MTF chart information

MTF (Modulation Transfer Function) is a kind of index used to evaluate lens performance, which represents the extent of subject contrast reproduction as spatial frequency.
The MTF chart here shows the contrast on the vertical axis, and distance from the center of the image on the horizontal axis. For the spatial frequency, 10 lines/mm shows a low frequency, and 30 lines/mm shows a high frequency, resulting in the MTF graph. On the graph, the solid line represents the S direction (sagittal direction and radiation direction) MTF, and the broken line represents the M direction (meridional direction and concentric circular direction) MTF.
In general, a low-frequency MTF is proof of a clear, high-contrast lens, and a high-frequency MTF is proof of a sharp lens with high resolving power.