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I was just re-reading this thread a little and I thought I'd mention that my local Regal Multi Plex theatres uses no masking. They just change lenses. The screen remains the same width, but the highth of the image changes. Just like us using a 16.9 projector, only it's film of course. So, the scope films are shown with the top and bottom not hitting the whole screen. Why they don't bother with masking is probably just that they are cheap and lazy and 90% of the audiance doesn't really care. Our theatre, the theatre featured in the movie, the Blob with Steve McQueen, does use masking. It's Manual. I have to walk down to the stage and change it by hand. The Highth stays the same, but the image gets wider.

Another thing I might mention is Movie Theatres mostly use 1.85 and 2.39. 1.85 is almost 16.9. Those films are actually masked in the projector and blown up bigger to fill the screen. Most of the films come hard matted. The image on the film frame is already masked. You are using only maybe two thirds of the entire 35mm frame. It's a cheap way for theatres to give the illusion of a bigger screen, but it's actually less resolution than scope or the older 1.33 that use the entire 35mm frame.

I contend that, if you have the money, the space and the time, go ahead and reach for that ultra perfection. If you don't, or you are an old fart like me who just wants to watch no fuss movies, use a 16.9 screen and just live with the lower res of letter boxed DVD's. I also remind you, used 16mm and 35mm scope lenses are on e-Bay very cheap sometimes. I got a box of 5 lenses for $15 once already. And of course Blue Ray will change these dynamics.