Interesting post Tony. I was aware of the Petzval lens used for portraiture, but I had to look up the difference between 'achromatic' and 'apochromatic' lenses.

As a photographer (strictly analogue) I was aware of the work of Voigtlander and of Steinheil and of the subsequent manufacturers bearing their names (and who's lenses I use, along with those by Zeiss), but didn't know the Petzval lens was used in astrophotograpy.

Since all of the objects are 'at infinity', you are not interested in depth of field - is this what you mean by "flat field", and why would you need an adapter?