Corona physical material gives you an option to chose between specular and IOR modes, unfortunately this functionality hasn't been ported back to old materials, like legacy, or skin, so i'm looking for a tool to convert specular textures to IOR. After some research i found this
topic by Dubcat. Since i'm using 3ds Max 2016, i don't have access to OSL, so i had to use his LUT file in Affinity Photo to convert textures externally (which is preferred method for me anyway). The problem is, that i couldn't manage to get correct results with it - it's either i don't know how to use it properly, or Affinity treats this LUT somehow differently.
Then i found this
tool by Mohammadreza Mohseni, but virus total flagged it as malicious, so no use :/
At this point i'm out of ideas, so any help would be greatly appreciated.