How to understand Kepler telescope under large aspherical wavefront
Not sure what you're asking here.  Pretty much any telescope will be unable to simultaneously produce infinity (magnified) output and an aberration-free intermediate focus.  Further, an aspherical wavefront can't be produced purely by a radiating point source (all objects are collections of point sources), so no optical system can refocus an ugly wavefront.  

The way a Shack-Hartmann WFS works is basically not to care about aberrated images. Each subaperture's image is unresolved to begin with, and all the sensor needs is to determine the approximate centroid location.