We present some results of the attestation of the coude optical system of the 2-m Terskol Observatory telescope by Hartmann's method. All of the Zaidel aberrations (the spherical aberration, coma, and astigmatism) exist in the wauefront. On eliminating the aberrations by performing the adjustment for the telescope, the value d_0.8 = 1" (energy concentration is 80 %) can be achieved for star images. The presence of the triangular astigmatism in the residual aberrations which is prominent on the wauefront map can be explained as a result of the flexure of the tube and telescope unloading system. Our analysis of caustic curves shows that small-scale errors of the wavefront play the main role in the image degradation.