1. The version I saw they played 2 films at the same time while I had to watch the feature with grey tinted glasses. What does playing 2 different films at the same time do?

2. Do you thread both films in the same projector or how do you thread for this sort of thing?

3. What do the glasses do?

4. Why did some of the movie not seem all 3-D?

5. On IMAX or OMNI, why is the film fed through sideways instead of being fed vertically?

6. On the projector, is the thread path similar to a projector that plays top to bottom? Does it even have loops?

7. Does anyone have any pics of an IMAX projector head?

8. Is the projector head gearless or does it use gears with belts or what is the setup?

9. What is the term "Polarized" mean?

10. Can you use Film-Guard on the prints?

Well I think that is all I will bug with for now. Appreciate it. Thanks!

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--"That's my story and i'm sticking to it!"--

2: not sure for all projection systems, but the SR system has twin projectors.

3: The glasses contain two polarising filters the left eye filter is rotated 90 degrees from the right eye. Similar filters are placed in front of the projection len's. The projected image for each eye is polarised in a differernt direction. Because the polarisation of the right print is 90 degrees out of phase with the filter on the left eye glass none of this image can get through, the same with the right eye the polorisers ensure the right eye can't see the left print.

4: Depending on the composition of the shots depends on how 3 Dimensional they look.

5: Film goes through sides ways to maximise negative area. 70mm was chosen because it was readily avalible, the frame area for an Imax print is about 3 times larger than normal 5 perf 70mm.

9: Polarised is a term applied to light - a normal light wave vibrates up and down and left and right, in all directions around a central point. A Polarsing filter restricts the motion of a light wave to one plane only, under a microscope a polarising filter looks like a comb - this restricts the motion of the light hitting it to only up and down. Two of these combs at 90 degrees to each other will cancel out all of the light.

10: no - many prints are photoguarded though.

Hope this helps

Phil

I always say...when you learn IMAX, you take the very basics you know about projection, then you throw the rest out the window because you won't be needing it.

It creates its own loops called the rolling loop system. It has no intermittant movement but relies on the movement of the rotor and sprocket to create the loop to allow the print and frame to stop for projection.

>>7. Does anyone have any pics of an IMAX projector head?<<

That's a tricky one. Here at least, they're pretty funny about releasing that sort of info in picture form. If you ask though, you would probably be allowed access to the booth to take a look. (Mention Film-Tech and receive 10% off!)

>>8. Is the projector head gearless or does it use gears with belts or what is the setup?<<

Belts.

We don't run the SR system (2 machines) in Sydney...Both our prints (Left and Right) run through the same machine one above the other and an offset of about 5 sprockets. (Left first, right second). On an SR setup, each version runs through a separate machine.

Next time you go, ask to see the booth...you never know...

 

I'll try and answer some of your questions.

1) the two films are for the left and right eyes.Your perception of 3D in the realworld relies on you seeing two separate images slightly separated.In "conventional" 3D films the lenses of the two cameras are positioned to mimic the position of your eyes.The distance between the lenses is known as the interoccular measurement.

2)Dependent on which theatre you were at the films may have been threaded through one or two projectors.Most IMAX 3D theatres use what are known as the twin rotor GT systems.In these the two films run through the same projector one above the other. The other option is having two projectors where one film runs through each. This can either be an older "classic" sytem or the newer SR system which is what we have here in Bradford. Photographs of this type of system are in the Pictures section of this site under Cinemark Tulsa.

3) if you projected the two films onto the screen and viewed them without glasses you would get a ghosted or laterally diplaced image.

In order for you to get the 3D effect you left eye must see only the film from the left projector and similarly right from the right.

To enable this to happen the separate images are projected and viewed through linear polarisers at 90 degrees to each other.

The viewing polarisers are the "grey tinted " lenses in the glasses.
This effectively stops the left eye seeing the right image and vice versa. For description of linear polarisation see http://www.polaroid.com/products/oem/polarizers/pola-types.html

4) Sideways not horizontally?

5) Description of Imax projectors taken from Jim Neihouse's site http://www.1570films.com/

IMAX projectors are the most advanced,highest-precision and most
powerful projectors ever built. The key to their superior performance and
reliability is the unique "Rolling Loop" film movement. The Rolling Loop,
originally invented by Ron Jones, an Australian, adapted and enhanced
by Imax, advances the film horizontally through the projector in a
smooth, wavelike motion. During projection, each frame is positioned on
fixed registration pins, and the film is held firmly against the rear element
of the lens by a vacuum. As a result, the picture and focus steadiness
are far above normal standards. The 68 per cent shutter transmits
one-third more light than does the 50 per cent shutter in conventional
projectors.

