Bio-Rad EXQuest Spot Cutter - Manual (Page 412)

Appendix D. GS-700
D-13
Finally, enter the values in the appropriate fields under the Diffuse column. After the
step tablet is scanned, the software will associate each density value with its
corresponding segment on the step tablet.
The step tablet density values do not need to be entered each time you calibrate. Once
they have been entered and saved, they will be automatically recalled when the
calibration strip is scanned. You only need to enter new values if you use a new step
tablet.
When you finished filling out the Step Tablet Values form, 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. D-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
⋅
=