A computational investigation in the present work has been used to design optical system (Four Elements Objective Lens) to show the suitability of some infrared materials (Si, Ge, AMTIR1, KRS-5, and ZnSe) for the elements of optical designs with aid of ZEMAX package. Optimization process using merit function has been conducted to determine the must favorable optical properties (diffraction, aberration, size of spot, and size and shape of the system). Such designs have been operated in the middle infrared region of spectrum 3.2-4.2 ?m. The computations obtained by the ZEMAX package shows the performance of those infrared materials through the parameters, focal length, back focal length, f-number, numerical aperture, field of view, Seidel sum for spherical aberration, intensity distribution and fraction encircled energy of the systems and images projected in the detection area. The results have been compared with those obtained with aid of Visual Basic program where a high degree of agreement has been found. The specifications of the optical systems that have been put forward in present investigation can be practically realized.