Viewing and measuring apparatus

Claim 1

A viewing and measuring apparatus for a substantially planar object comprising: (a) a viewing system having an optical viewing axis which intersects the object at a viewing point; (b) a grating interferometric measuring system having an optical measuring axis which intersects the object at a measuring point; (c) optical modulating means superposed with the object, said modulating means providing relatively high spacial frequency content matching that of the measuring system; (d) reflective means superposed with said object for providing at least partial reflection of incident spectra; (e) means for supporting the viewing system and the measuring system relative to one another such that the viewing system axis and measuring system axis intersect the object substantially coaxially and whereby the viewing point and measuring point are substantially coincident; (f) means providing that a spacial frequency plane of the viewing system is substantially optically coplanar with a spacial frequency plane of the measuring system to define a common spacial frequency plane, at which plane relatively high frequency spectra operatively associated with measurement are spacially separated outwardly from relatively low frequency spectra operatively associated with viewing; (g) reflecting means optically associated with the spacial frequency plane for selectively deflecting the high and the low frequency spectra from each other to effect axial separation thereof and whereby the separated low frequency spectra can be utilized in said viewing system; (h) said measuring system including photo detection means fixed relative to the viewing-measuring axis for receiving separated high frequency spectra reflected from the object; and (i) means for translating the object relative to the viewing-measuring axis within the plane of the object to effect visual translation of the object in the viewing system while interferometrically measuring the translation.