For the calibration, we use an image from the LaB6 standard collected at a given sample-detector geometry. Knowing a wavelength and a pixel size (172 x 172 μm), the horizontal axis of each frame in pixels can be transformed into 2θ.

The easiest way to do so is by using DIOPTAS software.

Open DIOPTAS. Make sure you are in the calibration mode, which should be selected on the left side of the window:

 

Preparation.

Load the calibration image by clicking the “Load file” button on the upper right side of the window. Now you can insert the starting values for the calibration in the menu on the right. The calibration procedure will estimate distance and center position of the x-ray.  Approximate sample-detector distance, wavelength and pixel width/height has to be defined. Choose the correct calibrant from the Calibrant drop-down list (in most cases it is LaB6).

Peak Picking.

Dioptas needs an initial guess for the position of some of the rings (arcs). For that, you need manually to mark a few (starting from the rightest one). The parameters for peak selection are given in the “Peak Selection” section on the right side of the calibration module when “Calibration Parameters” is selected. By default, it starts with the first ring in an automatic mode with an increase of a ring number after each marking. To mark a ring, mouse click on its middle (zoom in by using the drag-zoom or mouse-wheel zoom). Dioptase will try automatically to find a marked ring (if it is not successful (or a ring is hidden in a 'chip' from the detector), untick "automatic increase" and choose "single peak search", then mark 5 - 10 points on the same ring. Do not forget to increase the peak number after if you want to continue in a manual mode. Return to automatic search and tick "automatic increase"  to return to an automatic mode back). You need to mark and find 6 - 7 rings.  

The Calibration and Refinement.

After the peaks/ring(s) have been selected, we can start the calibration procedure. This is done by clicking the “Calibrate” Button on the lower left of the interface. This will calculate the geometric parameters based on the current peak selection and then automatically refine the calibration parameters.

When the procedure is finished, it will jump to the “Cake” tab (top tab-bar above the image) and show the cake image. Ignore this image. Important resulting calibration parameters are shown in the "Fit2d Parameters" tab. If calibration is correct, "Distance" is reasonably close to an approximated one, and all rings are found (click the "Pattern" tab at the top). "Center X"  and "Center Y" is >5000 px and around 97 px, respectively (change "Center Y" to 97 px if it differs too much, and then update).

The current calibration parameters can be saved by clicking the "Save Calibration" button on the lower right of the user interface. To fast reuse the calibration, load it by clicking "Load Calibration".