Abstract: An optical pyrometer and method of use provides a dual path optical system for processing light from a radiating stationary object or a moving thermal stream. Light is collected by primary optics forming an intermediate image in a plane of a field limiting aperture for establishing a preferred field of view. The light is then split into a pair of complimentary beams with one beam directed through a long wavelength filter and the other directed through a short wavelength filter. Both beams then move through separate secondary optics and are then rejoined and directed as normal non-overlapping and adjacent images onto a digitizing detector for capturing the images. Signals from the detector are handled by a computer where a ratio mapping of pair of signals from corresponding points on the two images is constructed and displayed on a monitor for viewing a temperature map of the object or thermal stream.