It has been prototyped the basic optics and electronics of a crossed Czerny-Turner spectrograph to work at different wavelengths. The optical system of the spectrograph prototype has been simulated using OSLO software in order to optimize the capture of the light spectrum. The study that is presented in this paper is based on the optimization of the focusing optics orientation that would obtain the smallest y-spot width onto a linear CCD, for different central wavelengths. It has been changed the orientation of the focusing optics trough the simulation, and changes in the spot diagram has been observed and plotted. Finally, we have obtained recommendations using these results, how to adjust the focusing optics in real spectrographs for different central wavelengths. Simulated spectrograph had about 0.25 nm mean resolution with a focusing optics of 100 mm focal length. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).