Vic Chapman
Forum Pro
It isn't about 20mm it is close to 24mm. If you want around 20mm you need the 14mm f2.8 which is equivalent to 21mm. That is a big difference when you look at pictures taken with them.I went for the 16 because in 35mm equivalent it is about 20, my favourite focal length according to my shootings statistics. I also took a samuang 12, just in case I needed something wider. But that has happened much less than I anticipated.
the best would be to use you shooting history to see if tha zoom makes sense, assuming you ever had something that wide to get meaningful statistics.
Vic