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Discussion Starter · #1 ·
Hey there Vern (and anyone else who wants to jump in here). As I threatened in the other thread, I am starting a new thread to hopefully get some answers about my setup. It has been a very crazy couple of days around my house and I have not set foot in my HT to take a picture of my issue, but I found a picture on a screen shot thread that has EXACTLY the same type of lines I get with my ISCO III. It is only noticable on bright scenes. I stole this pic from another thread so thanks to the OP over there for accidentally capturing my issue.
I should add that the picture is somewhat exaggerated over what I am seeing but it is the same thing. I could not figure out how to put the picture on the post directly so it is attached.


To recap my setup for you: Projector is a Titan HD-250 from DPI, ISCO III lens, 2.40:1 Harkness Hall mini-perferated screen with a gain of 1.5 and if it matters, a port using optical glass to separate the booth from the theater. Thanks!!!!!
 

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Chris, is your screen AT by chance? It looks like moire (spelling?)...


Mark
 

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Quote:
Originally Posted by CAVX /forum/post/15530169


Chris, is your screen AT by chance? It looks like moire (spelling?)...


Mark

I think you're exactly right - he said his screen is a "mini-perforated" Harkness-Hall. I just put my first AT screen in and was surprised at how much I had to rotate the fabric to eliminate moire - anywhere between 15°-30° depending on your material (I used SW4500).


My question is, does a mini-perf like the kind Harkness-Hall uses also cause moire as compared to a weave-type AT screen like SMX or SW4500? If so I would imagine the company would ship the pre-cut screen matieral with the perfs running at an appropriate angle. TSHA222, can you give us some more info on your screen and the perf material's orientation?
 

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Quote:
Originally Posted by HogPilot /forum/post/15530990


I think you're exactly right - he said his screen is a "mini-perforated" Harkness-Hall. I just put my first AT screen in and was surprised at how much I had to rotate the fabric to eliminate moire - anywhere between 15°-30° depending on your material (I used SW4500).

And I am sure I had to go past 30 degrees with mine. I also think that there is minimum sizes that screens can be to work as AT, where the larger the screen, the greater the pixel to perf size and therefore I would think, less chance or moire. Maybe someone else can better explain that, but having installed larger ATs than mine (upto 130"), and a simple 10 - 15 degrees was all that was needed and there was no moire to be seen...

Quote:
My question is, does a mini-perf like the kind Harkness-Hall uses also cause moire as compared to a weave-type AT screen like SMX or SW4500? If so I would imagine the company would ship the pre-cut screen matieral with the perfs running at an appropriate angle. TSHA222, can you give us some more info on your screen and the perf material's orientation?

I've seen it on a Mircoperf as well as a woven fabric and I really think it comes down to pixle Vs hole size...


Mark
 

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Quote:
Originally Posted by CAVX /forum/post/15530169


Chris, is your screen AT by chance? It looks like moire (spelling?)...


Mark

Well, the screenshot is from somebody else and we don't know if that person has an AT screen.


Looking at the posted screenshot, it appears that the lines are also on the hand holding the gun in front of the screen - so probably not moire.


Maybe those are Newton rings (interference artifact from non-parallel elements)?
 

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I know that look very well...That swirlly, fringey looking pattern.....MOIRE!!


Been there before.

2 ways to deal with it.


1. De-Focus your projector until it disappears (slight).

2. Have the screen re-made in a way that rotates the perforation pattern a few degrees. Before I ordered a Stewart Microperf, they sent out a kit with a piece of screen material that was able to be rotated like a pin-wheel 360 degrees.You fire up the projector, aim it at the material and with a protractor, measure the angle of the perforation pattern vs vertical (0 degrees) as you rotate the screen material on the pin wheel apparatus. With the perforation pattern in its normal (vertical) configuration, I needed to change the angle of that overall pattern 17 degrees to make a perfect, moire free projector. Different projectors may require different perf screen angles. Stewart, as a matter of course, asks for the projector model in the ordering process... they have many projector's perf requirements in their data base.


My screen is a scope, 2.4 shape that is 168" wide (14').. So, they can do this on large sizes.
 

