Exactly why I bumped this thread, to ask if anyone had experience with this specific pairing. So far no, but it seems from Phil's quite broad testing that a small but real improvement could be expected with the 20/1.8 prime. I understand that it won't compare to water contact options (which are not options for me anyway due to cost an compatibility) but it also sounds like it punches above its weight class for the price. And those small gains may occupy a sweet spot, if it pushes the middle apertures into useable territory. I would still love to hear from (if) anyone who has tried this correction lens on the 20/1.8 though!