Cinematography-Theory-And-Practice

Figure 10.19. Changing exposureshifts the image up and down thecurve; too much exposure pushesit off the shoulder, and too littlecrushes it into the toe.Not enough exposureCorrect exposureToo much exposureDetermining the precise film speed, coupled with precise exposure,is critical when the range of light in the scene is greater than thescale of the film. In Figure 10.19, we see three exposures of the samescene, represented by the bars at the bottom of the diagram. Notenough exposure places much of the information completely off thelow end of the curve, while too much exposure places it off the highend. In either case, once you are off the curve, further changes inexposure register no change in the negative; the film doesn’t “see”them. The ideal exposure places all of the information where itmakes some change on the negative; in effect we don’t want any partof the negative to be wasted.If there is too much exposure, two things happen. First, even thedarkest parts of the scene are in the middle range of the curve: eventhe darkest shadows will reproduce as middle gray tones. Graphically,overexposure appears as a shift of the subject brightness range(log E) to the right. (In effect we are making the scene values brighterby opening up the aperture.) Here we see that this overexposureplaces the scene values too much in the shoulder. Some informationis lost in the flat part of the shoulder: lost because the differences ofscene brightness value result in no change in the final density of thenegative.Further, because everything is shifted to the right, none of thescene values fall in the toe of the curve: there will be no deep blackvalues at all in the final print, even though they existed in the origi-the left. Here every subtle nuance of the high tones will be recordedbecause they fall in the straight line portion of the curve. But at thedark end of the scale — trouble. The dark values of the scene aremushed together in the toe. There is little differentiation of themedium gray values, the dark gray values, and the black shadows:in the final print they will all be a black hole. There will be no detailin the shadows — whether or not we can see detail is how we judgeshadows and highlights; it is a phrase you will hear often in discussionsof exposure — separation and detail in the shadows or highlights.If there is no separation of tones and no visible detail in the shadows,they are underexposed. The same applies to the highlights: lack ofseparation and detail means they are overexposed. Exactly what constitutesa lack of separation and detail can be a bit subjective, sincesome areas of a scene might be properly represented as pure blackor pure white. Choosing which areas you expect to have details andseparation can be a little bit of a judgment call.cinematography196