I disclose, in an optical pyrometer system, the combination comprising an optical system for receiving and focusing incident radiation from an object, a beam splitter disposed in a light path of said optical system, for passing a portion of said incident radiation to a direct viewing aperture of said optical system and the remainder of said incident radiation to a second aperture of said optical system, light sensitive detecting means juxtaposed to said second aperture for receiving incident radiation passing therethrough, and said direct viewing aperture and said second aperture being sized so that the light sensitive area of said detecting means is completely covered by said second aperture radiation when an object image focused by said optical system completely fills said direct viewing aperture.