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I really don't think it moire (at least in the screen shot). Moire is a beat pattern that generated when the projected image has a single frequency pattern that's close to, but not exactly matches, the spacing of perforations on the screen. The key is moire is a due to a combination of both the projected image and screen.


But the screenshot shows that the lines are being projected on the guys hand - it must originate from the projector/lens. It's also hard to see what the image is, but it appears to be pretty wide vertical bars; not the type of image that would generate moire.


TSHA222 - do you see the lines on all content? Or just on certain images?
 

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The hand is part of the picture / video and the patterns extends from the hand to the background.... It's looks identical to the moire issues I have dealt with.


If the poster has an extra piece of screen material, it would be easy to test my hypothesis.
 

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Quote:
Originally Posted by ilsiu /forum/post/15531471


TSHA222 - do you see the lines on all content? Or just on certain images?

I understand what your saying, but I think TSHA222 has posted that as an example of what he is seeing on his screen. I only ever saw the green and purple (or is that magenta?) lines after I got an AT screen, and then I had to work out how far to turn the fabric to get rid of them. I would see the lines on bright whites and flesh tones. Hopefully out OP can inform us of his exact circumstances now a few have piped in with suggestions...


Mark
 

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Yep, looks like moire. Simple test: hold up a sheet of white typing/xerox paper against the screen surface and see if the moire pattern shows up on the paper. One other possibility would be newton rings, but I highly doubt it. I have never experienced this problem as I prefer to stay away from perfed screens in my HT.


Vern
 

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Discussion Starter · #11 ·
Wow, I go away for a bit and everybody posts! Now I have a name for what I am seeing! OK so to answer a few questions, my screen is perfed and it is not "rotated". The perfs are pretty much in a grid pattern. I don't get the "moire" unless the ISCO is in the path. I can change the location and intensity of the moire by shifting the lens, rocking the focus or even zooming. After redoing everything over the weekend, I have the issue somewhat subdued I can in fact eliminate it totally by defocussing.


I have a non perfed screen that I can throw together and place in front of the AT screen to verify if the pixels are causing this. The perfs are not visible unless I get much closer than I sit. The pixels are barely visible from one row and disappear for the second. One thing, and I know I am going to get harped on, my projector is a 720p so the pixels are big for a screen size like mine, but I built with the intention of upgrading to 1080p when it gets more affordable.


I do see the pattern on all sources but only if there is a bright image in the scene like snow or sky, otherwise it is not noticeable at all. Thanks for all the input. If there is anything else I need to check, let me know. I have been living with the image defocussed and while that is not totally ideal, it is not the end of the world, either.
 

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Nope, you got it... But just put up a white piece of paper against the screen rather than constructing a temp screen and you'll see the moire disappear where that paper is. Use a white image (or the image you posted).


Yes... 100% moire.
 

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Discussion Starter · #13 ·
Is this an issue when you have AT screens and anamorphic lenses or are there other instances where it can rear it's head? And thanks again. I actually have it now where the de-focus is not so bad where before, I had to really de-focus much more to eliminate.
 

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It is perf screen induced. Just rotating the perf pattern can eliminate it... Next screen you order, get a sample with a protractor and you'll know exactly how much is needed. It is based on the PJ panel, lens and perf arrangement and alignment. All factor in.


This happened to me with a Panamorph AND ISCO lens on 2 different screens.
 

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Discussion Starter · #16 ·
OUCH. A New screen will not be right away but I guess it is needed! I wonder if Harknes Hall has the ability to understand what it is I need. I am very pleased with their screen and it was very affordable. Thanks again folks. It's always nice to get confirmation that you are not a complete idiot.
 

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Glad we solved it... Good luck!
 

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Discussion Starter · #18 ·
Me too. Now would it be too off color to request we pass around the collection plate? lol
I am calling Harkness to see if they know what needs to be done to correct this on another screen order, otherwise I guess it's off to do business with one of the big guys.
 

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Go with a company that actually TESTS the projectors against Moire pattern. An example Stewart Filmscreen. They will test your screen, at specific sizes on any projector you tell them you will be using. I switched out my projector this year and had them verify that it was not going to be an issue. I did end up having to purchase a new screen, but with 1080p projectors out there, it was about time I upgraded anyways.
 
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