So which is it? The short answer is (predictably): It depends. Two factors are operating here. Increasing film exposure slides all scene elements to positions of higher density on the film curve, and increased density means increased grain. Were this the only factor at work, overexposure always would result in more graininess. But grain also varies with film contrast: More contrast (longer development time) means more grain, and vice- versa. So if overexposure requires pull processing (a shorter development time), this acts to counter the grain-enhancing effect of simply overexposing. This brings us back to the last issue’s column.
There we discussed the fundamentally different curve shapes associated with a pair of films, comparing the same scene exposed normally and overexposed two stops. That issue’s overexposed pair of curves is presented again here as Figure 1 to illustrate their relative shapes. We noted the pink-curve film should be developed for the same time whether exposed normally or overexposed, whereas the blue-curve film required a pull process to ensure all four negatives would print on a common paper grade. The tonal consequences were significant. The two films produced similar tonal characteristics when exposed normally, but with overexposure, the (pulled) blue curve yielded less shadow detail, darker midtones, and enhanced separation of highlight tones (see the July/August 2007 PT for a more detailed explanation).
Now consider the density swatches of Figure 2. These are scans of prints from uniformly exposed middle-gray patches from the two films, both exposed normally and overexposed. They are printed to a common density, as would be the case in preparing actual prints of full scenes, and enlarged sufficiently to visualize the differences in graininess.
As an aside, the normally exposed pink-curve film is slightly grainier than the blue one, but this is simply an inherent characteristic of the two films. Focus on the right pair, where both received additional exposure. The pink film required no change in development time. Contrast is the same with normal and overexposure; only the first factor is operating: More exposure, higher densities, more grain (substantially more!). But the contrast-reducing pull process needed for the blue film almost exactly counterbalanced the effect of overexposing: Overexposing increases graininess, but the drop in contrast almost exactly wiped that effect out—graininess remains virtually unchanged with overexposure.
Summing up these two columns, the choice of characteristic curve shape is a guaranteed predictor of these key image properties: A pink-type curve shape with rolling shoulder produces, with overexposure, enhanced shadow detail, brighter midtones, compressed highlights, and markedly increased graininess. A blue-type curve with a lower scale sag yields more compressed shadows, darker midtones, and enhanced highlight detail, all with no grain penalty.
Which is the better path? Not for us to say—it depends on the image and the photographer’s intent. But we offer our blessings to the contact-printing, large-format shooter, who can legitimately ignore this column and any other grain-related issues.