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Discussion Starter #1
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
 

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Kirk,

I have done extensive evaluations of moire on my 125" wide microperforated GrayHawk with 8 different projectors. I have observed "sweet spots" that you are referring to, however, I would be very cautious about picking a screen size in one of these "sweet spots" with the assumption that you will not have a problem with moire. My recent experience with a HD2+ projector showed visible moire at image sizes of about 8' wide or less. Moire was not evident at larger screen sizes. I am surprised about the degree of moire that you observed with a 110" diagonal image (8' wide). It would be interesting to see if you could repeat your observations on a different Stewart microperforated screen. I too found moire unobjectionable at all image sizes when I tested a DILA on my screen. This evidently is due to the higher fill factor of DILA.
 

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If moire is an issue I would recommend Screen Research's products. Their ClearPix2 fabric exhibits no moire. In addition their acoustical transparency is more linear across the frequency spectrum than microperfs.


Chris
 

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Discussion Starter #4
Scott-


I agree that it would be helpful to test the projector on another microperfed screen to see if the "sweet spot" is universal on all Stewart Microperfs. I'm willing to bet it is since I'm assuming the perforation process will be consistent from screen to screen. In other words, Stewart's perfing machine should always make holes that are exactly the same distance apart and in the same pattern. If that's true, the sweet spot should be reproducible on any Stewart Microperf screen. Do you have access to an HD2+ projector to test out the 88" wide sweet spot on your screen? I'd love to see if you could dial it in.


Chris-


You're absolutely correct about the Screen Research screens. However, they are negative gain and quite expensive. I don't know if I would have sufficient luminance at 110" diagonal with the .95 gain of the Screen Research since I recently tested a Dazian Celtic Cloth sample (also .95 gain) at 110" and felt it to be a little dim with the Sharp 12000 in high contrast, economy mode. I realize that the SR may be brighter than the Celtic Cloth due to a different fabric weave, but I suspect the two are close. You can check out the difference between the Dazian and the Draper 1.3 here:

http://www.avsforum.com/avs-vb/showt...hreadid=356874


Kirk
 

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Quote:
Originally posted by Kirk
Scott-


In other words, Stewart's perfing machine should always make holes that are exactly the same distance apart and in the same pattern.
Yes, but is it possible that the material could be rotated some when cut for mounting into a frame? If so, even a slight rotation could produce a completely different grid and moire effects.
 

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Kirk,

I would definitely expect the Stewart microperforating equipment to produce screens with a repeatable hole pattern with respect to hole size and density of the perforations. I am just trying to get a feeling for what you observed. Like I said before I have seen "sweet spots" when zooming the image in and out, however, these are quite specific with respect to image size and I would be worried that it would not be repeatable. The HD2+ projector that I tested did not seem to have any sweet spots when zooming in and out between a screen size of around 9-1/2' wide and 7' wide. Moire was very apparent at the smaller image sizes, but was not visible at image sizes approaching 9-1/2' wide. Unfortunately I no longer have access to this HD2+ projector.
 

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Discussion Starter #7
Art-


That had occurred to me too. However, we moved the projector to a different location during testing and still got the same sweet spot. I'm reasonably confident that when the PJ was moved its "roll" changed a bit too which would be the same as if the screen were slightly rotated in its frame as you suggest. Also, I think Jeff actually tested your theory by tilting the projector different ways and we didn't see any difference. When he's able to post perhaps he can confirm that's what he did.


Kirk
 

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Discussion Starter #8
Scott-


Any chance you can get your hands on an HD2+ projector to try it at 88" wide? There was a little bit of play around the 88" wide sweet spot. For example I distinctly remember getting the sweet spot to work at 87 1/2 " as well. We would move the PJ around or change the size of the projected image and then each time we wanted to go back to the sweet spot, I would just zoom down until the moire disappeared. With each successive attempt at this, we would break out the measuring tape and get 88" wide (or thereabouts).


