I wish the movie itself was in that expanded ratio. I wonder if they cropped it to 2.39:1.
I did the math and the Alexa 65’s native AR is 2.1:1. The sensor is just slightly larger and also shaped slightly different from an actual 65mm film frame, which is 2.2:1. So with the Ultra Panavision lenses you get 2.61:1 instead of 2.76:1 like you would with 65mm film.
So, cropping from 2.61 to 2.40 isn’t losing much of the picture, which is probably why they framed it that way. Although, it’s funny to think that La La Land was framed at 2.55:1 theatrically and 2.61:1 for Rogue One would’ve only been a hair wider.
It’s also worth noting that if you crop the sensor to 1.9:1, the default cinema AR, you actually get 2.4:1 with the Ultra Panavision’s 1.25x squeeze. We’re already seeing that same area of the sensor used with spherical lenses to shoot in “digital Imax” such as with the airport scene in Captain America: Civil War and the entirety of Avengers 3 and 4.
Anyway, I think it ultimately comes down to the fact that 2.4:1 is a standard AR while 2.61:1 isn’t. Probably also to match with the other Star Wars movies.
I’m curious how Han Solo is going to look. It would be fun if they surprised us with the first 1.85:1 Star Wars movie.