T.O. 33B-1-1
6-54
conditions. An example of its use follows, but note that 3 out of 4 terms in the equation must be known before it can be
used.
Figure 6-24. Nomogram to Assist in Solving Equation U
g
= Ft/d.
6.7.2.5.2
Suppose that a specimen having a maximum thickness of 1.5-inch (t) is to be radiographed at 20-inch source-to-film
distance (d) using a source of effective focal size 6mm. The need is to establish an approximate value for U
g
. The
steps in using the nomogram are:
a. Plot the points A and C that represent the known value of F and t. The pivot line is intersected at B.
b. Plot a line joining point D (the value of d) and B. The extension of this line at E gives the value of U
g
(0.47mm).
6.7.2.5.3
It should be remembered that unsharpness of the radiographic image is also affected by the characteristics of the X-ray
film. Therefore, the total image sharpness may be controlled by either geometrical unsharpness or film unsharpness.
Whichever unsharpness value is the greater will control the total image unsharpness. In a given situation, the
