1. An optical imaging system for obtaining a high-resolution image of an observation area from a plurality of low-resolution images, each of said low-resolution images covering the entire observation area, said system comprising: a Cassegrain-type objective for forming said low-resolution images, said objective comprising a primary mirror defining a concave optical surface and a secondary mirror disposed coaxially with said primary mirror, said secondary mirror having a mirror plane and defining a convex optical surface therealong; a focal plane array generally disposed at a focal plane of said Cassegrain-type objective for detecting said low-resolution images therefrom; a microdisplacement mechanism for pivoting as a whole said secondary mirror about first and second orthogonal axes in said mirror plane to displace in a leveraged manner said low-resolution images as a whole between different positions along the focal plane array according to an acquisition sequence, for detection at said different positions; and imaging means connected to said focal plane array for detecting the low-resolution images at each of said different positions and combining said low-resolution images according to a frame generation sequence matching said acquisition sequence to obtain said high-resolution image.