An imaging infrared spectrometer system includes an ATR unit (10) having a sample window (12) above an optical system (19) that directs radiation through the window onto the sample and directs radiation from the sample via corrective optics (40) to an imaging detector (4). The corrective optics is in the form of a wedge-shape prism (40) with a reflective surface (28) and is located near a focus of the optical system (19). The wedge prism (40) is effective to correct the focal plane orientation and anamorphic magnification at the sample.