Null Ronchi Gratings as a function of period

In this work is presented in a simple manner, a method to generate null Ronchi gratings. This method consider the period of the Ronchi grating as a function of the x and y positions over the grating, compared to the currently known methods which utilize ray tracing or spot diagrams for the null Ronchi gratings calculus. We compare null Ronchi gratings reported in the literature against gratings calculated with our method. We have found that our method can calculate the Ronchi gratings for any conical surface in a satisfactory way.