I would be very interested if any other microperf owners could duplicate this with an HD2+ projector.


Kirk
 

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Kirk,

I will see what I can do. I have had long-term dealings with a local hi-end HT store and am normally able to borrow equipment on short notice. I will contact them and see if they have a HD2+ projector in that I can check out. The main DLP projector lines they sell are Toshiba and Runco. I am pretty sure that the Toshiba HD2+ projector (clone of the InFocus 7205) is not available yet. Maybe the Runco's are out now.
 

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Kirk, Matt, and I had a great time last night. Thanks for the premium beers, too.


No question about it, moire is a problem at 110" on the Firehawk Microperf. 88" is the ideal size (sweet spot) according ot our little pilot study.


We checked three different throws and 88" is it. Playing with the lens tilt did not improve nor degrade the moire, however, it did vary it.


The Sharp puts out a very nice picture even though we handicapped it using an s-video connection. Very impressive!!!


I decided that I have some moire with my DILA but as Kirk confirmed, it is inconsequential - especially relative to the HD-2+ at 110". Fill factor seems to be a direct correlate, more is better relative to the two differnet panels of our 2 PJs.


This wasa quite eye-openning little experiment. A lot of fun.


The other significant conclusion Kirk came to (that I already knew) was that a center channel behind the screen is the best way to set up a home theater surround system. There is no audio / dialog degradation with such (a popular myth).
 

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Jeff,


I'll go you one better. The best center channel speaker is the same as your left/right speaker :)


I'm playing with a 5.1 setup of matching speakers at the moment... quite fun :D


Cheers,
 

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John,


I am better than :D


( my LCRs are all identical SPL Runts from ServoDrive)


Three matched LCRs plus the center smack dab in the middle of the screen = Nirvana
 

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 www.screenresearch.com woven material will solve the moire issue. There should be no dimming of images like the Celtic. Early reviews are saying the opposite. That blacks are better and colors are brighter. Plus you get the benefit of an THX certified acoustically transparent material to put the center channel where it is suppose to be without the use of an EQ.


Vertical centers-matching the left and right


Larry
 

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It seems nice but is almost $4000 for the screen Kirk is looking for (96" wide).
 

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Jeff,


Do you really think I would make a Michigander pay retail?????(I am from Oak Park but now in snowy Chicago) I go there often. To bad Carada does not have miroperf.


Larry
 

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Hmm...good to know t he Michigander thing has some power :D


Can they make these retrofit to a Stewart frame?? (e.g. swap out a Stewart screen so a Screenresearch screen can snap into a Stewart [Electrimask] frame)?
 

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Jeff,


thanks a good question and I have sent it out for an answer.


The ClearPix 2 screen uses a tension method vs velcro or snaps to really tension the screen.


I know that their masking systems should be able to retrofit Stewart screens and you could use the Stewart screen material but then again wouldn't you want an acoutiscally neutral screen???


Larry
 

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Thanks!


Let me know what you hear!
 

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Discussion Starter #19
Larry-


YGM.


Kirk
 

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Try this, I did. It took hours to achieve.


1. Make sure the screen is EXACTLY square. The stewart frame has a tiny bit of play. It could end up being a parallelogram. Not by much, but it doesn't take much. The goal- absolutely straight, level and square perforations. If the perfs themselves aren't square to the frame, then use them, not the frame. This is much harder to do, but with patience is possible and worth it..


2. Same with the PJ. There can be NO keystoning. Not even a tiny bit. Pull out the measuring tape, measure the image at all four sides and square it up. At this point, the screen frame can be used as a reference. If you didn't do #1, then the screen can't be used. The goal here is to make sure the pixels are level and evenly spaced.


Now, you should be able to find a size either right at your frame or maybe overscanned a tiny bit that either minimizes the moire or eliminates it.


I have done this with my 49 x 87 screen and also a 54 x 96.


YMMV though...


Dan
 
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