. Beyond 6½ minutes, density continues to slowly increase (except for Zone 1) in proportion to the initial sensitization.
For those who have trouble understanding graphs, a brief explanation may help. Choose any one of the curved lines, such as the dark line which represents Zone 5. It begins at the lower left, like all the other lines, because it has no density at the start of development (0 minutes). As you move to the right, which represents elapsed development time, the curve rises, representing increased density. When you stop at any point along the curve, the distance from the Y-axis (the left edge) represents elapsed development time, while the height above the X-axis (the bottom) represents density. In three minutes, for example, negative density barely surpasses Zone 3. In 6½ minutes (shown as normal development time in this graph), it exactly reaches Zone 5 density. In 12 minutes, it exceeds Zone 6 density. Follow any other line to see how development proceeds with time.