Jose,  Geometric modulation transfer function (MTF) for a given frequency v is calculated as follows.  The spot diagram after ray trace is summed up in one direction (x) by counting the number of spots in each increment dx.   The number of spots is plotted against x to get the line spread function A(x).   A(x) cos(2 pi vx) and A(x) sin(2 pi vx) are integrated and then normalized by the area under A(x) to give Ac(x) and As(x).   A(v), which is the square root of Ac(v)^2+As(v)^2, is MTF(v).   Please see W.J.Smith's "Modern optical engineering.      Regards,  Shigeo

Oh, I knew that algorithm. However, I know that mayor optical software, such as XEMAX and OSLO uses FT of the spot diagram. I also knew recently that CODE V do it similarly.

Further confirmation from any CODE V user will be welcome.

José Antonio