Improved spherical aberration corrector for fast spherical primary mirrors

In the quest to design large and extremely large telescopes, one of the first questions encountered is that of basic optical configuration and shape of the primary mirror. Spherical mirrors have a number of advantages in production, testing and alignment but suffer from substantial spherical aberration, thereby requiring some form of corrective optics. Many designs for spherical aberration correctors are present in the literature, but each has its strengths and weaknesses. We present the design for a new spherical aberration corrector which is believed to offer higher performance with less complexity than previous approaches. The new design is substantially more compact and uses slower optical surfaces than most axially symmetric designs. It can scale to accommodate apertures as large as 100m, and adapts equally well to post prime focus and Cassegrain-like focus applications.