I understand that in most standard 35mm film the choice of filming in either a 2.4:1 AR or a 1.85:1 AR is up to the director.
With that being said, very recently there's been some IMAX commercials popping up about IMAX films being shown with a 1.89:1 AR as having no black bars and 26% more image. So my questions are as follows:
Does 1.89:1 make that much of a difference compared to 1.85:1?
Is it only possible in an IMAX theater to alternate between aspect ratios or can a director decide to alternate between 1.85:1 and 2.4:1 in a regular theater?