The use of photographic emulsions to record the spatial distributions and the intensity of radiation in spectroscopy, x‐ray diffraction, astronomy, and other fields is hampered by the sensitivity of the characteristic curve to development and exposure conditions. The deflection of a microphotometer or microdensitometer of conventional design cannot be made directly proportional to the intensity of radiation which is incident upon the element of area of the film or plate at the time of exposure.The recording microdensitometer described herein incorporates a device, termed a function transformer, which automatically and continuously converts densitometer deflection values to exposure values, and two pen and ink recorders. One recorder produces a direct exposure trace, while the other records the usual densitometer trace. An integrator permits the integrated exposure to be evaluated for any desired portion of the plate or film.The apparatus described can be used with any film or plate to which a suitable calibrating exposure has been applied and over the area of which the characteristic curve is sufficiently uniform.