Abstract :
In this paper a simulation for a mathematical two dimensional model was conducted to assess the presence of defocusing due to telescope aperture quality. The point spread function (psf), Modulation transfer function (MTF), and Fourier frequencies of binary star are computed in the absence and presence of defocusing. The results show that the total frequency components of MTF decreases very sharply as defocusing values goes to 6 and after this value the total frequency changes very slightly afterward. The relative heights of the second to third peaks decrease rapidly as defocusing values goes to 3 and slightly changes after that
