Abstract: Observation window, especially for checking the temperature of objects using infrared thermography, including a parallel-faced transparent insert made of a single crystal suitable for radiation to pass through without being substantially modified and/or attenuated, which radiation, whose wavelength may range from the visible to the relatively far infrared emanates from an object whose temperature is to be monitored, housed in a screened cabinet provided with a door or panel against which the window is arranged, wherein the insert is fitted into a support which surrounds it at its periphery and is immobilized with respect to the support, this support being applied in a sealed manner against an aperture made in the door and then locked in position by means which are only accessible from inside the cabinet, the support comprising an external protective cover capable of pivoting about a pin connecting it to this support, so as to reveal the insert and allow observation through it of the object to be monitored by