Abstract: A microscope for use in transmissive and reflective infrared spectral analysis of a sample positioned on a sample plane. The microscope uses a collimated beam for infinity correction. A collimated irradiating beam of infrared energy is input to the microscope and focused through a single confocal aperture whereupon the beam is re-collimated and provided to a focusing lens. The focusing lens focuses the beam on a subject sample which generates a resulting image beam. The resulting image beam is re-collimated and provided to an optical element which focuses the resulting image beam back through the single confocal aperture and to an infrared detector. In a preferred embodiment, the size of the single confocal aperture is adjustable and a dichroic element is included for providing simultaneous viewing and infrared measurement of a measured sample. Also in a preferred embodiment, a detector mounting apparatus is included for facilitating orientation of a detector at an infrared output of the microscope.