Film-Tech Forum ARCHIVE: Thickness of film stock

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Posted by Ken Lackner (Member # 1002) on 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?

Posted by Paul Mayer (Member # 355) on 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."

Posted by Steve Kraus (Member # 476) on 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?

Posted by Darryl Spicer (Member # 711) on 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.

Posted by Phil Hill (Member # 371) on 06-26-2002, 09:50 PM:

Posted by Scott Norwood (Member # 30) on 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.

Posted by Ken Lackner (Member # 1002) on 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.

Posted by John Pytlak (Member # 331) on 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

Posted by Leo Enticknap (Member # 534) on 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.

Posted by Bruce Hansen (Member # 281) on 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.

Posted by Steve Kraus (Member # 476) on 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.

Posted by John Pytlak (Member # 331) on 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.

Posted by Gordon McLeod (Member # 33) on 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

Posted by Bruce Hansen (Member # 281) on 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.

Posted by John Pytlak (Member # 331) on 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.

Posted by Steve Guttag (Member # 268) on 06-28-2002, 09:51 PM:

What is the environmental impact of Kodak's film cement in it's manufacture and use?

Steve

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"Old projectionists never die, they just changeover!"

Posted by John Pytlak (Member # 331) on 06-29-2002, 09:05 AM:

Here is the MSDS for Kodak Professional Film Cement:
MSDS Kodak Professional Film Cement

Are you worried that past overexposure to the fumes has affected your judgement of environmental issues, especially regarding cyan soundtracks? Do you long for the days of cement splicing triacetate or nitrate prints?

BTW, Kodak has supported the development of more environmental alternative splicing cements:
http://www.kodak.com/US/en/motion/support/pp410.shtml

Of course, splices on today's ESTAR base prints are made with tape or ultrasonic weld splicers. Only one of the many advantages of today's polyester base prints.

Posted by Steve Kraus (Member # 476) on 06-29-2002, 09:27 AM:

John wrote:
>Only one of the many advantages of today's polyester base prints.

That you *can't* splice via cement (not that I'd want to) is an advantage? Oh, maybe like the cyan tracks that *can't* be played on traditional equipment would be an advantage?

Posted by Steve Guttag (Member # 268) on 06-29-2002, 09:33 AM:

Actually, I don't mind cement splicing. On acetate films, I'll still do it. With cement splicing, never had one of those pesky tape holes get stuck on the film too!

As for longing for the fumes...not to worry John, I still recone speakers...plenty of noxious fumes there! Heck the solvent is MEK or Acetone....BTW someone mention MEK was banned...I just in the last week saw it a NEW True-Value hardware store in the Annapolis, MD area. I have always used Acetone though...kinda like I've always used Varsol over Kerosene.

Steve

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"Old projectionists never die, they just changeover!"

Posted by John Pytlak (Member # 331) on 06-29-2002, 09:34 AM:

The ability to use ultrasonic splices IS an advantage of polyester base.

Posted by John Pytlak (Member # 331) on 06-29-2002, 09:39 AM:

Steve said: "As for longing for the fumes...not to worry John, I still recone speakers...plenty of noxious fumes there! Heck the solvent is MEK or Acetone"

Some people worry about health and the environment, and at least try to improve it. Others prefer to do things the old fashioned way. At least your attitude is consistent.

Posted by Brad Miller (Member # 2) on 06-29-2002, 03:14 PM:

quote:
The ability to use ultrasonic splices IS an advantage of polyester base.

Oh yeah! NOTHING beats an ultrasonic splice. The other major advantage in my opinion is the fact that polyester base won't shrink over time like acetate tends to do.

Posted by Scott Norwood (Member # 30) on 06-29-2002, 03:54 PM:

Another advantage of polyester-base stock is that it isn't susceptible to "vinegar syndrome" (where the film base turns to acetic acid and begins to self-destruct in an odiferous manner).

The only ultrasonic splices that I've seen are the dreaded "lab splices" which are made on unprocessed stock. One of these days, though, I'll visit Brad's theatre and see his splices....

Posted by Steve Guttag (Member # 268) on 06-30-2002, 12:14 AM:

Some people feel there is a problem with the environment and like to dictate to others how to live whether there is a problem or not. I like to have the highest standard of living (ya only live once) and unless someone can show the the irrevocable damage to society on something (like the human population dying out or something) I don't give up things that work easily.

Bt take it out of enviromental issues for a moment...some day because somebody got injured or even killed at a baseball park, they are going to put up hockey like plexiglass screens, or even corded screens like they have behind home plate everywhere in the park to prevent the balls from flying into the stands because if it "can save just one life or prevent one injury it will be worth it..." When that day comes, I'll quit going to the ballpark because they will take away from the quality of the game. Nevermind the millions of kids and fans that go to the park with their mits to catch a ball (or even a bat) and have a memory of a lifetime. Ya know, if you go to a ballpark, you might get hit with a ball or bat, if you can't live with that for yourself or your family, don't go but don't tell me I should have a compromised experience.

