The Modulation Transfer Function is a measure of spatial resolving power. It can refer to a medium, such as film, or a lens, or any part of the scene-to-screen chain. It is akin to frequency response in electronic images. To assess the MTF of film, it is exposed to special test images comprising sine-wave bars of successively higher frequencies. The results on the processed film are assessed by measuring its density over microscopically small areas to obtain peak-to-trough values for the different frequencies. These results should then be corrected to allow for the response of the lens, the test film itself and any D/Log E non-linearities.
In a practical film system, the film images pass through many components including the camera lens, intermediate stocks and contact printing to the projection lens. Each of these has its own MTF and the system MTF can be calculated as follows.
MTFsystem = MTF1 x MTF2 x MTF3 etc
See also: Resolving power