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SethS: That's pretty much correct. Technically any image generated by or on a computer is CGI, but in practice the term is used almost exclusively to refer to 3D renders. (And nobody in the industry uses "CGI" as a term of art. We're always more specific than that.)
Re the shots in question, I finished watching the director's commentary last night and a surprising number of things in the movie you would assume they did with computers were practical.
A partial list:
•The bombs falling out of the racks in the bomber when Paige Tico triggers them.
•The Jedi hut exploding outward when Luke sees Rey and Kylo together. (Rian said they had wires attached to the set that pulled it apart on cue.)
•BB-8 shooting coins at the guard in Canto Bight, as well as him blowing smoke from the coin slot. The coins were "enhanced" by ILM according to Johnson, but they built a rig that really could do it.
•Snoke's arm and hand when he touches Rey's face.
•The shuttle crash at the Crait base was real. They hired the guy who did the train gag for Inception to make a full-sized shuttle that they pulled through the set.
So, with all that in mind, I have to question if there's as much CG in the close-ups of the saber as people are assuming. I rewtched the scene and there's really only one close-up that requires an actor to be holding it. All the other inserts are of the hand and saber only. No left hand, no body or anything is visible. The only motion aside from the hand moving up or down in frame is the thumb curling.
Personally, if I were designing this shot, I'd have an animatronic hand for the close-ups and avoid as much digitical work as possible. Even if I had to go with a CG hand, I'd find some other way to support the saber so as to reduce the VFX workload. Maybe some kind of rig holding it from underneath, or even hanging it from wires.
Keep in mind that the Gralfex handoff was done with a paintout and digital hand because of the complexity of the handoff motion as well as Mark Hamill being visible in almost every shot. But with the Creepy Uncle, if you hire a guy to hold the saber and then erase the hand, you've removed the only part of the actor that's even in the shot. So why bother with a real hand at any stage at all, then?
That's not to dismiss the issues with the button and the shape of the control box that people have found, but I want to be sure were not seeing what we want to see because of our assumptions as opposed to what's actually there.