Go to google, click on groups, search or otherwise

If that link is garbage (doesn't look too alive when pasted), go to
And search for
Metrogon cell spacing revisited HELP

Brian Caldwell responded. He wrote one of the major optics design programs AND made his own 11x14 Topogon (predecessor of the Metrogon, but follower of Hypergon). He explains why it can be done with relatively cheap variety of optical blanks, discusses some problems he had, but he's no amateur...he does seem to think it was not a big deal. He didn't say how long it took, or what his perspective for inexpensive means (compared to paying someone to do it?)

I think the achromatizing on that design (oops, I'm diverging to Metrogon again) was accomplished thru the degree of symmetry), and other aberrations corrected thru symmetry and aperture reduction (you don't see smaller f/# than 6.3 to my knowledge on Metrogons. I don't know about Topo- or Hyper- types)

I can link you to the patents on Metrogon Topogon and an English variant that might not have been commercially popularized.