Photonics Dictionary


An instrument used to measure the luminance (brightness) of a distant object. The object is viewed through a small telescope, and a mirror in the focal plane reflects an internal illuminated surface to the eye alongside the image of the object being measured. The luminance of the internal surface can be varied manually until it matches the luminance of the distant object, and then can be read off a scale. Some small telephotometers are used by photographers to measure the brightness of a scene; these are called spot photometers.
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