my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Operations   » Digital Cinema Forum   » NEC 2000C Moire Pattern - Possible Causes? (Page 1)

This topic comprises 2 pages: 1  2

Author Topic: NEC 2000C Moire Pattern - Possible Causes? Jim Cassedy Phenomenal Film Handler Posts: 1661 From: San Francisco, CA Registered: Dec 2006 posted 01-04-2015 04:22 PM                     I'm doing a preview later tonight at one of the screening rooms where I sometimes work. "The other guy" just informed me that the bulb on their NEC 2000C projector was recently changed, by a professional service tech and that ever since then, hs's noticed a slight moire pattern on screen that he's never seen before. (And I've worked there many times and if the moire was there previously, I know I would have seen it.) The otherprojectionguy sez that nothing else was changed or adjusted (other than the normal bulb-change-alignment) when the new bulb went in. I said I'd go down early & takalook, but quite frankly, I'm not sure exactly what I'm looking for. Does anybody have any ideas? It's an NEC 2000C- - and I beleive they have a 2K bulb inside, since it's only a screening room with a screen around 12-15ft wide, if I recall. He sez he's seen it on both flat and scope. The projectorthingy is equipped with Dolby 3D, which hasn't been used since the bulb change. (and the wheel should be well outta the light path & probably OK) I'm heading down there shortly, so if anybody has any ideas, please chime in! THANKS! -Jim C-  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 01-04-2015 07:55 PM                     The moire pattern is generated when the pixels and grid of the DMD's in the projector are at or near the same pitch of the screen perfs. Some times this can be minimized by getting the projector perfectly level with the perfs and or making the image slightly larger or smaller if any of this is possible and some times it can't be gotten rid of without changing the screen. Newer screens from Harkness and Severtson take this into account with modified perfs and there is less a chance of the moire. Mark  |  IP: Logged Jim Cassedy Phenomenal Film Handler Posts: 1661 From: San Francisco, CA Registered: Dec 2006 posted 01-05-2015 12:33 AM                     So, Mark- There's never been a moire pattern at this location before. I did notice that the projector has been moved very slightly from its' previous position, and that might have been enough to cause the moire to appear, from what you are telling me. I didn't see your message till I got home, but in the course of checking things, I did move the lens focus & zoom slightly and that seemed to clear up 98% of the moire. When I first got there, you could see it all over the screen, especially if you put up a peak or 50% white field. After 'fiddling' with the lens settings a bit the moire is now confined to one small spot in the lower left hand corner on a 'white screen' and it's totally invisible during actual content. I'll go back later this week when I have time & play with the projector position & check the level, but my time was limited today. As I mentioned to you once before, I still really want to go to the "NEC Projector School" for some advanced operator training or something like that. Barco & Christie Tech's are a dime-a-dozen here in SF, but NEC techs, not so much so. And I regularly deal with over half-a-dozen NEC's, so it would be worth my time. I don't care what the school costs- - that's not a problem. I'm still trying to find a hole in my schedule big enough for me to attend, and I'm still unsure exactly how to get into one. Thanks for the moire advice  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 01-05-2015 01:50 AM                     The moire pattern/zebra stripe issue is present across all brands of DCI projector manufacturers. I guess it would help if screen manufacturers would create a slightly "random" perforation pattern for new screens.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 01-05-2015 07:16 AM                     It may be that the moire has not been noticed before. Maybe someone carefully adjusted focus so that is was just not visible. And maybe this focus was now touched, even if they claim it wasn't. I guess it is also possible to shift a bit of focus with the bulb alignment. So, I would check the pattern, and if it is indeed visible, readjust the focus slightly for all formats to get rid of it again. - Carsten  |  IP: Logged Jim Cassedy Phenomenal Film Handler Posts: 1661 From: San Francisco, CA Registered: Dec 2006 posted 01-05-2015 10:39 AM                     quote: Carsten Kurz It may be that the moire has not been noticed before. Oh ho ho ho! Not very likely. Not only would I have noticed it on one of the many occasions I've worked that room, but one day last summer I spent 18hrs in that room working with a group of optical engineers who were contracted by a consortium of several of the large theater chains to evaluate different types of 3D glasses provided by several manufacturers. The day before the test a complete alignment& re-bulbing of the projector was done. On the day of the test they hauled in two huge road cases of scientific equipment, and spent the first several hours just calibrating everything. They also had two of those incredibly expensive (around $12,000 us)screen meter-things that they used to establish 'basline' data for their tests, and also to take readings every two hours to certify that the light levels were not 'drifting' any during the course of the day which would have affected their test results if they didn't factor those corrections (if any) into the data they were collecting. 