The Modulation Transfer Function (MTF) is the ability of an optical system to transfer contrast at a particular resolution from the object to the image. It is a curve as a function of spatial frequency which describes how well things relative to each other depending on their size can be distinguished by the camera. MTF is affected by: camera design, environment ( illumination ), and focus.
MTF is calculated from SFR and LSF.
The Spatial Frequency Response (SFR) is measured using a half-Moon target which is tilted a few degrees. This target gives differences between blackbody and background in a single image.
SFR measurement readings is a step-function whose derivative is Line Spread Function (LSF).
LSF is a function of the angle of view which describes the sharpness of the camera.
MTF comes as a result of the Fourier Transform of the LSF.