MOS observation of spiral galaxy NGC 4303

The very efficient multi-object-slit observing technique with the multi-mode instrument FORS1 is demonstrated on the Virgo cluster galaxy NGC 4303. Nineteen moveable slits at the instrument focal plane are positioned so that the faint light from several H II regions in this galaxy can pass into the spectrograph, while the much stronger "background" light (from the nearby areas in the galaxy and, to a large extent, from the Earth''s upper atmosphere) is blocked by the mask.