The cost of astrographs with pupil diameters greater than 1 or 2 meters can be somewhat reduced if the primary mirror is made spherical and the aberration corrected at or near the prime focus, thus avoiding the classical Schmidt or Maksutov full pupil diameter refractive components. Such a corrector solution is presented here for large spherical primaries with speeds up to f/4. This is based on the "KiwiStar" principle presented here in 1997, in which a large spherical-concentric catoptric is combined by pupil transfer with a smaller spherical-concentric catadioptric to give well-corrected wide-field images of high speed and broad passband. The designs studied at the time were limited to those with entrance pupils <2m diameter, but it has been found possible to extend the aberration correction capability to pupils of larger diameter. The only significant constraint found in the present study is that the spherical aberration of primaries faster than E/4 is difficult to control. The design presented here is a 4m entrance-pupil-diameter, f/1.4 optic of 0.2 arcsec rms resolution over the whole of a 0.5<degrees> field (50mm diameter), for a bandpass of 486-850nm. To fully sample this field would require 108 pixels of 5 mum dimension. An extended design with an sm diameter primary is also shown, that may be scalable to similar to 30m. To achieve this performance, the strictly concentric format of the original "KiwiStar" design has been relaxed, thus providing extra degrees of freedom to compensate the large pupil aberrations introduced by the spherical aberration of the primary. Nevertheless, the new design still has only one relatively small and weak aspheric surface to provide zonal correction, all other surfaces being spherical.
