Prisms or prism systems in optical systems are used in different fields of science and engineering very frequently. Their technological deviations (e.g. degree of deviation between sides, etc.) induce an image doubling. In this paper we present a detailed analysis of the image doubling influence on the Modular Transfer Function (MTF) of the optical system. Relations that enable to determine the acceptable technological tolerances of optical prism elements so that allowed image doubling does not create the unacceptable decrease of MTF of optical system under a test are derived.