The invention is directed to a miniaturized optically imaging system with high lateral and axial resolution for endomicroscopic applications. To provide a miniaturized optical head which permits an appreciable increase in photon efficiency with high lateral and axial spatial resolution compared to conventional GRIN optics the plane side of a refractive, plano-convex, homogeneous lens defines a plane entrance surface of the optical system, and first and second GRIN lenses are arranged along the optical axis orthogonal to the entrance surface, wherein the first GRIN lens being arranged downstream of the refractive lens for reducing the divergence of the highly divergent light bundle transmitted from the object through the refractive lens, and the second GRIN lens being provided for adapting the light bundle transmitted by the first GRIN lens to the aperture and object field size of the downstream transmission system.