Understanding Neutron Radiography Reading V-Kodak Part 2 of 3

3. Film type. Changes required by the use of a film different from that for
which the exposure chart was prepared can be made by a somewhat similar
procedure. Using the characteristic curve shown in an earlier figure and the
method described in Example 2 in "Overlay Methods“ and "Nomogram
Methods", it can be found that Film Y requires four times more exposure than
does Film X to produce a density of 1.5. The logarithm of 4.0 is 0.60 (See
Figure 53). A mark is put on the margin of the exposure chart a log exposure
interval of 0.60 below the printed arrow. When the transparent overlay is in
this position, exposures for Film Y can be read directly. The Figure 58 shows
this arrangement. If the new film were faster than the one for which the chart
was prepared, the same general procedure would be followed. The relative
exposure required for the new film would be taken so that it was greater than
1, and the logarithm of this number would indicate the log E interval by which
the new mark would be placed above the printed arrow on the chart.
Charlie Chong/ Fion Zhang
Radiography in Modern Industry. Rochester, NY: Eastman Kodak Co. 1980