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Author Topic: Dunkirk - 15/70 Imax version Chris Haller Film Handler Posts: 68 From: Rochester, NY, USA Registered: Dec 2015 posted 08-03-2017 01:23 PM                     Bobby - IMAX projectors have a mechanism that actually actively cleans dirt off of the projection lenses on a regular basis during the show. I don't remember the specifics, but it's kind of like a windshield wiper of sorts. Sometimes it cleans the specs of dirt or hair that are in the gate or on the lens, and sometimes it just moves in around. I saw the 15/70mm print of The Dark Knight Rises off of an IMAX SR projector in Rochester 4 times, and on the last screening, which was literally the last showing of the print they ever showed, there was like a decent chunk of debris on the lens right in the center of the image. Whatever it was was significant enough that the wiper couldn't remove it at all, and just sort of spread it over the 6-story tall image on the screen for 2.5 hours. It's not a particularly tough wiper, and moves fast enough that you can't really see it, but it certainly has its flaws. At least the dirt you saw wasn't too damaging to the presentation!  |  IP: Logged Victor Liorentas Jedi Master Film Handler Posts: 800 From: london ontario canada Registered: May 2009 posted 08-03-2017 02:31 PM                     I believe some or all projectors have a air blower as well. If the projectionist is monitoring the show as they are supposed to do,they can decide when to hit it. I could be mistaken.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 08-03-2017 04:37 PM                     quote: Chris Haller I don't remember the specifics, but it's kind of like a windshield wiper of sorts. Sometimes it cleans the specs of dirt or hair that are in the gate or on the lens, and sometimes it just moves in around. Can someone confirm this? I find it hard to believe someone actually installs a mechanism that is constantly moving dirt over a lens surface, ruining at least the lens coating within a few days. Why would it need more than a wind blower to clean off some dust. What kind of debris can build up on an IMAX projection lens that wouldn't also build up on any other projection lens? I could imagine they have some sort of cleaning system for the port windows, that is operated before the show, yes. But constant lens cleaning? - Carsten  |  IP: Logged Paul Mayer Oh get out of it Melvin, before it pulls you under! Posts: 3836 From: Albuquerque, NM Registered: Feb 2000 posted 08-03-2017 05:55 PM                        Imax projectors use a sold piece of quartz glass called a field flattener located in the gate. The rolling loop mechanism rolls each film frame onto the field flattener and its registration pins to hold the film in precise alignment. The rotor that forms the rolling loops also incorporates the shutter which gives two flashes per frame. The rolling loop then lifts/rolls the film off of the field flattener/registration pins, and rolls the next frame into position in the gate. Air is used both to help form the film loops and ensure that the film is held firmly in place on the field flattener quartz. The quartz is designed to be a bit taller that twice the width of the film, and mounted into a rail assembly that allows the the flattener to move up and down against some wiper bars and air jets so as to provide a freshly wiped quartz area for the film to be rolled on to and off of every few seconds (the interval can be set by the operator). The quartz is cleaned between every show and sometimes a fluid such as RainX is buffed into the quartz as well to help prevent bits of dirt from sticking to the quartz. Sometimes the dirt does indeed stick - that's why you'll occasionally see some stationary specks of dirt somewhere in the frame, then they disappear, then they return to the same place every few seconds or so, depending on the wipe interval set by the operator. The wiping can also be set to manual control. The operator has a handheld remote control with a button to manually move the quartz across the wiper bars, and a rocker switch to make small changes in lens focus.  |  IP: Logged Chris Haller Film Handler Posts: 68 From: Rochester, NY, USA Registered: Dec 2015 posted 08-03-2017 07:28 PM                     I knew there was a mechanism like that, but I'm glad someone with more technical expertise stepped in to cover my knowledge gap - thanks Paul, I appreciate the explanation. Having never actually operated an IMAX projector or well.....any projector in general, my secondhand knowledge is often questionable at best.....  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 08-03-2017 08:23 PM                     Wow, a google search for IMAX field flattener shows many hits in this forum regarding this topic. Seems the reason for this cyclic wiping mechanism is that each IMAX film frame get's in direct contact with the field flattener glass during the stop phase, instead of just moving in front of it. So, naturally, any dirt on the film has a chance to get stuck on the glass. Whereas in 'normal' projectors, that dirt is simply carried away with the film when it transports, as it touches nothing in the gate. - Carsten  |  IP: Logged Jonathan Goeldner Phenomenal Film Handler Posts: 1360 From: Washington, District of Columbia Registered: Jun 2008 posted 08-04-2017 06:06 PM                     so what's the deal with the IMAX-laser version is it indeed 12-channel ?? - the Smithsonian claims it is, and from what I heard there seemed to be movement of surround sound cues on the side walls and to the rear corners. The soundmix in generally was so deafening, sound delineation at times obscured any attempts to be truly holospheric - the barrage of music and sound effects was relentless. I know imdb is never 100% correct when it comes to tech specs, but having all there immersive audio mixes: DTS-X, Dolby Atmos, and 12-channel IMAX laser sound all listed at one point, guess which one they edited off the list, yes the one that supposedly is