>>Alright, I am starting to get confused here. I am planning on having a 16:9 screen, you guys are saying you are going to have a 2.35 screen? So what do you do when you have a full 16:9 image?
If you don't have one of these fancy lenses (and most people don't), the best thing is probably to stay with a 16:9 screen and live with the black bars top and bottom when watching a 2.35 movie.
If you have one of these lenses and the right "stretching" capabilities in your system (projector, HTPC, player) then you can get a 2.35 screen and flip back and forth between 16:9 and 2.35:1 pretty easily. It's a question of whether you are optimizing for 16:9/1.85:1 or for 2.35:1.
(EDIT - the following paragraph actually answers your question, the rest is just "background"
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You can also run with a 2.35 screen without the lens/prism if you don't mind fiddling with the zoom and lens shift every time you go between 2.35 and 1.85 content, since with a 2.35 screen you need to zoom out in order to fit the taller 16:9/1.85:1 image on the 2.35 screen. Usually you have to shift the image as well, so it is a pain in the butt.
The decision making process, I think, is :
1. Am I going to end up with a lens/prism eventually ?
2. Can I live with the zoom/shift hassles in the meantime ?
If the answers to both questions are "yes", then get a 2.35 screen. If the answer to either question is "no", then get a 16:9 screen.
One day projectors and DVDs will have 2.35:1 native support (I hear a couple of projectors do already) and this will be easier, but for now a 2.35 system is kind-of on the bleeding edge.
But it gets worse. Do you want to hear about "blended" systems, where you use a custom video processor and 2 cheap 4:3 projectors running side by side to get a 2.35:1 image ?
Such a neat hobby