The ACOFAM combines an optical method of frequency analysis with electronic data unit and display to obtain a fast and accurate measurement of the Modulation Transfer Function of lenses and complete systems in the visible range. Some extra devices are described in order to convert the standard ACOFAM to the infra-red spectral range (5–20 μm). Results of measurements on a 50 mmF/1 developed by the Optical Division of Engins MATRA are shown.