The popular success of Imax's 3D systems, IMAX® 3D and IMAX® 3D
Dome, led to the development of IMAX® HD, which is shot and projected
at 48 frames-per-second, twice the normal motion picture standard
frame rate, providing even greater depth of field, clarity of detail and
steadiness to the already spectacular IMAX image.

In 1997, Imax introduced a 3D projection system (IMAX 3D SR)
designed for smaller markets which can be integrated into an existing
multiplex theater system.

This site also shows frame comparisons etc

IMAX projectors do not have intermitent sprockets or claws.
As for using Film Guard - who knows?
 

The "rolling loop" concept used in IMAX projectors is an Australian invention. See the paper "The Rolling Loop -- A New Concept of Film Transport", by P.R.W. Jones in the January 1968 SMPTE Journal.

The "birth" of the IMAX system is chonicled in two papers by William C. Shaw:
"Film Dynamics of a Rolling-Loop Film-Transport System" and "New Large-Screen and Multi-Image Motion-Picture System" both published in the September 1970 SMPTE Journal.

I first saw an IMAX film in 1971, at the Cinesphere at Ontario Place in Toronto (home of Gordon McLeod), where IMAX Projector #1 still resides. The film was "North of Superior": http://www.imax.com/films/distribution/north_of_superior.html

I've been an IMAX film fan ever since, and take every opportunity to visit theatres and see different films.

The IMAX DOME 3D ("SOLIDO") film "Echos of the Sun" was a very unique experience, as it is a 3D IMAX film projected on a dome screen. It was a mind-blowing experience for its sense of reality, as the 3D image surrounds you!: http://www.imax.com/films/distribution/echoes_of_sun.html

Kodak worked very closely with IMAX and IMAX theatres to optimize the performance of our 70 mm VISION Color Print film in their projectors.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

1570 is just polyester film, it's just a little bigger. The catch is, that if the print has been Photoguarded you wouldn't want to try and applying Film-Guard. They don't mix well. Most of the prints I get, and plan on keeping for a full run are brand new, it would just be a matter of asking that the print not be Photoguarded. Although it's not really necessary, I have a print of 'Mysteries of Egypt' that we have shown every day, several times a day for over a year and it's not dirty. It has some wear marks, but it is not dirty in the slightest.

I don't know of anycompany that makes a dry media type cleaner for a 1570 projector. So you couldn't apply Film-Guard in the most effective way.

I don't know about the IMAX projectors, but mine have two types of cleaners on them. They have 4 PTR's (two before the head, and two after) as well as what call the 'vaccuum cleaner.' It's a series of horsehair bristled rollers in a closed shell that has a vaccuum attatched to it to remove any dirt. I didn't describe it well, but it works pretty good.

A lot of people have ambliopia and get 3-D visual cues from focus, or by shifting head positions. For them, any 2-D movie looks 3-D.
 

*The print can not have 3M Photoguard coating on it.

*A standard 70mm Kelmar cleaner would work fine for application, but due to the flat field lens with it's suction, the cleaner would have to be placed on the "take-up" end of the film path using a custom designed mount. I would recommend if anyone ever decides to try this do so on an old print that is going to be tossed. Soak down the pads and wait 24 hours (so any oversaturation of the pads would evaporate to a low level) and run it on the last show of the day. This should end up with a very, very light coating of FG on the print which I wouldn't imagine would cause a problem with the suction around the lens. As far as compatibility issues with the film stock itself, that's not a problem. The problem comes with the projector design. I'm not an IMAX operator, so since this is untested grounds, it would truly be a "do at your own risk" sort of thing.

With all of the flying dust I see on typical IMAX prints, it would seem to me that this would be worth testing. If anyone ever does, please let me know.

You'd end up with an unsightly mess up on the screen as the field lens cycled.

Even applying it on the out side, the print is moving so fast that it wouldn't dry too much before it was back in the roll.

AFAIK, the IMAX projection equipment is not owned by the theatre, it is leased. So IMAX has strict specifications regarding equipment maintenance and operational procedures. These definitely include things such as the cleanliness of the projection room, and the ambient conditions such as relative humidity. IMAX runs training programs to certify Chief Projectionists, and has a worldwide service program.

