Film-Tech Forum ARCHIVE: Film tension question

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

»	Film-Tech Forum ARCHIVE » Operations » Film Handlers' Forum » Film tension question

Author

Topic: Film tension question

Sam Hunter
Jedi Master Film Handler

Posts: 779
From: West Monroe, LA, USA
Registered: Jan 2002

posted 01-07-2003 04:05 PM

Some remarks in other threads caused me to wonder if I haven't been damaging my prints using an Nuemade Bench rewinder. I had a majority of my 16mm films collection showing some warping. I couldn't understand why because I keep my film in a closet that I have ran a duct from my HVAC system to and the relative humidity stays around 40% with the temp averaging 65 degrees. Anyway 2/3rds of my films had some warping.
I use this rewinder to give me a tight wind on these films before I store them. Now some folks have stated that there is such a thing as too tight and was wondering if that was possible?
I have gotten out of 16mm now and strickly 35mm and am wondering just how tight should I be rewinding these prints?

| IP: Logged

Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 01-07-2003 06:05 PM

Sam, I could be wrong, but 40% relative humidity might be too low.

Kodak's Publication No. H-50 points out the following on page 13:

quote:
Buckle: Temporary buckle from the loss of moisture from the edges of the film (emulsion and base) when the rolls are stored under dry conditions.

Twist: An effect that is produced in new prints by loose winding of the film, emulsion side in, under dry air conditions. If the film is wound emulsion side out under the same conditions, the undulations do not alternate from one edge to the other, but are directly opposite of each other.

Curl: A type of distortion caused by dimensional differences between the emulsion layer and the support. It results from changes in moisture content of the emulsion layer and support with variation of relative humidity of the atmosphere.

Spoking: A distortion of film on a reel caused by loose winding of film that has a high degree of curl. Perminent spoking is seen as a twist when the film is unwound. Temporary spoking disappears when the film is unwound.

I have not found any real recommendations on what the RH should be kept at in that publication. All it addresses is changing RH conditions and what the effects might be on the film.

| IP: Logged

Gordon McLeod
Film God

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

posted 01-07-2003 08:05 PM

THe GoldE and Goldberg rewinds are probably the worst for cinching film
A good variable speed one is better

| IP: Logged

Sam Hunter
Jedi Master Film Handler

Posts: 779
From: West Monroe, LA, USA
Registered: Jan 2002

posted 01-07-2003 08:26 PM

What is it that damages the film? The starting torque? What would happen if I loosened up the tension?

| IP: Logged

John Hazelton
Film Handler

Posts: 42
From: Oakland, CA, USA
Registered: Jun 2001

posted 01-07-2003 08:47 PM

Alternatively, any reason why one couldn't put a rheostat or variac or something on the motor and ramp up the start speed? I'd love to have some little circuit that engages when the handle is pushed over, and slowly starts the rewind, so the film gets gentler treatment.

| IP: Logged

Gordon McLeod
Film God

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

posted 01-07-2003 08:48 PM

Jaded point there are many good rewinders out there for reasonable cost why reinvent the wheel

| IP: Logged

Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 01-07-2003 09:42 PM

Sam, could you post a picture of the warping? Personally, I don't think that Goldberg rewind caused it unless the holdback clutch was really boogered.....

True - you can have some nasty effects if you simply close the door and trip the start lever. I always gave the reel a spin, and quickly closed the door and tripped the lever at the same time, just like the old pro's did 50 years ago.

The only damage H-50 says about excessive tension is edgewave. But yes - I agree cinching could happen - but that can be minimized with properly adjusted hold-back clutches and proper common sense operation.

The old Goldberg rewinders are still good units. There are many still in service today, and the people who have them will not part with them. I would not hesitate to have one in my booth. I know one that is available, but the only thing I don't like about it is its color. Someone painted it pink.

They are slow in rewinding, but I never remember damaging any film in them in the last 35 years providing there was not a loose wrap on take-up of the projector (where the film would cinch), a goofy hold-back clutch, or there was slack in the film on start-up causing a big "jerk".

| IP: Logged

Sam Hunter
Jedi Master Film Handler

Posts: 779
From: West Monroe, LA, USA
Registered: Jan 2002

posted 01-07-2003 10:08 PM

Here is a couple of samples, its a cartoon short that I have and also a shot of my enviroment as well.
Thanks.

| IP: Logged

Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 01-07-2003 10:40 PM

The first picture looks like major edgewave. It is probably permanent, caused by being wound up under high tension, or if one edge is stressed during film transport.

The second picture looks like twist, but I can't be sure. Please see "twist" in my first post.

I don't think your Goldberg did that to your film, unless the reels were grossly out of alignment and/or the hold-back clutch is practically frozen.

Better check the rest of your collection and take appropriate action asap.

| IP: Logged

Jon Miller
Jedi Master Film Handler

Posts: 973
From: San Diego, CA, USA
Registered: Sep 1999

posted 01-07-2003 11:30 PM

John Hazelton wrote...

quote:
Alternatively, any reason why one couldn't put a rheostat or variac or something on the motor and ramp up the start speed? I'd love to have some little circuit that engages when the handle is pushed over, and slowly starts the rewind, so the film gets gentler treatment.

I have one of those Goldberg beasts, which I retrofitted with a ceramic wirewound resistor (unfortunately I do not recall the exact value, but I think it's a 10-ohm, 20-watt unit) in series with the motor's start windings to soften the start, a la old RCA 1040 soundhead. The rewind now takes about one second to ramp up to speed.

The back tension is kind of a pain to set...unfortunately, I can't get it loose enough to avoid cinching the film pack without the automatic shutoff mechanism getting hypersensitive on me (and this is with an NOS clutch disc). Maybe I should just bypass the auto-shutoff stuff.

| IP: Logged

John Pytlak
Film God

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

posted 01-08-2003 07:58 AM

It looks like the 16mm print was stretched by excessive tension. As others have noted, that old Goldberg winder can have excessive tension and rapid accelerations that will cinch a loosely wound print. For 16mm, the issues would even be worse.

Kodak recommends an ideal of 50 to 60 percent relative humidity in film projection rooms, but the slightly lower humidity of 39%RH that you show wouldn't have caused that problem.

| IP: Logged

All times are Central (GMT -6:00)

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.