Ah, spherical aberration! Not chromatic aberration, d'oh! Thank you! Found it: "General formula for bi-aspheric singlet lens design free of spherical aberrat

Ah, spherical aberration! Not chromatic aberration, d'oh! Thank you! Found it: "General formula for bi-aspheric singlet lens design free of spherical aberration" https://opg.optica.org/ao/abstract.cfm?uri=ao-57-31-9341 https://opg.optica.org/ao/abstract.cfm?uri=ao-57-31-9341 https://petapixel.com/2019/07/05/goodbye-aberration-physicist-solves-2000-year-old-optical-problem/ https://petapixel.com/2019/07/05/goodbye-aberration-physicis... https://phys.org/news/2019-08-physicists-year-old-optical-problem.html https://phys.org/news/2019-08-physicists-year-old-optical-pr... https://news.ycombinator.com/item?id=20369960 https://news.ycombinator.com/item?id=20369960 and https://news.ycombinator.com/item?id=20703140 https://news.ycombinator.com/item?id=20703140