Originally Posted by miltimj
Awesome solution, guys! If there's ever step by step instructions (especially including the "what I would have done differently" part of it), this is AVS Hall of Fame worthy!?
Thanks. The project has been fun... and frustrating at times. Having this thread has kept me going. The input from everyone has made it a huge learning experience for me.
Originally Posted by miltimj
Scott, one question regarding the 4-way vs 2-way system. Am I correct in my reading that the only reason you had to do 2-way is due to the projector/lens/scaler combination you used, and that it changes the height slightly? Is there not a relatively simple solution (different scaler, etc) that would have negated the need for horizontal masking?
There are a number of reasons I went with 4-way rather than 2-way.
First, I actually built my screen and masking before I bought my projector. Even though I knew what projector I wanted to buy and had done all of the calculations on throw distances, I still wanted the fudge factor that the 4-way masking would provide.
Second, I want my theater to have some level of "future proofing". I know I will update my projector over time, and I want flexibility in case a new projector has different throw characteristics. I don't want to have to rebuild my screen wall for a new projector in the future.
Third... (this one will probably be a little controversial and most likely deserves its own thread. I have thought about starting a thread on this subject, but I'm a bit too busy right now)... After having my setup for over a year, I've come to the conclusion that for most of us a 100% "Constant Image Height" (CIH) set up is a pipe-dream. The reason is that it is not practical to scale, stretch, and/or zoom all aspect ratio formats to always fit a constant height.
The easiest example for me to try to explain this is in the case of an aspect ratio of 2.40:1. (Bear with me here. If you don't like math and numbers, this will get boring). Let’s start with a 16:9 screen that is 51” tall and 90.7” wide. In native format with no scaling or stretch, a 2.40:1 movie will fill the width, but will only be 37” tall with black bars on the top and bottom (90.7 / 2.4 = 37). If you are using the horizontal stretch method to accomplish CIH, you must first vertically stretch the image using a scaler. Here is where the first problem arises. In order to fill the CIH of 51”, you must vertically stretch the image by 37.84% (37” X 1.3784 = 51”). For me, I am using a Panisonic AE-1000U projector to do the scaling. It only has one vertical stretch mode, which is fixed at 33.33%. This means that I cannot stretch a 2.40 movie to fit a CIH of 51”. My projector will only stretch it to 49.3”, therefore I STILL have black bars of about 1” at the top and bottom of my screen. Now, if you have a very expensive scaler or you run your movies through a Home Theater PC with the right software, you might be able to vertically stretch the image by a customizable ratio which would fill the image height of 51”, but that does not fully solve the problem. You still must horizontally
stretch the image to fill a 2.37 screen (120.87” wide in this example). To do this, you must have an anamorphic lens. The problem is that almost ALL anamorphic lenses are FIXED to stretch the image by 33.33%. So even if you could vertically stretch the image by 37.84%, you would still have a slightly distorted image if you horizontally stretched it by only 33.33%. In my case with a fixed vertical stretch option, I could use a combination of an anamorphic lens with the “zoom method” to fill screen, but my projector doesn’t have zoom memory like the Panny AE-3000U. And even the Panny AE-3000U only has one zoom memory option and you would need several for all of the various possible ratios.
Another tricky situation for CIH is the 1.85:1 aspect ratio. On a native 16:9 screen (51” X 90.7”), the width would be filled, but the image would only be 49” tall (90.7 / 1.85 = 49"), leaving black bars on the top and bottom of the image. To technically have a correct CIH image, you would have to vertically stretch the image by 4.08% and then have an anamorphic lens that would horizontally stretch the image by 4.08%. To my knowledge, there are no such lenses available. You could of course use the zoom method, but some CIH purists don’t consider the zoom method to be an ideal option.
While the above examples can be overcome with a fair amount of customizing at the start of each movie, I’m not too interested in spending a lot of time and money on fancy scalers and having to try to mix both the zoom method and the anamorphic lens method in order to achieve true CIH. For me 4-way masking is a better solution which also meets my other needs mentioned above.