Film-Tech Forum ARCHIVE: IMAX Basics

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

»	Film-Tech Forum ARCHIVE » Operations » Large Format Forum » IMAX Basics (Page 5)

This topic comprises 6 pages: 1 2 3 4 5 6

Author

Topic: IMAX Basics

Gordon McLeod
Film God

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

posted 08-05-2002 09:45 PM

What type of reel unit did they have the MK1 with the feed and take up reels opposite each other or the MK2 stacked one above the other

| IP: Logged

Brad Miller
Administrator

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

posted 08-05-2002 10:58 PM

MK2

| IP: Logged

Adam Martin
I'm not even gonna point out the irony.

Posts: 3686
From: Dallas, TX
Registered: Nov 2000

posted 08-06-2002 10:39 AM

The air jet scratches will be colored or white, as the emulsion faces the rotor (except on one eye of most 3D films) and should always be in the arrow design pointing to the right side of the screen. Cinch marks from rewinding will be completely random. What Brad describes sounds more like a rewinding issue to me.

| IP: Logged

Brad Miller
Administrator

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

posted 08-06-2002 02:48 PM

These scratches looked exactly like regular black "cinch mark" scratches that could be seen at the ends of reels on 35mm prints, except they were horizontal. That's why I originally thought they were cinch scratches from rewinding. They occupied the entire width (projected height) of the film.

| IP: Logged

Adam Martin
I'm not even gonna point out the irony.

Posts: 3686
From: Dallas, TX
Registered: Nov 2000

posted 08-07-2002 08:04 PM

For the sake of keeping all of this info in one neat place, I shall quote myself from another thread:

quote:

Fantasia 2000, Beauty and the Beast, Treasure Planet, Lion King, and (likely) Aladdin are all "letterboxed" as 1.66 on the 1.4 Imax screen. Apollo 13 will probably follow suit.
Apollo will probably be edited to a certain extent, both for content and length (print cost). 140 minutes X 330 ft/min X .66 $/ft = $30,492 per print.
It would also weigh in at about 900 pounds. My forklift will pick up 1,000 pounds, but you won't see me trying it anytime soon!
There are several modifications for the QTRU reel unit: original configuration will hold about 60 minutes on a reel; for $20,000, the "Fantasia" upgrade will hold about 90 minutes on a reel using the bottom two reel arms; and for another $20,000, the "Apollo" upgrade will hold about 120 minutes on a reel using the bottom two reel arms and 90 minutes on the middle two reel arms with the top arm holding about 60.
The MK2 reel unit with 60-inch reels can hold 90 minutes of film.
The SR projectors are capable of doing a single changeover during a show. A multiple changeover version of the software has been promised, but I don't think it has become anything of a reality yet. That means that an SR with an unmodified QT can run 120 minutes without interruption, or 300 minutes with a full blown QT package. When it comes to feature-length 3D films, both projectors run simultaneously, so no changeover is possible.
The GT and Classic are single-projector systems and, obviously, cannot do a changeover without a second projector. They are limited by their reel unit.
There is also a question of sound system capacity. Theaters with dubbers have to upgrade to a digital playback source at some point. Only so much 35mm fullcoat will fit on a reel.
With all that said, Waikiki Imax is a GT 3D system (probably with a QTRU and a MK2). Polynesian opened in 1991 and is 2D only, so my guess is that it is a Classic with a MK1. The Bishop Museum will have an SR dome and a QTRU when it opens in 2004.

| IP: Logged

Gordon McLeod
Film God

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

posted 08-07-2002 08:47 PM

Several theatres have place a cinemecanica tower beside the dubber to handle longer lengths of mag

| IP: Logged

Adam Martin
I'm not even gonna point out the irony.

Posts: 3686
From: Dallas, TX
Registered: Nov 2000

posted 11-28-2002 12:28 PM

Time to bump up again. [Smile]

Here is a photo of the SR projectors in Grand Rapids. They are motored back from the port window for threading in this view.

Here is a photo of the GT projector in Sacramento. A little bigger. [Smile]

Here is a photo of Gordon threading the Classic in Toronto's Cinesphere. It is Imax projector serial number 1.

The Imax Dome/Omnimax projector is identical to the Classic, except it is mounted on an elevator and run up into the center of the seating area from below. In a dome theater, the projection booth is below the audience since the screen is above.

These are the PPS speakers for the SR system. They are bi-amped. All six channels are the same speaker: L C R LS RS and Top.

These are the PPS speakers for the GT system. They are tri-amped. Again, all six channels are the same speaker.

The sub array for the SR system has six 18-inch speakers. The GT has eight. With the DTAC audio system, there is a discrete sub channel as well as an LF extension from the stage speakers.

| IP: Logged

Daryl C. W. O'Shea
Film God

Posts: 3977
From: Midland Ontario Canada (where Panavision & IMAX lenses come from)
Registered: Jun 2002

posted 11-28-2002 03:04 PM

Bump for Adam's pics... neat!

| IP: Logged

Tristan Lane
Master Film Handler

Posts: 444
From: Nampa, Idaho
Registered: Feb 2002

posted 12-28-2002 02:17 AM

Yet another Bump for one of my friends who was curious about the kind of speakers used in IMAX facilities. (Kudos on the pics Adam)

I especially like replacing speakers in those bad boys. HF seems to be the least accessible. And seems sonics like to cinch down those drywall screws pretty well. Have your cordless handy.

