Cellulose Acetate vs. Polyester film base

MattKing said:

I don't think Helen Bach has posted here since 2007. In case she visits anonymously from time to time, I'd just like to emphasize that I miss her contributions, and I'm sure others do too.

Matt

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Me too Matt, that lady really knew her stuff, I've seen her post on other forums since, but I can't remember which.

Phormula said:

I can confirm, PET is more stable than cellulose acetate, does not break at low temperatures, can withstand temperatures up to 60°C and has a lower tendency to attract dust. It replaced celluose acetate for medical (X-ray) applications many years ago.

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Certainly PET is a "Hercules" of sort.

Harman's chairman Howard Hopwood and Simon Galley both commented on serious problems related to the use of polyester film in the imaging industry. They spoke of it's use in outter space and in the now collector's item "The Autowinder" which took a long roll of very thin polyester film.

Howard pointed out a serious problem with this "Hercules" of a film base:

Polyester film doesn't break and so putting polyester film in 35mm cameras
is a very dangerous thing to do...
if you ever get a jam it will bend your camera rather than break the film.

Simon Galley added:

"We got a polyester jam in a machine and it bent a six inch stainless steel roller in half...
it will not break!"

So yes, PET is strong!

Perhaps as with other domesticated "pets", you might want to
keep an eye on "the baby"!

So far as I know IlfordPhoto is the only manufacturer who uttered that using PET based film in 35mm cameras is dangerous.

Interesting Distractions and the Kodak's Double Negative

Marco B said:

Hi all,

I just stumbled upon this link, I think you will find it interesting. Also in the light of the "How film is made" thread:

http://www.motion.kodak.com/motion/...wsletters_filmEss_04_How-film-makes-image.pdf

For the full reference including the other chapters of this document, go here:

http://www.motion.kodak.com/US/en/motion/Publications/Film_Essentials/index.htm

Marco

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Hi Marco,

Thanks for those interesting distractions!
I briefly went through a couple of modules and came up with a few questions for anyone who wants to take a stab at them...
I found mention in this thread and also in first link, pg.32
(pg. 4 of 6 of the pdf) suggests piping is more serious(?) with PET film.. .

"Film base, especially polyester, can transmit or pipe light that strikes the edge of the film and result in fog."
This is corrected for, according to the article, by incorporating "... a neutral-density dye....

Note the "especially polyester" part... but then the article seems to imply that less correction is needed in PET than in celluose films:
"Dye density may vary from a barely detectable level to approximately 0.2.
Higher levels are primarily used for halation protection in
black-and-white negative films on cellulose bases."

I wonder why this would be so.... ?

They go on to mention that "Unlike fog, the gray dye doesn’t reduce the density range of an image; it adds the same density to all areas just as a neutral-density filter would. It has, therefore, a negligible eEect on picture quality."

How is this grey dye density different from a general fog, other than perhaps being neutral and grainless?
Just how great is the practical impact of non-neutral silver fog density on the color of the projected image?

Is it significant at the theater level?

Just curious...
---------------------------

Also, I found this typo... well it probably is more of an authors slip...
everyone would probably notice it so I am hesitant to mention it but just in case any one is really studying this stuff...

MISTAKE in KODAKs PDF on Movie Film:
Second link, Bottom of pg. 58 of original (10 of 14 in the pdf) re:sensiitometry

The wavelengths of light, expressed in nanometers
(nm), are plotted on the horizontal axis, and the
corresponding diJuse spectral densities are
plotted in the vertical axis. Ideally, a color dye
should absorb only in its own region of the
spectrum. However, all color dyes absorb some
wavelengths in other regions of the spectrum. This
unwanted absorption, which could prevent
unsatisfactory color reproduction when the dyes
are printed, is corrected in the film’s manufacture.

Did you see the mistake?

I think the last sentence should read something like:
This unwanted absorption, which could prevent
satisfactory color reproduction when the dyes
are printed, is corrected in the film’s manufacture.

Humm, there are several ways the sentence could be fixed.
Oh well.

AgX said:

So far as I know IlfordPhoto is the only manufacturer who uttered that using PET based film in 35mm cameras is dangerous.

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Simon notes that niether Kodak nor Foma coat consumer 35mm film on PET either.

(I would note there may be isolated exceptions; wasn't HIE on a PET base?)

Just a note Ray on your comments.

Neutral density and fog are not equivalent in any way. Fog affects the characteristic curve, all of the grains, image structure and speed. ND does not.

PE

One thing that keeps confusing me in this thread is that people are using polyester and PET interchangeably. I know I put polyester (not knowing anything about film bases) in the title, probably starting the whole thing.

