Select a guide field: To focus the guiding camera shift a reasonably bright star into the guiding camera field of view (GFOV). Press buttons + or - of the guiding field control unit to move the GFOV. The GFOV is displayed as the small square in the Sky Graphics Window (Fig. 14 and 15).
Set guiding camera into ``focusing mode'': Press misc and select focusing with the left mouse button. Proceed as in the Section 3.1 before to obtain Gauss-Fits to the brightness distribution of your star.
Set a starting focus value: The focus is set in the guiding camera focus control unit of the guiding camera section (Fig. 14). The focus is changed by pressing the buttons + or -. A good starting value for the guiding camera focus is 19.0. The values are in arbitrary units.
Make a guide focus imaging sequence: Change the focus stepwise, while the guide camera is in ``focusing mode'' and record the FWHMs displayed. The best focus is the one where the FWHMs are minimized. Again, you may choose step sizes of four. A reasonable FWHM for a well focused guiding camera should be similar to the FWHM obtained for the main camera.