I never responded on the solution to the DTS - Dubber switching dilemma. I ended up using a High Quality Printer switch from the local computer supply store (tried to find a "shielded" model). I used a manual switch because I was concerned that an automatic or electronic switch might produce some random noise in the channels. After a lot of soldering on 25 pin D-subs it was complete. Even had room on the plug to add the SMPTE timcode from the projector and send it to both units through the switch. So far the unit has worked great and I bought a spare just in case.

-T

| IP: Logged

Michael Brown
Phenomenal Film Handler

Posts: 1522
From: Bradford, England
Registered: May 2001

posted 12-28-2002 04:20 PM

Interesting. I was overhearing someone trying to explain why IMAX films are only 45 minutes long. They were saying that since IMAX is such high quality, after 45 minutes you would start to feel nauseous because you were seeing so much information.

hmm ????

| IP: Logged

Adam Martin
I'm not even gonna point out the irony.

Posts: 3686
From: Dallas, TX
Registered: Nov 2000

posted 12-28-2002 10:01 PM

Because of the speed at which the film travels (about 336 feet/minute), a 45-minute film is about 15,000 feet long. This takes up about as much space on a platter as a feature-length 35mm print. Current cost for 70mm lab work is about 66 cents per foot, making that 45-minute print a $10,000 investment. Double that for a 3D film. And that's just for a single release print.

Combine that with the fact that the format is used mostly for institutional documentaries and such, which translate well as short subjects, and you have a 35-45 minute standard.

Giant sized screens with super-fine focus can be a little overwhelming, and that is a concern, but not the real reason.

With the right equipment and modifications, Imax theaters are now easily able to show up to 150 minutes uninterrupted in single-projector setups and 300 minutes in a two-projector SR setup.

| IP: Logged

Brad Miller
Administrator

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

posted 12-28-2002 10:05 PM

Adam, is there no way to keep a film running continuously via a pair of SR projectors? It would seem once the first platter's worth of film is run through and the changeover has been made that the projector could be pulled back and reel 3 threaded. ...or am I completely wrong here? (I've not had the opportunity to work with IMAX yet.)

| IP: Logged

Adam Martin
I'm not even gonna point out the irony.

Posts: 3686
From: Dallas, TX
Registered: Nov 2000

posted 12-29-2002 12:26 AM

The SR changeover was designed to accommodate Fantasia 2000, which was do-able with existing equipment that could handle up to 60 minutes per half. This was achieved with a (not-so) simple software change. Beauty and the Beast was the second feature-length film and was also under the 2 hour limit, as is The Lion King.

The "Fantasia" upgrade for the GT projector involved upgrading (or purchasing, since many GT systems did not have one) the QTRU reel unit to handle up to 90 minutes on one reel, which satisfied the need to run the Disney products without interruption.

The way the SR projectors are tied together as master and slave (only the right projector actually communicates with the PLC and it kind of acts as a proxy for the left projector) currently prohibits a second changeover. In fact, once the first half of a feature-length show comes to a stop on the right projector, it must be left alone until the second half has completed on the left. Otherwise, the system will emergency stop, thinking that a safety switch was opened on a running projector.

With the advent of the QTRU upgrades (now up to 150 minutes because of the DMR product), it is not necessary to make changes on the SR system other than upgrading the reel unit with the longer arms. This is the preferred method anyway, since (eventually ... someday ... no, really) there will be a feature-length 3D film which will require the use of both projectors at the same time. (This was supposed to be Shrek repurposed into 3D, but Dreamworks apparently chickened out after changing their collective mind repeatedly.)

There is supposed to be a "continuous changeover" software upgrade on the drawing board, but with other options already available which also work for the other projectors, the SR software doesn't rank very high on the priority list.

Besides ... if it's longer than 150 minutes, it's a pretty good candidate for an intermission anyway.

Sidebar: The SR system was not designed with a changeover in mind. It was designed as a much-less-expensive-than-the-GT alternative for small Imax Dome theaters and small Imax 3D theaters. Minor "personality glitches" in both the changeover software and the DTAC audio software were still being worked out well into the run of Fantasia.

| IP: Logged

Adam Martin
I'm not even gonna point out the irony.

Posts: 3686
From: Dallas, TX
Registered: Nov 2000

posted 12-29-2002 12:54 AM

Those speakers are great fun to work on. There are no less than 19 screws holding each back panel on, then four screws to remove the midrange to gain access to the HF, which has three screws on the cover and then three more holding the diaphragm in. I lost count.

The most fun I ever had was changing an HF diaphragm on the center channel during a showing of Space Station. I got to the midrange (which faces the back of the cabinet and gets really loud when you take that back panel off!) just in time for a shuttle launch. [Eek!]

At least I had the sense to take my ear plugs up with me.

| IP: Logged

Gordon McLeod
Film God

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

posted 12-29-2002 11:58 AM

One of the main reasons for the approximately 40min running time is that most museums (which is where the money is in the Large Format World) want to schedule shows around an approximate 1 hour turn around

| IP: Logged

All times are Central (GMT -6:00)

This topic comprises 6 pages: 1 2 3 4 5 6

Printer-friendly view of this topic

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.