(Color online) Schematic representation of the THEMIS post-focal instrument. The converging light coming from THEMIS is collimated by lens l1, which also produces an image of the telescope pupil in the SLM aperture. The linear polarizer’s P azimuth is aligned with the SLM azimuth. There, a diffraction grating produces three diffraction orders with different vortex phases (−1,0,+1), and those are re-imaged by l2 onto the CCD. Therefore, all the diffraction orders share the same optical path, and the phase diversity algorithm is applied to images taken in different parts of the same CCD.