There have been several threads started both here and in the screens forum addressing the issue of moire on a microperf screen at various screen sizes using a fixed pixel display like the new Sharp 12000. Since I have the 12000 and am trying to decide on a screen, I thought it best to try out the projector on a microperfed screen to determine if moire would be a problem at the screen size I am considering. Fortunately, fellow forum member Jeff M. (a/k/a/ TheBland) lives nearby and has a HUGE microperfed Firehawk in his theater. After bribing him with some beer, he graciously invited me over to demo my Sharp on his screen.
What is Moire?
For those unfamiliar with the term, "moire" refers to an unpleasant artifact that occurs when the pixel structure of the projector aligns unfavorably with the hundreds of thousands of perforations in the screen. The best analogy I've heard is the effect you see if you hold one window screen in front of another. Typically the artifact manifests itself as (mostly) vertical lines throughout the image. Because of the potential for moire, screen manufacturers typically recommend a large screen size to reduce, or hopefully eliminate, the problem. The rationale is that as you increase the size of the image, you are increasing the size of the pixels on the screen, hopefully to the point that the individual pixels become sufficiently large to encompass the perforations thereby obviating the moire. A common rule of thumb is anything at or above 110" diagonal will greatly minimize, (and hopefully eliminate), the moire. Since my theater design called for a 110" diagonal screen, I was understandably concerned if moire would be a problem for me. Hence the testing at Jeff's house.
Joining Jeff and me for the testing was fellow forum member Matthew (his handle presently escapes me). Our fisrt experiment: Would moire be present at 110" diagonal? The answer unfortunately is YES. Here is a shot of the moire we saw at that screen size:
http://mywebpages.comcast.net/kirkk/moire1.JPG
Look carefully at the ocean floor and you will see the vertical lines as a result of moire. Here is a close up shot of the problem:
http://mywebpages.comcast.net/kirkk/moireclose.JPG
Here is another shot showing the moire at 110" diagonal:
http://mywebpages.comcast.net/kirkk/arnoldmoire.JPG
In particular, notice the moire on the cooler behind Arnold as well as on his chest and arm.
All three of us agreed that the moire seen at 110" would not be tolerable. So the next question was could we find a screen size at which moire was not a problem? Fortunately, the answer was YES! However the results might surprise you. Somewhat counter-intuitively we found a magic sweet spot at a screen width of 88". I say counter-intuitively because this is obviously smaller than the 96" width of the 110" diagonal image. However, what is obviously happening is that at a width of 88", the pixel structure of the projector is aligning favorably with the perforations resulting in no moire.
Here is Arnold again at 88" screen width:
http://mywebpages.comcast.net/kirkk/arnoldsmooth.JPG
Admittedly, these screenshots aren't the best (I had no tripod) but I do think they are illustrative. We also experimented with increasing the screen size and were able to signifiacantly reduce moire at about 110" wide (126" diagonal). However, we all agreed that 88" wide was actually better. At the smaller width there is no visible moire. At 110" wide it is greatly reduced, although still barely perceptible if you're right up at the screen. If you're wondering if I think I could live with it at 110" wide, the answer is yes. However, that size is simply too big for my room, so I won't be going that large.
Conclusions
I believe that what we saw would be reproducible on all HD2+ projectors. The DMD's will all be the same. So keep that in mind. The other thing to consider is that if you go with a perfed screen at say the magic width of 88" (or 101" diagonal), you may have some problems down the road when you upgrade your projector to say a 1920 x 1080 panel. I still accept the proposition that the higher the pixel count, the greater the potential for moire. That being said, Jeff has very minimal moire (to the point I don't find it objectionable) using his D-ILA on a very large screen. (Help me out here with you screen dimensions Jeff- I forgot them).
Hope this is helpful for those in a similar boat.
Kirk
What is Moire?
For those unfamiliar with the term, "moire" refers to an unpleasant artifact that occurs when the pixel structure of the projector aligns unfavorably with the hundreds of thousands of perforations in the screen. The best analogy I've heard is the effect you see if you hold one window screen in front of another. Typically the artifact manifests itself as (mostly) vertical lines throughout the image. Because of the potential for moire, screen manufacturers typically recommend a large screen size to reduce, or hopefully eliminate, the problem. The rationale is that as you increase the size of the image, you are increasing the size of the pixels on the screen, hopefully to the point that the individual pixels become sufficiently large to encompass the perforations thereby obviating the moire. A common rule of thumb is anything at or above 110" diagonal will greatly minimize, (and hopefully eliminate), the moire. Since my theater design called for a 110" diagonal screen, I was understandably concerned if moire would be a problem for me. Hence the testing at Jeff's house.
Joining Jeff and me for the testing was fellow forum member Matthew (his handle presently escapes me). Our fisrt experiment: Would moire be present at 110" diagonal? The answer unfortunately is YES. Here is a shot of the moire we saw at that screen size:
http://mywebpages.comcast.net/kirkk/moire1.JPG
Look carefully at the ocean floor and you will see the vertical lines as a result of moire. Here is a close up shot of the problem:
http://mywebpages.comcast.net/kirkk/moireclose.JPG
Here is another shot showing the moire at 110" diagonal:
http://mywebpages.comcast.net/kirkk/arnoldmoire.JPG
In particular, notice the moire on the cooler behind Arnold as well as on his chest and arm.
All three of us agreed that the moire seen at 110" would not be tolerable. So the next question was could we find a screen size at which moire was not a problem? Fortunately, the answer was YES! However the results might surprise you. Somewhat counter-intuitively we found a magic sweet spot at a screen width of 88". I say counter-intuitively because this is obviously smaller than the 96" width of the 110" diagonal image. However, what is obviously happening is that at a width of 88", the pixel structure of the projector is aligning favorably with the perforations resulting in no moire.
Here is Arnold again at 88" screen width:
http://mywebpages.comcast.net/kirkk/arnoldsmooth.JPG
Admittedly, these screenshots aren't the best (I had no tripod) but I do think they are illustrative. We also experimented with increasing the screen size and were able to signifiacantly reduce moire at about 110" wide (126" diagonal). However, we all agreed that 88" wide was actually better. At the smaller width there is no visible moire. At 110" wide it is greatly reduced, although still barely perceptible if you're right up at the screen. If you're wondering if I think I could live with it at 110" wide, the answer is yes. However, that size is simply too big for my room, so I won't be going that large.
Conclusions
I believe that what we saw would be reproducible on all HD2+ projectors. The DMD's will all be the same. So keep that in mind. The other thing to consider is that if you go with a perfed screen at say the magic width of 88" (or 101" diagonal), you may have some problems down the road when you upgrade your projector to say a 1920 x 1080 panel. I still accept the proposition that the higher the pixel count, the greater the potential for moire. That being said, Jeff has very minimal moire (to the point I don't find it objectionable) using his D-ILA on a very large screen. (Help me out here with you screen dimensions Jeff- I forgot them).
Hope this is helpful for those in a similar boat.
Kirk
