A monolithic spectrometer (10) for spectrally resolving light (L), comprises a body (2) of solid material having optical surfaces (3,4,5,6a-6c,8) configured to guide the light (L) along an optical path (E1,E2,E3,E4) inside the body (2). The optical surfaces of the body (2) comprise a segmented focusing surface (6a,6b) comprising first and second continuously functional optical shapes (Ca,Cb) to focus received parts of respective beams (La,Lb) onto respective focal position (fa,fb) in an imaging plane (P) outside the body (2). The second continuously functional optical shape (Cb) is separated from the first continuously functional optical shape (Ca) by an optical discontinuity (Dab) there between.