The present work aims to design an optical system for infrared (IR) homing head. The homing head of interest works through ( ) m µ 5 3 − atmospheric window, so it must have high quality characteristics. The characteristics of the optical system design include the point spread function (PSF), modulation transfer function (MTF), total spot size (ZT)or focusing, and range (R). These characteristics are determined with the aid of special mathematical methods, which give the efficiency and accuracy of the adopted optical system design. The work has been performed in multi-stages; the most interest of them are namely design improvement and programming for determining the efficiency of the suggested optical system design. The improvement stage depends originally on a standard optical system design for IR homing head. Some modifications and improvements have been imposed on this standard design to achieve a new one of high quality characteristics. These improvements include choosing the most suitable material for the firist element in the system, and optimum features for each optical element in the suggested design. An improvements stage was then followed on the radius of curvature, thickness, and diameter of the optical elements constituting the system. The improvements process was carried out by Zemax software. The improvements stage included the implementation of specially developed software for determining the characteristics of the IR homing head since the most important; the range could not be determined directly by the Zemax software. Therefore, a multi-task software was designed by using the Visual Basic programming language. The new software is called OID which is short for optical infrared design; it works through Windows operating system. This software is able to plot any optical design graphically, and can determine the main parameters that influence the efficiency of the optical system such as PSF, MTF, ZT, and R. These parameters have been computed by special methods based on some mathematical relations. The present work has gained some credibility when a comparison between the results of Zemax software and those of the designed OID software have been carried out, which have shown harmonic behavior, which insure succeful results. It has been found that with the aid of the proposed optical system a target at a range of about 7.50 km can be detected under clear weather conditions using an IR radiation of m µ 4 wavelength. Furthermore, the total spot size as small as m . µ 6 10 can be projected on the detector with the lowest possible aberrations. The newly develop OID software can be employed in future on other optical system designs such as those used in the field of wireless laser communication systems.