| We investigate a family of two-mirror correctors to compensate the aberrations of a parabolic mirror (f/4.5 to f/6) observing at a large angle from the zenith. As a first approach, for regions of up to 22.5 Deg off-axis, we investigate a system of two decentered & tilted aspheric mirror correctors with bilateral symmetry. A second approach, for regions of up to 7.5 Deg off-axis, taking into account the field of view distortion control, the secondary and tertiary mirrors are warped using Zernike polynomials which we know can be generated with active "vase" mirrors.;The performances of these corrector designs are useable for imagery, i.e. image quality is close to the seeing limitation: 80% of encircled energy diameters of 0.5-0.8 Arcsec, and a field of view of 12-18 Arcmin. |
