Film-Tech Forum ARCHIVE: IMAX

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Topic: IMAX

Joe Redifer
You need a beating today

Posts: 12859
From: Denver, Colorado
Registered: May 99

posted 07-26-1999 06:04 PM

Has anyone ever seen a scrathed or dirty IMAX print? I have not. It simply does not happen. You would think with all of that constant rewinding that there would be some nasty effects over time, but there are none. The films are always sparkling clean as well. Do IMAX operators simply put us to shame? What's the deal? And why do IMAX movies always suck! I want a good MOVIE in IMAX, not some national geographic special. I don't want something lame like Fantasia 2000 either.

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Keith Richardson
Film Handler

Posts: 11
From: Bartlett, New Hampshire USA
Registered: Jul 99

posted 07-26-1999 06:16 PM

is fantasia 2000 going to be IMAX? Because if it is, it is going to see a lot of running time because, as you said, IMAX lives on forever. I don't thinkit's the projectionists, it's the fact that it's made to last longer...it's for the "richer" companies.

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 07-26-1999 08:26 PM

The IMAX operators I know are TOP NOTCH! You will definitely never see a popcorn kid in an IMAX booth. There are also fairly extensive tests they must pass to qualify.

As to the format, remember it is considerably bigger than what most people on this forum are used to. A piece of dirt on a 35mm film which would be objectionable might not even project on an IMAX print, as there is less of a blowup. The equipment is also much better than your run of the mill movie theater's.

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Sheldon Harris
Film Handler

Posts: 16
From: Chicago, IL USA
Registered: Jun 99

posted 07-27-1999 10:52 AM

I have personally visited the "Regal" Imax booth here in Chicago. It is the first installation up and running by Regal. They consider it their proto type test installation and the place where they are learning and working out the bugs. I understand that Regal has committed to 10 Imax's up and running within the next couple of years. They are doing everything possible to run a first class operation here. The theater is magnificent. Unfortunately, they have run into a problem in controlling the humidity in the booth and have had to cancel some performances. Chicago can be very hot and humid in the summer. The Imax booth as originally installed has air conditioning/humidity problems which are being worked on. I saw the 3D "Encounter" which was fantastic...really awesome. Interestingly, the only cleaner they use are PTR's which are cleaned and changed religiously with each showing. They have a compressed air line at the projector to blow out dust. The booth itself is surgery room clean... absolutely immaculate (as is the projection level for 35mm where 20 projectors are running.)It is really awesome seeing two 70 X 5 prints (3D remember) coming off the platter and going through the projector and back at such a speed.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 07-27-1999 03:13 PM

Imax prints can last several thousand passes and yes they do scratch. As mentioned the scratches and cinch marks run horizontally on the screen and of a roller is not threaded properly you will get the diagonal hashmarks
Most Imax Films are photoguarded to extend there life and it is not uncommon to run several thousand passes. Because it must rewind the rewind speed (meening theatre owner greed in cramming in extra shows vs buying a second print) contribute to leaving very short cinch marks on the print as wellas loose rewinding. In some of the older theatres such as Ontario Place worse we actually roll the Platters (reels) out the door and down the hall to another room for storage with nasty teardropping.

Dirt is the bigest problem as the registration system uses a vacum to actually suck the film against what is called the field flattner lens (the back lens element in effect)
as such any dirt is left on the glass in the focal plane and shows up on the screen stationary in usually the middle of a bright sky scene
The field flattner is a cylindryical element and is double lengthed and slides up and down against a pair of wiper bars that are covered with a 3m media similar to what is used on the film cleaners. As such the projectionist must watch the screen all the time for dirt
The rolling loop transport does not use the perfs for pulling the film only registering the frame
As the loop forms in the transport a jet of air (typically 52psi)forces the film forward to give it a leading edge like a wave.
The film passes over a minimum of 2 PTRs and in some theatres a brush vacume unit as well with an high voltage antistat.
The original reel unit can be seen in the ontario place cinesphere pictures of the first IMAX projector and is called the MK1
The MK2 can be seen in the Ontario Science Centres Omnimax pictures along with the new Qthru platter system built for Imax by Kinotone
gordon

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 07-27-1999 04:53 PM

How common is treating the IMAX prints with Photoguard? I hate that stuff! Granted, it helps keep them from getting scratched, but I don't like the registration and focus artifacts which come with it. There are a lot of collectors who will fight all day long against Photoguard, as it apprently assisted Vinegar Syndrome. I went through 7 "rejuvenated" prints of Saving Private Ryan and they were all unplayable in my opinion just from the registration and focus alone. Granted, that was 35mm.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 07-29-1999 10:30 AM

Almost 50% are photoguarded especially if they are circuited prints from theatre to theatre

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Sheldon Harris
Film Handler

Posts: 16
From: Chicago, IL USA
Registered: Jun 99

posted 07-30-1999 05:35 PM

Earlier I said IMAX was 70x5...thats wrong....it's 70 X 15..meaning 70mm film and the frame is 15 perfs wide.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 08-02-1999 07:08 PM

The two 15KW lamps are housed one above and one below the actual transport mechanism and both use bifold mirrors to relay the light to the rotar
There are two rotars one located one above the other each carrying its own seperate film one for the left eye and one for the right
The 15K water cooled machines always had the bifold lamphouse It is visible clearly in the Ontario Place Cinesphere photo's. The 4K systems (most were upgraded to 7K) were air cooled and were designed mainly for up to 65' screens.
Over that they went with 12 or 15K lamps
The new SR projector uses 7K lamps and a Kinoton collector
The 15K recitifiers are build by Miller arc welder not ingersol rand. Ingersol builds the aircompressors

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