In almost all of the IMAX theatres I have visited, the projection room has been very clean, organized and well run. The projectionists take great pride in their work, and in developing their skills in handling this premier film format.
http://www.imax.com/innovations/theatre/index.html
http://www.1570.com/

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
 

The platters are either side of the projector for left and right versions...the print always runs through the machine the same way though...the left print just has to travel a little further on the way in.
 

You were in the Indianapolis IMAX 3-D, where Gary Weyers is the chief projectionist...by far the strictist and cleanest booth in the land...out of his own pocket he pays for the fly paper walk in pad that gets changed every day, as well as disposable booties for those that don't have their own "booth shoes."

He has PTR rollers on either side of the rotor (sticky going into the rotor, less sticky on the output side). The PTRs are all changed for EACH showing.

As to the "reel-units"...he has two MarkIIs with 60" decks, 4-decks per reel-unit. What you may not have noticed is the two roller trees between the projector and the reel units so the film may start on either reel unit and end up on either reel unit. For 3-D features, both "eyes'" films are going in the same direction though logistically they may not start nor end up on the same reel unit. As you face the screen, both strips of film feed from the right. The whole system is in triangular formation.

As to Film-Guard on IMAX...I wouldn't do it...it will for sure slime up the field flattener. We have supplied the Inidanpolis IMAX-3D with Film-Guard for their conventional 35/70 system. Incidentally, they use 7000 watts on 35mm with no problems. But don't try this at home! ;-)

Steve

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"Old projectionists never die, they just changeover!"
 

Gary's booth never seems to age...he keeps it spotless!

Steve

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"Old projectionists never die, they just changeover!"
 

I hadn't thought about the field flattner when considering my first post. It would definately cause all kinds of problems there no matter where the cleaner was mounted, or how smooth the Film Guard was on the print.

Like Gordon, I also have very little trouble with dirt. One or two Field flattner changes per show is all that is ever needed on a regularly run print. New prints are a little dirtier, but after a few days have no problems.

BTW, Gordon, what do you use on your Field Flattners up in Canada? I use a product called Dry Wash 'N Guard, that was reccomended by the projector manufacturer.

Question:
Why would Film Guard casue the projector to jam? My print of "Mark Twain's America" has been photoguarded and is VERY slick. I have to be extremly careful with it so as to not cinch it with a slight spin of the platter it's so slick. When it first arrived it was so bad that I had to clean the platter every show, there was actually a slight build up on the platter from the print sitting on it for just a matter of 1 or 2 hours. What would be so different about Film-Guard that would cause a jam if the print was slick?
 

Putting a thin film of oil or other material between two very smooth surfaces (the field lens and the film) acts like a "glue" on a molecular basis, and would cause them to stick together. So trying to change/clean the field flattener while the treated film is running could jerk the film out of position, causing a jam.

To illustrate, take two plates of glass and put a drop of oil between them. When the oil spreads out, it will cause the glass plates to stick to each other, not slip.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
 

Thanx for the illustration JP
 

For sound they had 35mm mag film running in conjunction with a digital version on a disc, somewhat similar to DTS, but without the timecode. The sound is synchronised with the picture through the automation system. The film needs to be threaded in an exact spot and then the sound and picture start at the same time (has anyone seen Singing in the Rain?).

If the film breaks, the same piece of Mag sound must be removed and the disc be edited through the Automation.

Similarly, if one of the 3D prints has film removed, it must either be replaced with black spacer or the same amount removed from the other print, otherwise the two prints end up out of sync with each other and the 3d effect can be lost.

I was interested to hear that there is no racking control on the projector, and due to the sound no being part of the film, if you start up out of frame, you loose the session, as there is no way to change the framing, and by stopping the projector to fix it you loose your sound link.

In case anyone is wondering, the film is moving too fast to support a time code track.
 

quote:

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Ethan, if you weren't seeing the film in 3-D, there could be two causes. The LCD shutters on your headpiece might not have been working properly, or you could have ambliopia,(sp?) sometimes called lazy eye.

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Also a cause can be strabismus (cross-eyedness). Amblyopia & strabismus can & usually are caught in routine eye exams. Or...it may turn out that you're just not "wired" for stereo. Those neural pathways are developed in infancy & early childhood. If they don't, it's one eye: flat; two eyes: scope. Or the favorite of focusing near & far simultaneously for max depth of field. Or "alternating use": stereoblind folk rarely have the "tired eyes" feeling.

