Hi David... With ISO 400 film, it's easier; I can manage f/4 at 1/30 for a typical office/business interior. Of course there are darker circumstances too, dim restaurants etc. But consider the ISO 100 film just means cranking the lens open another 2 stops in that store, so there you are at f2 and 1/30, no problem. This is what fast lenses are for.
🙂 And then open another stop to f1.4 if needed, and a venture to 1/15 in reserve.
Dental assistant put on her own lead apron when I told her I was radioactive already and didn't need it!
Zeiss Ikon camera with 2/50mm Voigtlander Heliar Classic, Kodak UC100