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Topic: Thickness of film stock

Ken Lackner
Phenomenal Film Handler

Posts: 1907
From: Atlanta, GA, USA
Registered: Sep 2001

posted 06-26-2002 05:40 PM

Is 70mm film stock thicker than 35mm? I got a tour of an IMAX booth, and the print on the platter was about as wide as an average 35mm print on a platter, yet it was only a 45 minute show. Were my eyes playing tricks on me, is the film stock actually thicker, or is there some other explanation for this?

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Paul Mayer
Oh get out of it Melvin, before it pulls you under!

Posts: 3836
From: Albuquerque, NM
Registered: Feb 2000

posted 06-26-2002 06:22 PM

Remember each frame in IMAX is 15 perfs--so a 45 minute IMAX film pack will have the same footage as a 135 minute 5-perf 70mm pack. IMAX linear running speed is three times that of standard 70mm.

As for the thickness of the print stock, I'm sure Mr. Pytlak will be along in a bit with the appropriate link to the standard... I don't remember those prints *feeling* any thicker than 35 or other 70mm print stocks but that doesn't mean anything, especially where my fingers are concerned.

Paul
Less gimpy mercenary film/video/IMAX projectionist
"When the money runs out, so does I."

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 06-26-2002 06:25 PM

Did you take into account the fact that the IMAX 15-perf/70mm format is going be 3.75 times longer for a given running time than a 4-perf/35mm print, assuming the same fps?

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Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

posted 06-26-2002 06:57 PM

The IMAX system pulls about six feet of film per second thru the projector. So thats 360 feet per minute. That's 16,200 feet in 45 mins. 35 runs around 1.6 feet per second. 100 feet per minute, 16,000 feet eaquals 2hrs. 40mins. of a standard 35 film.

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Phil Hill
I love my cootie bug

Posts: 7595
From: Hollywood, CA USA
Registered: Mar 2000

posted 06-26-2002 09:50 PM

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 06-26-2002 09:58 PM

This isn't specific to the original question, but it's worth pointing out that mag-striped 70mm prints _will_ be thicker than non-striped 35mm film, but the difference is due to the stripes and not the film stock itself.

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Ken Lackner
Phenomenal Film Handler

Posts: 1907
From: Atlanta, GA, USA
Registered: Sep 2001

posted 06-26-2002 10:21 PM

I guess my last choice, is there some other explanation?, is the answer. I totally forgot that the frames are 15 perfs. I guess that would make the print much larger. Thanks.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 06-27-2002 06:05 AM

Kodak VISION Color Print Film has the same nominal thickness for both 70mm and 35mm versions. Kodak VISION Premier Color Print Film is very slightly thicker, because it has more silver and coupler in it. The IMAX rolls were so big because the film transport speed is 15/4 times faster than 35mm at 24fps.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

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Leo Enticknap
Film God

Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000

posted 06-27-2002 04:43 PM

Assuming there's no special factor to make the film stock unusually thick (e.g. a mag track or old two-strip technicolor which is two strips of film cemented together), then, very roughly speaking...

Polyester is thinnest, i.e. you will get four hours on a platter easily
Triacetate is significantly thicker - three and a half hours will only just go on
Nitrate is even thicker still. Needless to say, I've never tried to see how much of it will go on a platter deck, but 1,800 feet (ish) will go almost to the rim of a (supposedly) 2,000 foot spool.

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Bruce Hansen
Jedi Master Film Handler

Posts: 847
From: Stone Mountain, GA, USA
Registered: Dec 1999

posted 06-27-2002 05:05 PM

OK, now here is a strange one: I have a tape splicer that is for 5/70. The film fits snugly between the sides of the splicer. When I put a piece of IMAX film (15/70) in the splicer it will not lay flat, like it is very slightly wider. When I close the splicer (like I am cutting the splicing tape) it cuts a little off the edeges of the IMAX film. It does not do this with 5/70. Has anyone else noticed this, or have I juat been sniffing too much splicing glue? Note: I have tried several pieces of 5/70 and IMAX with the same results.

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 06-27-2002 05:14 PM

Are you comparing apples to apples, that is Estar to Estar? Just eyeballing some IMAX against 5-perf I can see what you're saying but the IMAX stock is (and has always been polyester) while the 5-perf I was looking at was triacetate so I would presume it's the shrinkage of the latter vs. the more dimensionally stable polyester stock. Try comparing 5-perf vs. 15-perf Estar prints; I'll bet both slightly overhang the splicer. AFAIK it's all the same stock.

Interesting however that the splicer designers were assuming a certain amount of shrinkage and designed accordingly so there wouldn't be tape overhanging the edges.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 06-27-2002 10:12 PM

IMAX and other special venue distributors use the same ESTAR base KODAK VISION Color Print Film as would be used for theatrical exhibition. Steve's hypothesis that you were perhaps comparing some older triacetate film that had some shrinkage with current polyester film is a good one. Polyester prints have negligible shrinkage, whereas old triacetate may have shrunk a few tenths of a percent.

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Gordon McLeod
Film God

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

posted 06-27-2002 10:23 PM

There is no difference I regularly use the standard CIR 70mm splicer for adding head and tail scrap to IMAX prints
ps what brand of glue was involved

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Bruce Hansen
Jedi Master Film Handler

Posts: 847
From: Stone Mountain, GA, USA
Registered: Dec 1999

posted 06-28-2002 09:03 PM

I would not think someone designed the splicer I have for shrunken film. I have tried several different pieces of 5/70, and several different pieces of IMAX. always with the same results. I know, this is very strange, and I cannot figure out why this is happening. It would be silly to have two different film stocks that are very slightly different in size. Oh, and the splicing glue, Kodak, of course.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 06-28-2002 09:41 PM

Kodak makes splicing CEMENT for triacetate films, not GLUE.

Splicing CEMENT consists mostly of solvents that dissolve a layer of film base, creating a weld as the solvent evaporates. A GLUE would contain an adhesive substance.

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