What makes the fractional gradient speed method significant and still relevant is its connection to the print judgment speed test. Photography is a subjective medium and the only way to determine what process works or not is to evaluated the result from the process. The first excellent print test was just such a psychophysical test. Photographs were made of a range of subjects over a period of time. Detailed information for each scene and exposure was recorded. Sensitometric tests were run at each step. All of this is thoroughly covered in the Loyd Jones paper The Evaluation of Negative Film Speeds in Terms of Print Quality.
A series of prints were made from each negative and these prints were judged by a panel to determine the quality of the prints. The negatives were then evaluated to determine the correlation. The conclusion was print quality increased as negative exposure progressively increase, but only to a point. Then the level of quality leveled off.
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The initial point where the prints were deemed excellent is call the first excellent print point. The results from the test indicates there is no ideal or correct exposure with black and white negatives. Only that a negative shouldn’t be exposed below a certain point. In practice, there are advantages to using the minimum necessary exposure. Exposure times are increased. Sharpness is maximized and grain is reduced. When the tests were conducted in the late 30s, the average negative size would be considered large format today and didn’t require a high degree of enlargement. Consequently, the range of “over exposure” without a change in print quality would be larger than with 35mm film. This still leaves a bit of room to chose from. What is key about determining the first excellent print point is that it defines the minimum, the base to work from.
As Nelson and Simonds writes, “it is too time consuming to use the print judgment method except for basic studies. A sensitometric method is much more rapid.” Once the basic study was finished, it was necessary to find a sensitometric alternative that would yield consistent results with was many different types of film agreeing closely to the print judgment speed tests. The legitimacy of any method is contingent upon this point.