Nick,
The problems with most 1080P projectors is lumen output, which is the reason high gain screens are becoming popular. Not many have much, or can compete with 720P units. Some are getting close though and I suspect in a year most will be on par. You want a minimum of 12 FL to give you that “POP” for movie watching and good shadow detail, and should up that number to 20 FL for sports. If you will have ambient light, then figure at least 15 FL and 23 FL respectively. Another consideration is projector rated lumens, which are always ridiculously generous. After the projector is calibrated to a D6500 standard, lumen output is drastically lower than rated output. Also figure a 50% loss within 500 hours of use and another 20% before it finally dies on you. My PT1000 for example has roughly 200 lumens after I calibrated it with 1200 hours on the bulb, but it’s rated much higher (900 or so I believe). I’m shooting onto a 96 X 41 2.35 screen. This equates to roughly 9.5 FL with my 1.3 gain screen. Figure another 10% loss shooting the beam through the anamorphic lens and I’m just over 8. That is a dim picture and I can’t stand to watch much of anything unless the room is completely dark. If I were using a screen with a gain of 3, my net FL would be about 19 FL and I could, if I want – watch movies with some light on. By having excess FL, you have many options available to you for really dialing in a perfect picture as well. ND or colored lenses for one. You also have plenty of wiggle room for bulb output fall off as more hours are put on it. If the picture is simply too bright, just use an ND lens and as the bulb dims, you ditch the lens.
So, yes, you are correct. High gain screens help compensate for projectors with low lumen output and are also desirable for set ups where ambient light is a problem or if you like to watch sports or movies with some light on.
In regards to improving contrast, gain doesn't help a whole lot. It allows you to run propper contrast / brightness controls without runing them to extreems for improved shadow detail. Silver and grey are great colors for screens because it enhances contrast and rejects ambient light, but typically, silver, and grey come with a penalty – they have a negative gain.
If you will be using a ‘smallish’ screen, the math will look much better for a projector with low lumen output. As the size increases, the math starts looking poor quickly. Another aspect is throw distance. If you are at the long end of the throw, lumen (reflected) output is reduced. The closer to the screen the projector is, the brighter the picture will be.
If you know exactly what the screen size is, lighting environment, room wall and ceiling color, throw distance and if sports will be watched……that will help determine what type of lumen output you need and if a high gain screen is needed or not.
More often the not though, a high gain screen is desirable. One drawback is they tend to have a narrow viewing cone or require the projector to be mounted in some odd angle or directly onto the screen. From what I've heard about the Prismasonic, they may have come up with a dandy. Definately worth looking at a little closer.
