IRIS H-band images of HD 66598 A (two right panels) and HD 66598 B (two left panels). The IRIS quadrant, VLTI input channel number, telescope, delay line, and fringe sensor are indicated at the top of each panel. The magnitude difference between the stars is Δm_H ~ 1.8 and the exposure time was 0.2 s for all IRIS quadrants. The red cross in each panel indicates the guiding pixel, i.e. the target for the image stabilisation control loop, defined as the position of optimal alignment with the FSU. Because of fast atmospheric turbulence, the IP4 beam was not well aligned at the time of exposure.