So yes, I am consistant in many different areas and some are not even regarding the environment!

Steve

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"Old projectionists never die, they just changeover!"

Posted by Ray Derrick (Member # 1001) on 06-30-2002, 09:10 AM:

OK, so why not combine safety issues AND the environment.

In this country at some time in the past some idiot stood in the way of a reversing truck (or whatever) and got squished or maimed or something. So some bright spark in some Government department decides let's put a 3kHz beeper that outputs a deafening 130 decibels that will travel for at least 3 kilometers in every direction on the back of every vehicle that might at some time in it's life actually go backwards and might squish some idiot that was not paying attention to what was going on around them.

So now, anywhere you go in the Sydney metro area on any day of the week you cannot escape from those annoying beeping noises coming from some great distance from several different points on the compass. Of course they didn't take into account the fact that the idiot in question may be stone deaf, so one day soon no doubt we will also have some kind of human body proximity sensor that causes the brakes to lock up and the engine to sieze and just in case that doesn't work will release a dose of toxic fumes that instantly kill the driver of said reversing vehicle in order to save the life of our precious idiot.

You want cynical?, I'll give you cynical

Posted by Steve Guttag (Member # 268) on 06-30-2002, 09:36 AM:

Just to be argumentative...

I actually approve of those beepers! Depending on the vehicle, of course. Some trucks (most of them) you are completely blind behind and "hope" nothing is in your way..on those, it is a good idea to have some sort of warning for reverse. I work in an industrial park, with a dozen or so docks pointing at each other...trucks are coming and going constantly...when those beepers go off, you tend to look up to see if you are a target. Heck, the UPS drivers if they don't have a functioning beeper will tap their horn.

Now tell me this, why at gated train crossings, the train has to blow his horn? The only one that is going to get hit is the one that ran through the crossing gate. Personally, I like the sound of train whistles and can determine what type of train is coming often by it's sound. This is important since my regular route home has an "at grade" crossing. If it is a passenger train, it will be quick. If it is a slow freight with 5 engines...best to go home the slightly longer way cuz you will be sitting at that crossing for 15-20 minutes.

Steve

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"Old projectionists never die, they just changeover!"

Posted by Steve Kraus (Member # 476) on 06-30-2002, 10:22 AM:

Back-up beepers for trucks backing into docks etc. makes some sense. But whoever decided they needed to go on front-end loaders that spend half their operating life going backwards makes no sense to me.

As for RR grade crossings, in many places there so many closely spaced crossings and frequent trains that the trains do not use their horns as it would keep an entire town awake all night long. Generally this is the result of a local ordinance as a RR would not take the chance owing to liability concerns. However the FRA has a proposed rule that would override local laws and make whistles (horns) mandatory everywhere and a lot of towns are up in arms about it and asking for wavers for crossings that have been statistically safe or for alternatives such as horns incorporated into the crossing protection signals which would be carefully aimed at the roadway itself.

Personally, I think people who run gates and get clobbered get what they deserve but unfortunately there are times when this results in death and injury on the train or other motor vehicles.

Steve: Another thing to listen for are the old time engineers or traditionally minded younger ones who signal for crossings with a --o- (long, long, short, long), the final long held til the train is on the crossing. Prior to two-way radios the whistle was used for communication (calling back a flagman, say) so the crossing signal had to be distinctive from other signals.

Posted by Ray Derrick (Member # 1001) on 06-30-2002, 10:47 AM:

Steve K, you are absolutely right. Backing trucks are not the problem, it is front end loaders, bulldozers and other such implements that go back and forth constantly that cause the grief.

I live in a semi-rural area on the outskirts of Sydney that is currently being overtaken by an encroaching suburbia. All I ever hear at home is "beep beep beep". Did they have to pick a single tone that is right at the most sensitive frequency of human hearing, did they have to make it soooo loud that it can be heard kilometres distant AND as you say, did they have to put it on vehicles that spend half their working lives going backwards??

Surely a small digital message device that announces "I am reversing, look out!" would be just as effective without driving the entire population of the surrounding suburbs insane.

Steve G, it is not at all like you to be argumentative!

Posted by Steve Guttag (Member # 268) on 06-30-2002, 12:08 PM:

Thats not true!!!

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"Old projectionists never die, they just changeover!"

Posted by Ken Lackner (Member # 1002) on 07-01-2002, 12:48 PM:

Why do some electric golf carsts have reverse beepers!??????

Posted by Adam Martin (Member # 641) on 07-01-2002, 01:13 PM:

So you don't get clubbed.

Ba-dum bum.