an all - reflective optical system for a projection photolithography camera has a source of euv radiation , a wafer and a mask to be imaged on the wafer . the optical system includes a first convex mirror , a second mirror , a third convex mirror , a fourth concave mirror , a fifth convex mirror and a sixth concave mirror . the system is configured such that five of the six mirrors receive a chief ray at an incidence angle of less than substantially 9 °, and each of the six mirrors receives a chief ray at an incidence angle of less than substantially 14 °. four of the six reflecting surfaces have an aspheric departure of less than substantially 12 μm . five of the six reflecting surfaces have an aspheric departure of less than substantially 12 μm . each of the six reflecting surfaces has an aspheric departure of less than substantially 16 μm .