Optical system with an aperture stop

An optical system, comprising:

• an aperture stop comprising a solid portion and an aperture with, the aperture having an edge configured to delimit an outer circumference of a beam path of used radiation in the optical system;
• and
• a heat stop upstream of the aperture stop along the beam path of the used radiation in the optical system,
• wherein:
• the heat stop comprises a solid portion and an aperture;
• the aperture of the heat stop has an edge;
• the solid portion of the heat stop is configured to partially shade the solid portion of the aperture stop from extraneous radiation in the optical system, the extraneous radiation propagating outside of the beam path of the used radiation in the optical system;
• the edge of the aperture stop is excluded from the shading of the extraneous radiation in the optical system;
• there is a space between the edge of the aperture of the heat stop and the outer circumference of the beam path of the used radiation in the optical system so that the used radiation does not impinge on the solid portion of the heat stop;
• and
• the edge of the aperture of the heat stop is at most two millimeters from the outer circumference of the beam path of the used radiation in the optical system.