Position measurement of optical elements in a lithographic apparatus

A device manufacturing method, comprising:

• projecting a beam of radiation onto a radiation sensitive substrate via a plurality of optical elements of a projection system;
• measuring the position and/or an orientation of at least one of the optical elements;
• and
• using a part of one or more optical element measurement systems mounted on a metrology frame structure,
• wherein:
• the plurality of optical elements, a patterning device stage, and a substrate stage are arranged so that, in a two dimensional view on the projection system, a rectangle envelops the plurality of optical elements, the patterning device stage, and the substrate stage;
• the rectangle is defined as small as possible;
• the metrology frame structure is positioned within the rectangle;
• the plurality of optical elements comprises an outer group of optical elements surrounding the metrology frame structure;
• and
• most or all of the optical elements comprise grazing incidence mirrors.