the correct one (the latter). I thought Nolan only exclusively mixed in 5.1 and at a volume amplified setting of '11'  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 08-04-2017 08:20 PM                     IMAX laser does have 12 sound, but wether Dunkirk makes use of it, I don't know. If there is no time/licence to do a real 12ch mix, maybe IMAX mastering is allowed to do some 'creative upmixing'. You are right, if an IMAX laser movie plays ridiculously loud, it may become impossible to discern the additional channels. - Carsten  |  IP: Logged Chris Haller Film Handler Posts: 68 From: Rochester, NY, USA Registered: Dec 2015 posted 08-07-2017 09:24 PM                     CINEMA: Maryland Science Center AUDITORIUM: St. John Properties IMAX Theater SEATS: Didn't catch the row/number - smack dab in the middle though PRESENTATION: Film presented without trailers on 15/70mm IMAX film I'm back on the east coast on a week excursion to Maryland with family. It rained like cats and dogs, so we all drove into Baltimore to see Dunkirk on the science center's IMAX screen. I knew from youtube videos and various readings that this IMAX utilized a 3D GT style 15/70 projector and "38 channels of surround sound." I had family who hadn't seen the movie yet, so I figured this was a great excuse to see a classic science center IMAX presentation. Honestly, for all 12,000 watts of light that the GT projector's bulb is supposed to output, the 15/70mm image was disappointingly dim compared to how I saw the film in Los Angeles at CityWalk. The screen was larger than the screen at CityWalk, but that projector just did not seem capable of lighting that entire screen properly. I got the idea from the projectionists that I spoke with after the show that they way not be running them at full intensity - they talked a bit about how they were trying not to play 3D movies to make their bulbs last as much as possible. I also noticed the same kind of image shaking that I saw in LA here in Maryland. Like, identical subtle movements. The 5/65 footage looked nearly identical with damage, contrast, and color issues included. The material they used to make the 15/65 printing negative definitely was not prepared with the utmost quality control. Someone slipped up at Fotokem or something, because there was some pretty noticeable speckling. Oh well. As I mentioned, I did get to speak with the projectionists after the show, and I did get to see the booth after speaking with security. It seemed like a pretty well maintained booth, with nice climate control and whatnot. They didn't have a fancy vault of IMAX science films, but rather a couple of wooden shelves on which they kept their IMAX movies. There were two people operating the GT in the booth - the woman threading the next Dunkirk show was totally into talking about the process and how they ran their shows, but the older man in the booth was totally not into answering questions and whatnot. Oh well.  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 08-07-2017 11:05 PM                     quote: Chris Haller Someone slipped up at Fotokem or something, because there was some pretty noticeable speckling. Chris, was the speckling you saw clear by chance? If you are just talking about little black spots that were on screen for one frame at a time, that's just a dirty print. If the little black spots hung around for a second (or several), that's just dirt on the field flattener, again a dirty print. I'm curious for clarification, as I doubt with the few IMAX prints struck that Fotokem actually let the printing negative get dirty.  |  IP: Logged Chris Haller Film Handler Posts: 68 From: Rochester, NY, USA Registered: Dec 2015 posted 08-08-2017 06:19 AM                     quote: Brad Miller Chris, was the speckling you saw clear by chance? It was primarily black and white speckling in the 2.20:1 image and not in the black of the letterboxing, only in the 5/65mm sequences of the movie. Aside from field flattener debris having to be cleared by the IMAX's wiper mechanism, the 15/65mm footage was clean as a whistle. Same deal with the 15/65mm footage in LA as well. I know it sounds crazy, but I find it unlikely that these projectors are only damaging non-IMAX sequences in Dunkirk. Everything would have to fall into place just the wrong way in both of these settings in the same way for these prints to look so similar. I'm no expert though.....  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 08-08-2017 12:14 PM                     Ah I understand now. I misread.  |  IP: Logged Bill Brandenstein Master Film Handler Posts: 413 From: Santa Clarita, CA Registered: Jul 2013 posted 08-08-2017 06:43 PM                     I remember seeing a little speckling in the 5/65 blowup parts at CitiWalk. Perhaps it should've been zero in this day and age, but I didn't think it was all that much, and while in that respect it brings the presentation down a notch from perfection, I didn't think it was intrusive. Ought to go back before it's gone. It's still at the Cinerama Dome too.  |  IP: Logged Tyler Purcell Expert Film Handler Posts: 180 From: Van Nuys, CA Registered: Dec 2015 posted 08-09-2017 02:33 AM                        The speckling was only part of the issue. The grain structure, color and contrast were also nowhere near matching the 15/65 material. That's what upset me more then anything else, there was no reason for it. The trailers before the movie looked better then the 5/65 material.  |  IP: Logged Bill Brandenstein Master Film Handler Posts: 413 From: Santa Clarita, CA Registered: Jul 2013 posted 08-09-2017 09:41 AM                     No argument there. The trailers weren't sharp, but they otherwise looked very good, meaning that a digital out made for a more pleasing gamma/grain/saturation look than a completely film process. Did you notice the final 5/65 shots set in the train at the end, lit by sunlight? They looked really clean. Makes me wonder if the rest were underexposed.  |  IP: Logged

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