A very-high aperture, purely refractive projection objective is designed as a two-belly system with an object-side belly, an image-side belly and a waist (7) situated therebetween. The system diaphragm (5) is seated in the image-side belly at a spacing in front of the image plane. Arranged between the waist and the system diaphragm in the region of divergent radiation is a negative group (LG5) which has an effective curvature with a concave side pointing towards the image plane. The system is distinguished by a high numerical aperture, low chromatic aberrations and compact, material-saving design.