A stereo vision test is often not the usual part of an eye exam, but if you go to one of the monolithic chain vision centers (Opti-World, etc), they have monolithic standardized tests to check for EVERYTHING (like the military). So don't be shocked if Opti-World checks both your stereo vision & prostate.

quote:

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A lot of people have amblyopia and get 3-D visual cues from focus, or by shifting head positions. For them, any 2-D movie looks 3-D.

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Those are "monocular depth cues", & included are relative size & changes in relative position in the field of vision. I am stereoblind, & did not know until I was 35 & idly took a stereo vision exam to kill some time! Monocular depth cues are so successful that I apparently used them to pass those old "miniature in the box" 3D exams for driver licenses. And used them for SCCA rallying & who knows what else for 35 years.

For the stereoblind 2D movies still look like flat 2D & not at all like the spatial arrangement of the rest of the world, since fewer monocular cues will work on a 2D movie; & most importantly, the automatic mental processing of the interaction & differences in the monocular cues tosses the movie out as non-real when the results are aberrant. Apparent size cues OK but items apparently at different distances do not respond correctly to focus changes? Toss it out.

3D movies look like 2D movies, only dimmer.

The 3D effect "works" on the Stereo People only because it mimics their stereo cues of convergence. The Stereo People also use monocular cues, but it seems that in their perceptual development they've assigned such an outsize importance to convergence that those binocular cues are enough for the 3D Movie Experience.

Glad I found this out before I was ever asked to run a 3D movie!

"The people in the audience are screaming & throwing up! What's wrong with the movie?"

"Hmm, looks fine to me..."

It's estimated that *at least* 10% of the population is stereoblind, and that number could be *very* low because many who are stereoblind do not know it. So about 10% of the folks in each 3D movie are wasting their money! Everybody should get checked for stereoblindness, though. Especially kids: they check them for colorblindness, they oughta check them for stereoblindness before sending them out to get beaned by baseballs!

Is this right? or does this only apply for the Polaroid glasses?
 

The liquid crystal glasses (PSE headsets) switch each eye off and on in sync with the projector shutters, and tilting the head does not cause fringing.
 

If you twist your head with the LCD shutter glasses, the offset images won't be where your brain thinks they should be. It doesn't make your brain a happy camper.

 

Can you tell me more about the automation at IMAX and how it works? How similar is it to a standard cinemas automation system?

Also, do all IMAX theatres run advertising off a 35 mm machine. The one in Melbourne does (Vic 8 35/70). The ads only fill about 30% of the screen and look very bad!!!

Finally, does anyone know what the magnification is for an IMAX setup. I know that this depends on the situation, but does anyone know what the average magnification is?

Frank.
 

quote:

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Titling the head with the polaroid glasses can allow the images to reach the wrong eye, visible as seeing both images fringing.

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Wouldn't you stereo people tend to keep your head pointed the correct way, though? It seems the feedback of "3D better, now worse, etc." while the head moves around would be similar to the way auditory feedback causes you to point your head toward a sound source.

Of course feedback would cause someone at a 3D movie to orient his/her head to optimize the 3D.

So, in all those pictures you've seen of people in theaters wearing those 3D glasses staring straight ahead like the Devo army: haven't you noticed that here & there are people whose heads *aren't* in that perfect alignment, looking like out-of-step dancers in a chorus line?

Those are the stereoblind people.

Assuming a typical Imax screen is 25 meters across (78 feet-ish) and the frame area is approx 69mm across - the magnification required to fill the screen is 362 times.

In comparison on a screen 10 meters (33 feet ish)wide a 20mm frame of 35mm film needs to be magnified 485 times. Trying to fill a 25 meter imax screen in the horizontal axis would require a 35mm frame to be magnified approx 1250 times.

Assuming I've got my maths right, otherwise feel free to ignore me.

You can see pictures of the IMAX SR booth setup in the picture warehouse under Cinemark IMAX Tulsa. If Providence is a 2-projector booth, it should have the same setup (although probably more walking room!)

The projectionist in Providence RI is Jim Didio, who transferred from the Syracuse NY Museum of Science and Technology IMAX dome theatre. He is active on the 1570 User Group.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
 

Evans