The MTF is a criterion that describes accurately the optical system performance of imaging systems. It represents the transfer of the contrast modulation from object to image as a function of the spatial frequency (Fig below).

In other words, it describes the system ability to resolve details and is given from measurement numerically (by percentage) on a chart (modulation versus frequency).

In principle, a resolution target that represents the object is placed at the focus of a collimated beam impinging on the optical system that transfers its image to a sensor (Fig below), inputting the identified signals into a computer.

Specially designated software provides a graphical presentation of the MTF results (%), see Fig below. In addition, the observer who sees the image target on the computer screen determines in which group (representing different frequencies) of the resolution target the black and white lines can be seen.

The formal definition of the MTF is

and the definition of the contrast is