As will be shown, the phase of this funcion indicates the azimuth of the c-axis, and the amplitude can be used to determine the inclination. Routinely, the circular polarization image is captured first, the rotation images next, and the tilt images last. This will yield the correct exposure.
Correct exposure is tested by acquiring the image and inspoecting the histogram.
Adobe Photoshop is preferred over NIH Image because it allows batch image acquisition whereas NIH Image permits single image acquisition only. The initial position is when the thin section is aligned parallel to the vertical and horizontal image axis of the camera.