A confocal, all-reflecting, infinity corrected microscope was developed to improve infrared microspectrometer (IMS) systems. This system consists of a Fourier transform spectrometer, an infinity corrected all-reflecting microscope, a viewing system for visible light microscopy, a single remote confocal mask for aperturing in either a transmission or reflection mode and an infrared detector. The radiant energy passes through a confocal aperture mask as it travels from the source to the sample and through the same confocal aperture mask as it travels from the sample to the radiant energy detector. A single confocal mask insures that the sample defining mask's size, geometrical shape and orientation are always matched. Mask alignment is assured and simplified since only one adjustment is needed. An aperture beam-splitter is used for reflection measurements. This system simplifies the operation of the microspectrometer, permits the use of standard commercial infinity corrected microscope optical components and reduces the cost of IMS accessory microscopes.