I'd like to give a go at explaining the preference for CIH over a regular Constant Image Width set up, in terms of RBP's questions. I think someone
new to CIH height can hear people say they simply prefer their CinemaScope
images wider than 16:9 images, but not really "get" or feel the reason why
this would be such a big deal.
As people have pointed out, the issue is about the relative impact of
one film aspect ratio/image size vs another. That's the very important element to keep in mind.
It's understandable to think "Well, if I have 120" of width to work with, why wouldn't I buy a 16:9 screen? My 2:35:1 CinemaScope movies will be as big as I can have them in my room, and so will my 16:9 images. In buying the 16:9 screen I'll be maximising the impact of both aspect ratios, insofar as both aspect ratios will be as big as I can possibly get them in my room."
Yes, that's true. When looked at "individually" given the 120" width restriction, you maximized the visual impact of both aspect ratios.
But that does not take into account RELATIVE IMPACT: that is, what happens psychologically when you view images of varying sizes.
You might have a projection screen that seems pretty big. But spend a while over at a friend's house who has a much bigger screen and when you come home suddenly your screen is going to feel pretty small. Same as if you watch the image on your wall at 100" diagonal, then for a few movies zoom the image to a much larger 120" diagonal, when you zoom back down to your 100" diagonal what seemed "big" before will now seem smaller in comparison with the images you just watched and hence have the feeling
of having less visual impact because it feels smaller on comparison. By this you should see that the impact of an image is not so simple as it's sheer size; the impact of an image, whatever it's size, will be affected when you compare it to an image of another size.
This is an unavoidable phenomena and it is the crux of why people go CIH.
When you buy a screen of a fixed aspect ratio, be it a regular 16:9 screen or a 2:35:1 screen, you are choosing to maximise the relative visual impact of one aspect ratio over another. With a 16:9 screen you will be maximising the relative visual impact of 16:9/1:85:1 images over CinemaScope 2:40:1/2:35:1 image. Everytime you go from a 16:9 image to a CinemaScope image, the CinemaScope image will look (and be) smaller - the comparison to the 16:9 image will rob the CinemaScope image of impact - just as if you'd been used to watching a big screen and reduced your screen size.
The same will happen if you choose a 2:35:1 screen. It will maximise the relative impact of wide CinemaScope movies, but 16:9/1:85:1 movies will appear smaller on the screen and hence have less relative impact than the
So it's about choosing which movie format you think should have the most cinematic impact over the other. Traditionally, cinemascope had, and is supposed to, have the "greater" impact so far as producing a wider, grander vista for the eyes. Which is why so many epics used the format, to give that feeling of size, sweep and grandeur. CIH devotees feel this is the way to go: they like the CinemaScope movies to have the most impact - Ben Hur and Lord Of The Rings should feel more Special Event than The 40 Year Old Virgin.
So remember: the Comparison of image size that naturally happens when you are switching aspect ratios will affect the viewing experience.
If you have a 120" wide 2:35:1 image it will feel really big and wide and cinematic. But if you go from that to watching a 120" wide 16:9 image that is much bigger, the 2:35:1 images will not "feel" so big anymore because of the comparison. What once was impressive is now made less impressive, what once felt huge no longer feels huge, because you've introduced the constant comparison with an even bigger (16:9 image). Whereas if you have a 120" wide 2:35:1 image and move to a narrower 16:9 image the 2:35:1 image will always maintain it's impact, it will continue to feel grand and impressive.
So the issue of visual impact is not strictly about image size alone - about making every image as big as possible. How our brains interpret the feeling of "size" and "impact" is very influenced by comparisons that will make one image, which could have felt "big" look "small" if we go comparing to another image.
Lovers of CinemaScope images and CIH devotees in general understand this phenomenon and use CIH set ups to keep the visual impact of CinemaScope films greater and more "majestic" in comparison to narrower aspect ratios.
Add to that: 2:35:1 shaped screens just look cooler than run-of-the-mill 16:9 screens, and the expansion of an image from 16:9 to super-wide CinemaScope is a very impressive experience as well. In a hobby that is so much about psychological effects, such experiences shouldn't be discounted.