To focus the lens correctly, just use the camera as intended and without diffraction optics and adjust the lens so a sharp picture can be seen. Now insert the diffraction optics, so the red part of the spectrum is on the right side of a picture. Get a red (650 nm) and UV-laser (405 nm) pointer and calibrate the software.
* I think i damaged my camera. Random noises appear on ccd (readouts?) sometimes.