The only time the eyepiece alone may perform as well, is on-axis, in a high-contrast application, as the extra optics of the barlow may cause a slight depreciation. Optically, for all other sues, the eyepice+barlow outperforms the eyepiece working alone. The reason? Most of the aberrations caused by positive spherical lenses (Coma, Astigmatism, Curvature of Field and Spherical Aberration) can be reduced and sometimes almost eliminated by introducing a negative system (barlow) which has the same aberrations in negative quantities! Spherical aberration of the system is reduced as the positive spherical aberration of the eyepiece is cancelled by the negative spherical aberration of the barlow. The other aberrations cancel in a similar way! This is one of the eyepiece designer\'s most powerful weapons, and it is used in most of the shorter focal length ultra-wide designs. Another great benefit of this idea is that the longer eye relief of the longer f.l. eyepiece used with the barlow is retained.