A Canon 20 f1.4 would obviously be a huge and expensive lens. I would prefer a cheaper,, and smaller 20 f2. But, likely not see either in EF mount. That would still be fast enough for astro photography especially since bumping up the ISO works very well on cameras these days. So why does Canon make these very fast and very good RF lenses which are very expensive. Do they make more money on them or is it simply for prestige or one-ups-manship? If I had no equipment, starting from scratch, I would go to Nikon mirrorless because of their 20 f1.8...which is neither compact or cheap. I am not a troll, pretty well satisfied with my current Canon equipment although no plan should my 6D need replacement.