Calibration of Microdensitometers
Richard E. Swing · SPIE eBooks · 1997
The problem of calibration of densitometers was discussed at some length in Chap. 1. Discussion of the necessity for calibration holds even more so in microdensitometry. Classical microdensitometers, because their illumination and collection geometries vary with configuration, present a more complicated set of problems. With the scattering of each specimen perhaps also varying because of a change in materials, processing, or both, the verisimilitude of the scanning output is sometimes questionable. In the interlaboratory exchange of information, it is critical to reduce optical densities to a standard density upon which all can agree. This caveat similarly applies for other instruments within the same laboratory, even of the same make and model. This way, identical results from the same specimen can be obtained with different instrumentation. The reduction to standard density is the key, and this is achieved through calibration. Commonly, the standard density is diffuse (visual) density or DVD, because the properly equipped laboratory will have a densitometer calibrated to that standard from which properly calibrated artifacts can be created for calibrating the microdensitometer. The need for, together with the general approach to, microdensitometer calibration was presented in 1956 by Altman and Stultz. Subsequently the ideas expressed in that paper were expanded and detailed by McCamy and Derr. Recently, a comprehensive paper on the subject was published by Fitzgerald and Swing, and that paper serves as the basis for this chapter.