Abstract: A sensor assembly for measuring temperature at a target location includes a sensor adapted to detect infrared radiation and produce an electrical output. A focusing lens focuses infrared radiation from the target location onto the sensor while substantially preventing infrared radiation from points outside the target location from being detected by the sensor. In a first embodiment, a sensor assembly for a focusing thermometer includes a sensor and a focusing lens. In a second embodiment, a focusing thermometer for measuring temperature at a target location includes a sensor assembly and electronic circuitry that receives electrical output from the sensor assembly and processes the output into a temperature reading. The sensor assembly includes a focusing lens for focusing infrared radiation from the target location onto the sensor while substantially preventing infrared radiation from points outside the target location from being detected by the sensor.