Lastly there is also a manual shutter control, which stops down the lens. Since I was working with large screens, I left it open all the way, but this could be handy if you are in an environment where the projector is overly bright. (It is one of the brightest home theater projectors I have worked with, having more "horsepower" (lumens) than the Panasonic PT-AE900u LCD home theater projector (in full power, dynamic iris on), the Marantz, VP-12S4, and the Optoma H78DC3 (in Brite mode). The BenQ projector is rated 1000 lumens, which isn't particularly high, but it does seem to be brighter.
Choosing a Screen
I just love this projector on my 128" Stewart Firehawk, however if you have darkened walls and a dark room, and a smaller screen (say 110" diagonal), a matte white surface should work fine. If you are going under 100" diagonal, you can stick with the matte white, and rely on the shutter control if your image is too bright. The BenQ projector has plenty of contrast, and excellent black levels, so I don't think a high contrast dark gray screen (like a Stewart Grayhawk) would be necessary. (BTW, the Firehawk works well in rooms with side ambient light as it rejects a good deal of the side light, as you can see in this daytime shot of my theater room (new shades and room painted dark are coming in the next couple of months. Just out of site is an upper window that is responsible for the washed out area on the top right of the screen. In the second picture, I have adjusted the exposure, so you can appreciate what the picture looks like with that ambient light in the room, however it does make the walls look much darker.
BenQ Projector Noise Levels
BenQ rates the projector at less than 26db in full power mode, and below 23db in low power mode (Lamp at 200W instead of 250W). The projector sounds a bit noisier than a couple of other HT projectors with similar specs, but not by much. More importantly the fan noise is unusually low pitched compared to most, and that makes the fan noise less noticeable. This is a very quiet projector, quiet enough to be a non-issue.
BenQ rates the PE8720 lamp at 2000 hours in full power mode, and 3000 in low power mode. I expect most people using 100" diagonal or less will be able to run in low power mode, and save some bucks.
The BenQ PE-8720 is a typical high end DLP projector with a 5X 6 segment wheel. As I understand it, there is no difference is one's susceptability to the rainbow effect between projectors with 6, 7, or 8 segments. It's the 5X speed that's critical. Only a very tiny percentage of viewers will ever notice the rainbow effect with this projector even rarely, and even less will find it to be an annoyance. (Of course if you are the one....you'll need an LCD projector.)
Don't even think about worrying. Perhaps it's because this is such a large projector, and they have plenty of space to baffle the sound, and the light. Two very dim lights on the top panel are all you have to deal with, and they are as dim as you could hope for.
Lens Throw and Lens Offset
The PE8720's lens is longer throw than their PE7700. The projector will fill a 100" diagonal 16:9 screen from as close as 13.0 feet and as far back as 17.75 feet. With that 100" diagonal image, if you are ceiling mounting the BenQ projector, the lens offset will allow the center of the projector's lens to be approximately 4.9" above the top of the screen surface (or 4.9 below the bottom when table mounting). Lens shift allows you plenty of flexibility if you wish the projector mounted lower (from ceiling), or on a shelf.