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» Film-Tech Forum   » Operations   » Large Format Forum   » Questions on 3-D Imax (Page 1)

 
This topic comprises 3 pages: 1  2  3 
 
Author Topic: Questions on 3-D Imax
Ethan Harper
E-dawggg!!!

Posts: 325
From: Plano, TX, USA
Registered: May 2000


 - posted 11-08-2000 11:25 PM      Profile for Ethan Harper   Email Ethan Harper   Send New Private Message       Edit/Delete Post 
I recently was watching "Cyberworld" in 3-D at the local IMAX. It didn't really seem 3-D to me, although there were a couple scenes in the feature that did appear 3-D. Any ways it got me thinking so I have got some questions about 3-D.

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!

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


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Phil Connolly
Film Handler

Posts: 80
From: Derby, England
Registered: May 2000


 - posted 11-09-2000 03:19 AM      Profile for Phil Connolly   Author's Homepage   Email Phil Connolly   Send New Private Message       Edit/Delete Post 
1: You have two prints, one for the left eye and the other for the right eye. The glasses ensure the right eye only sees the right print and the left eye only sees the left print.

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


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John Wilson
Film God

Posts: 5431
From: Sydney, Australia.
Registered: Dec 1999


 - posted 11-09-2000 03:48 AM      Profile for John Wilson   Email John Wilson   Send New Private Message       Edit/Delete Post 
>>6. On the projector, is the thread path similar to a projector that plays top to bottom? Does it even have loops?<<

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...

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Dick Vaughan
Phenomenal Film Handler

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From: Bradford, West Yorkshire, UK
Registered: Jul 2000


 - posted 11-09-2000 04:58 AM      Profile for Dick Vaughan   Author's Homepage   Email Dick Vaughan   Send New Private Message       Edit/Delete Post 
Ethan

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?

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John Pytlak
Film God

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From: Rochester, NY 14650-1922
Registered: Jan 2000


 - posted 11-09-2000 06:50 AM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
Here are some links to additional information on 15-perf 70 mm projection systems:
http://www.imax.com/index.shtml
http://www.1570.com/
http://www.lfca.org/
http://www.giantscreentheater.com/4.htm
http://istcon.org/bigframe/index.html
http://www.cinergetics.com/
http://www.1570films.com/
http://www.cfi-hollywood.com/process.html

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.

------------------
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


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Dave Cutler
Master Film Handler

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From: Centennial, CO
Registered: Jun 2000


 - posted 11-09-2000 09:03 AM      Profile for Dave Cutler   Email Dave Cutler   Send New Private Message       Edit/Delete Post 
Seems everyone already answered all your questions well, except the last one about Film-Guard.

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.


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Jerry Chase
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From: Margate, FL, USA
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 - posted 11-09-2000 10:09 AM      Profile for Jerry Chase   Author's Homepage     Send New Private Message       Edit/Delete Post 
Eathan, 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.

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.

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Scott Norwood
Film God

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From: Boston, MA. USA (1774.21 miles northeast of Dallas)
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 - posted 11-09-2000 11:17 AM      Profile for Scott Norwood   Author's Homepage   Email Scott Norwood   Send New Private Message       Edit/Delete Post 


Aren't most IMAX prints photoguarded, anyway? If so, Brad says that FG won't do any good, since it doesn't adhere to the coating (or something like that).

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John Pytlak
Film God

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From: Rochester, NY 14650-1922
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 - posted 11-09-2000 11:47 AM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
Scott:

AFAIK, most new prints are NOT treated with Photogard (3M Scotchgard Film Protector). These UV-cured coatings are usually only used to "rejuvenate" used prints with back-side scratches. A few companies like FilmMack do routinely use it on new prints.

I would not recommend FilmGuard be used on IMAX prints, primarily because of the unique design of the projector, which puts the film into intimate contact with the hot quartz "field lens".

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Brad Miller
Administrator

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From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99


 - posted 11-09-2000 01:50 PM      Profile for Brad Miller   Author's Homepage   Email Brad Miller       Edit/Delete Post 
I've never had the opportunity to try FG on an IMAX print, but basically it all boils down to:

*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.


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John Wilson
Film God

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From: Sydney, Australia.
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 - posted 11-09-2000 02:00 PM      Profile for John Wilson   Email John Wilson   Send New Private Message       Edit/Delete Post 
I really think Mr. Pytlak is right about the field lens...

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.


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Brad Miller
Administrator

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From: Plano, TX (36.2 miles NW of Rockwall)
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 - posted 11-09-2000 02:40 PM      Profile for Brad Miller   Author's Homepage   Email Brad Miller       Edit/Delete Post 
That's why the only way I could see it possibly working would be to install it on the take-up end of the chain, so the film could wrap against itself and smooth out the coating. Does anyone know just how much air suction there is on the lens?

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Dennis Atkinson
Expert Film Handler

Posts: 129
From: Birch Run Michigan
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 - posted 11-09-2000 04:31 PM      Profile for Dennis Atkinson   Author's Homepage   Email Dennis Atkinson   Send New Private Message       Edit/Delete Post 
If I remember right, the 3D Imax booth I was in had full platters on each side of the projector. So each film went through the gate in a diffrent direction. Are all Imax booths run like a "Clean Room"?

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John Pytlak
Film God

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From: Rochester, NY 14650-1922
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 - posted 11-10-2000 07:24 AM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
Dennis:

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/

------------------
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

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Scott Norwood
Film God

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From: Boston, MA. USA (1774.21 miles northeast of Dallas)
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 - posted 11-10-2000 08:28 AM      Profile for Scott Norwood   Author's Homepage   Email Scott Norwood   Send New Private Message       Edit/Delete Post 
I once met an IMAX projectionist who was very knowledgeable about the format, but had not run 35mm before. He knew all sorts of things about rolling loops, mag dubbers, and such, but was (understandably) totally unfamiliar with changeovers, optical sound, and the different combinations of lenses and aperture plates (Academy, 1.66, flat, scope, etc.) that are common knowledge for anyone who works with 35mm.

IMAX is a neat format; I've never seen a bad IMAX/OMNIMAX show. On the other hand, I also like 16mm, which can look very good under the "right" conditions.

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