PET stands for polyethylene teraphalate; it's what water bottles are made of.

Quoted from Freestyle's web site: "The crystal-clear material of the PET support makes the ROLLEI R³ suitable for use as B+W slide film.

The polyester film support guarantees the highest level of archive stability."

I believe this is the same or simular to the "Ester" base used in Kodak's sheet film.

BetterSense said:

One thing that keeps confusing me in this thread is that people are using polyester and PET interchangeably.

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Not really a poroblem. Polyester is a more general term, usually used to refer to PET.


Steve.

From WIkipedia:

Some of the trade names of PET products are Dacron, Diolen, Tergal, Terylene, and Trevira fibers,[1] Cleartuf, Eastman PET and Polyclear bottle resins, Hostaphan, Melinex, and Mylar films, and Arnite, Ertalyte, Impet, Rynite and Valox injection molding resins. The polyester Industry makes up about 18% of world polymer production and is third after polyethylene (PE) and polypropylene (PP).

I used to love Ilford "Autowinder" HP-5. It was on Mylar or Ilford's equivalent, twisted up in a giant pig's tail, was an SOB to make contact prints from, and it had 72 frames per roll.

Photo Engineer said:

Just a note Ray on your comments.

Neutral density and fog are not equivalent in any way. Fog affects the characteristic curve, all of the grains, image structure and speed. ND does not.

PE

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I am probably overlooking something simple here, but could you go a bit deeper into this?
I would never have considered it but the comment by Kodak go me thinking:

"Unlike fog, the gray dye doesn’t reduce the density range of an image;
it adds the same density to all areas just as a neutral-density filter would.
It has, therefore, a negligible effect on picture quality."

So, why doesn't dye reduce the density range but fog does?
Is the density added by fog - added unequally?

We print through a certain amount of general fog all the time...
and like ND, it reduces the light the TD... is the discontinous nature of this fog too servere to allow it to function as an antihalation method...

What if the fog is produced as a separate layer?

What prevents either a general or a specially formed layer of fog from reducing halation, light piping or whatever?

Ray;

Just one quick example then. If you have a film with a curve from 0.2 - 3.0 and add a 3.0 neutral density, you get the same curve from 3.2 - 6.0 with no change whatsoever in curve shape, just a required change in printing time.

With fog, if you have fog of 3.0 added to that curve, you have no image at all!

I rest my case. I think I need not go into all of the other gory details.

PE

Moebius Strips of the Universe

Photo Engineer said:

...the other gory details.
PE

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OK- I probably just need to clear my head.
I'll see if it makes any more sense to me in the morning.

I was thinking about topology last night. Maybe it affected me somehow.
:confused:

kodak 2475 Recording in 35mm was on Estar-AH base. Definitely a tinted base, not clear. Never has hurt any of the cameras I've used it in.

I presume this Estar-AH base was for dimensional stability in the scientific applications, probably by physicists trying to detect sub-atomic particles...

Otherwise, we generally only see Estar (Polyester) base in sheet film.

BetterSense said:

One thing that keeps confusing me in this thread is that people are using polyester and PET interchangeably. I know I put polyester (not knowing anything about film bases) in the title, probably starting the whole thing.

PET stands for polyethylene teraphalate; it's what water bottles are made of.

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Sorry,


Polyethylene (Glycol) Teraphtalate [PET] is the chemical correct designation for a material we commonly call Polyester.
The latter though does actually only mean `many esters´ (in a polymer); from this point of view even the celluloid and acetate bases are polyesters, though never called so.
But those reactive resins and their end-products used for constructive purposes are called polyester too.

To make things even more complicated, PET actually means the pure substance, something not neccessarily used as base material. And for a use as film base the extruded PET film has to be mechanically treated.


Anyway, both designations, PET and polyester are commonly used for those film base materials made out of PET.

Amongst those photographic film manufacturers making their own PET film only Kodak use an own brand name `Estar´. (Agfa once used the brand name `Gevar´.)

I work as a technical service engineer in the plastic industry, I remember that some time ago we sent out a PET resin sample to a company that was making photographic film for medical imaging applications. The business ended few years later, when medical imaging applications moved from images recorded on film to images recorded on CDs and DVDs. PET (polyethylene terephtalate) is just one member of the polyester family, the support of the APS film was made of PEN (polyethylene naphtalate), which is even better than PET in terms of properties, albeit far more expensive. In order to make it suitable for film application, PET is extruded and the film undergoes a post-processing called biaxial orientation, during which it improves its mechanical properties.

i just learned tonight about one of the reasons for the advent of safety film ...
http://www.ohiohistorycentral.org/entry.php?rec=490