Entrance slit and the grating are fixed and the exit slit scans across the Rowland circle.

A method which is based on Rowland mount and use ZEMAX software to design flat field holographic concave grating is given in this article.

All components of the monochromator were laid on the Rowland circle. The position of the exit slit was changed to obtain the corresponding monochromatic light in the exit slit of the monochromator.