Bio-Rad EXQuest Spot Cutter - Manual (Page 443)

PDQuest User Guide
F-12
Reflective Step Tablet
For the reflective step tablet, it is recommended that you use the default target values
in the software. Although you can edit these values based on your own measurements
and testing, the default values have been preset based on careful testing and review.
To view or edit the default reflective values, make sure that the Reflective checkbox
is selected in the main acquisition window, then click on the Options button. In the
Densitometer Options dialog, click on the Edit Step Tablet button. The Step Tablet
Values for GS-800 Reflective dialog box will open.
When you are finished viewing/editing the reflective step tablet values, click on OK.
Diffuse Versus Specular O.D.
In the step tablet form, you enter O.D. as diffuse density, and then the software
automatically calculates the specular density.
Specular density is a measure of the light that passes directly through a medium.
Diffuse density includes light that is scattered as it passes through the medium. Step
tablet values are given in diffuse density, but are measured by the scanner in specular
density, and therefore must be converted according to the specular/diffuse O.D. ratio.
This conversion does not affect quantitation.
Fig. F-11. Specular and diffuse density
Diffuse density values are converted to specular optical density units according to the
following formula:
Specular Light (passes directly through medium)
Diffuse Light (is scattered by medium)
Medium (gel, film, etc.)
Specular OD 1.4 Diffuse OD
⋅
=