Originally posted by repaap Well, I’d like to have 20 or even 18 mm small prime with not much distortion, unlike voigtländer.
Well, distortion is corrected by a lot of glass, so that rules out small for an ultrawide, Repaap.
I note that Nikon have a 20mm f1.8 on their roadmap. It will be a good big lens, or a weaker small one, up to the designer.
Lenses around the natural registration distance, the 35 to 55mm range, don't need a lot done to them. Longer than that is harder, and wider is hardest of all, as Roger Cicala says.
It's no surprise from a difficulty of design point of view, ignoring marketing, that the DFA* primes will probably come out in the order 50mm, 85mm, 35mm, and twentyish.