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Author Topic: Non perf screen Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 03-29-2012 04:44 PM                     If I turn the projector on it's side, it completly goes away. Maybe I'm thining about this wrong, but what if I order a screen and reverse the height and width and then rotate it 90 degrees......  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 03-29-2012 11:22 PM                     What is the minimum angle do you have to rotate the projector with respect to the screen in order to make the problem go away or, at least, be less noticeable? Sometimes it's only a few degrees one way or another.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 03-30-2012 12:36 PM                        The so-called "acoustically transparant" screens have been around for quite awhile -- they are basically made using a very fine layered woven plastic material -- picture a wicker basket. One layer of the weave is on top of the other so no holes show, yet sound isn't blocked (much). Problem is, so far, I am not aware that they make this stuff in more than 15 ft widths. Seems it would be a great market if they could manufacture it for commercial cinema use. Only trouble...so far, I have never see this material in a silverized version, but that doesn't mean it couldn't be made (Brad?). As for the issue at hand, Richard, a down and dirty, albeit a work intensive fix is based on the projector tilt concept. If you can live with a slightly smaller screen image, you could "tilt" the screen. Basically restring it so that it is not sitting parallel to the frame. In other words, pull one corner closer to the frame than the other causing the screen itself to be sitting crooked in the frame, assuming your frame is somewhat larger that the screen fabric as most are (usually about 6 inches to a foot). Then you adjust the mask so it frames out the off-centered screen. This in effect will skew the perfs and HOPEFULLY eliminate or at least lessen the moire problem. Only downside of this will be that you will have to reduce the image size a bit to compensate for the off center tilt. Another solution, since you say you are actually able to eliminate the moire just by placing a white material behind the screen right up against the perfs, you might want to try a piece of white china silk. That is pretty close to acoustically transparant and it might do the trick in term of both letting the sound thru and still killing the moire. The problem might be that it is not a rigid material and it may be difficult to keep it in close contact with the screen. It would be the same as pressing a piece of foamcore against the screen. As for a non-perf screen....no way will you be happy with that. In fact, I would say it's out of the question. As for figuring out perf size vs projector pixel size, evidently that CAN be predetermined because there is one home theatre screen manufacture who asks for the projector make and model so they can perf their screen material at a specific pattern to eliminate moire, optimized for that particular projector (or so they say).  |  IP: Logged Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 03-30-2012 01:02 PM                        As we're talking digital, could you just tilt the projector a few degrees and then use keystone correction?  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 03-30-2012 01:18 PM                        Wouldn't keystone correction just rearrange the pixel pattern so it again matched the perf pattern? I guess, it depends how much tilt would be needed to eliminate the moire. If just very slight, that would be much easier than tilting the screen materal. On the other hand, it would have to REALLY be a slight tilt; seeing a skewed image on the screen is pretty awful if it is noticable, and I'll say this, if I see credits not perfectly parallel to the screen edge, I have to up my meds.  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 03-30-2012 05:09 PM                     Randy and Martin......It took much more than a few degrees before it went away. The only way I see, other than "trying" a different type of screen, is to put something up against the back like Frank says. Or like I said, order a regular screen and turn it 90 degrees.....I can't see why that won't work if by turning the projector 90 degrees, it goes away.....  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 03-30-2012 06:41 PM                     How far of a turn? Like 45 degrees? I don't know if this will amount to anything but I'm thinking about this problem to see if we can puzzle something out. Basically, a Moire pattern is a visual beat frequency: Play two audio tones at the same time and you hear a pulsation that varies in proportion to the frequency difference between the two. Superimpose two visual patterns and you'll see a "pulsating" pattern of waves corresponding to the difference between the size/distance/period of the two patterns. If we know the beat frequency between two sounds and we know the frequency of one of the sounds, it is possible to deduce the frequency of the unknown sound. I don't know if this is possible but let's ask the question: If we know the dot size/resolution of the projected image and the amount needed to turn in order to make the patterns go away, is it possible to deduce something about the screen, the picture or the relationship between the two which can help us change some variable that will make the problem go away?  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 03-30-2012 06:44 PM                     I will have to do it again but I think it was at least 45 degrees.....probably more. If everyone lays on the floor, I could keep the projector 90 degrees.....  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 03-31-2012 06:15 AM                     Your perf pattern sound like it is off set 50% row to row in an alternating layout....a moire producer at the right resolution.  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 03-31-2012 08:38 AM                        quote: Richard Fowler Your perf pattern sound like it is off set 50% row to row in an alternating layout....a moire producer at the right resolution. Ah...now we're getting somewhere. Is that how you tell if a particular screen will be a problem? And do they still make new screens this way, or have the screen manufacturers changed perforation patterns since video has become common in theatres?  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 04-18-2012 12:37 PM                     The microperf screens came in. I installed one this morning. The pattern is totally gone now. That was the way to go.  |  IP: Logged

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