Tecnai on-line help manual -- Options - UT Southwestern

<strong>Tecnai</strong> on-line help Options 125Options Software version 29.1.11 Measurement with diffraction shiftThe diffraction shift of the <strong>Tecnai</strong> is largely free of hysteresis and can be used to calibrate diffractionspacings, from which camera lengths can be determined. The ring analysis method is usable only atcamera lengths where the rings in the diffraction pattern are well-separated from the center and are nottoo large for the CCD. The indirect diffraction-shift measurement must therefore be used where the ringsanalysis cannot be done, that is for the lower and higher camera lengths.Before the diffraction shift can be used to calibrate camera lengths, it must first be calibrated itself. Thisis done at a suitable camera length, immediately after the camera length there has been calibrated withthe rings. (The software thus does not rely on any existing - potentially inaccurate or even wrong -diffraction shift calibrations in the system.)The procedure followed during diffraction shift calibration is as follows:• Apply a negative shift from the current diffraction-pattern position and acquire image 1, with anegative backlash correction (first more negative, then to the desired position).• Apply a similar but now positive shift from the original position and acquire image 2.• Apply a positive shift from the original diffraction-pattern position and acquire image 3 (position thesame as image 2), with a positive backlash correction (first more positive , then to the desiredposition).• Apply a similar but now negative shift from the original position and acquire image 4 (positions thesame as image 1).• Determine the shift between images 1 and 2, and between 3 and 4. These shifts give the two vectorsused for the calibration.Since drift is not an issue in diffraction, no drift correction is done in the diffraction-shift based calibration.9.2 Magnification Calibration Report Control PanelThe Report tab of the Magnification Calibration Control Panelcontains the controls used for report generation. All reports are inAcrobat Reader (pdf) file format.Two types of report can be created:• A tabular overview of the results of a calibration sessions, displaying the TEM magnification, themeasured value(s) according to the method used, which value is used for the magnification table, theassociated consistency error, and the magnification factor from plate camera to CCD or the ratiobetween nominal and measured STEM magnifications..• A graphical overview of the results of (at most) the last twelve calibrations done.