95% of the work they were doing involved 'shooting white light' on the screen. Believe me- - if there had been a moire or ANYTHING wrong with the system that day, they would have stopped everything. I had to sign a non-disclosure agreement, so I couldn't take any pictures and exactly what they were doing and who they were specifically doing it for is still proprietary information. It will eventually be released in some form, and they promised they'd let me know when that happens. A professional photographer took a sh_tload of photos of the set up that day, as part documenting the way they collected the data. I hope I can share those once the info is published. (It was a long, but easy day for me. - I got paid a wholebuncha money to basically just stay out of their way all day. Nice!)  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 01-05-2015 11:38 AM                     That said...I can GUARANTEE that there was Moire. There is no way around it with a fixed grid screen and fixed grid projector. All you can do is minimize it. Zooming the lens can often push the grids so they are less objectionable. This is one of those scientific facts you just can't dance around...two superimposed grids (regular grids)...will Moire. What you are left with is how apparent it will be based on how the two grids "beat" off each other.  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 01-05-2015 12:29 PM                     Um. Maybe you should rephrase that, Steve.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 01-05-2015 01:00 PM                     Jim, Forget about the lamp. Put a white pattern on screen, de-focus the picture and I bet the moire will disappear.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 01-05-2015 01:07 PM                     I agree that it's always been there to some extent. It is a fact of DLPee projection. The fact that your projector was moved from it's normal position may have exacerbated it. Throw up the alignment test pattern and be sure the projector is where it belongs on screen. Once you verify that then tweak zoom and focus slightly to minimize it. Mark  |  IP: Logged Jarod Reddig Jedi Master Film Handler Posts: 513 From: Hays, Ks Registered: Jun 2011 posted 01-05-2015 01:34 PM                     It is indeed common knowledge that morie is the interaction between the screen perf pattern and the DMD grid. One way to get around it is to have the screen cut at an angle at the factory if its an option. Or as you posted adjust fine focus to minimize.  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 01-05-2015 04:59 PM                     I still don't get why the likes of Harkness, who now push out almost exclusively "digitally optimized" screens aren't able to deliver "randomized" perforations. This would get rid of the problem for once and for all. Is it because it would affect the tension strength of the screen rather negatively or am I missing something else? quote: Jim Cassedy Believe me- - if there had been a moire or ANYTHING wrong with the system that day, they would have stopped everything. On the other hand, even if there was some slight moire, it shouldn't really have affected their measurements.  |  IP: Logged Jarod Reddig Jedi Master Film Handler Posts: 513 From: Hays, Ks Registered: Jun 2011 posted 01-06-2015 12:04 AM                     It probably has to do with how sound would interact with a non-uniformed perf pattern but its just a guess.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 01-06-2015 05:59 AM                     At best it would be a semi-random pattern. The way most screens are made by seaming it together, one has to be careful about having the pattern not mate up well when seamed. Then there is the problem of an irregular yet periodic pattern is actually more visible than a regular one. Your eye isn't going to fixate on constant/uniform...but it WILL notice something that is different. Stewart Filmscreen effectively has an irregular pattern and they don't normally show Moire very much (must less than other screens). However they get their random perforations due to human error. Their screens are seamless and the perforations are applied after manufacture...as a result they tend to weave a bit. However, sometimes they weave into each other and you get some overlapping perfs. This can be every bit as visible as a seam. Again, your eye will pick off differences more than the same. Note, Stewart also rotates their perf pattern to not be on the same grid as a digital projector to even further minimize Moire. Overall, I still like Stewart the best but they just aren't worth the 4-5 times the expense in a typical movie theatre...in a screening room, they can sure make a movie "pop" like no other screen I've seen.  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 01-06-2015 04:59 PM                     I've always asked myself how they get the perforations in there. I imagine it like them using something like big rollers with the perforation patterns on them. In this case, it will be impossible to create a truly random pattern with this technique. You definitely want to avoid something like a wallpaper pattern occurring, but even if the perforations are semi-random and the repetitive pattern is sufficiently spaced out (like only occurring like two times on a certain screen) it should still work I guess? Because I doubt the average brain would be able to correlate this data into something of a repetitive pattern.  |  IP: Logged

All times are Central (GMT -6:00)

This topic comprises 2 pages: 1  2

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.