This is topic 70mm filmwinds on platter in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.


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Posted by Monte L Fullmer (Member # 2797) on 03-18-2005, 02:03 PM:
 
Okey, now I'm gonna play "newbie" on this topic since I've never had the chance to run 5/70mm:

I've noticed on a bunch of picts of 70mm platter winds, that the magnetic side of the print is on the outside of the wind, which means that the emulsion is on the inside side of the wind, or should I do a comparision: the wind is "soundtrack down."

Any special reason for this, or is this the norm for 5/70mm winds.

thx-Monte
 

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Posted by Brad Miller (Member # 2) on 03-18-2005, 03:26 PM:
 
It probably started years ago and just became the norm without anyone really questioning why, sort of like how so many people think that the soundtrack HAS to face toward the screen when threading regardless of what kind of nasty twist it produces. It's retarded.

When I started at Northpark I switched them over to emulsion out winding (oxide in) on their 70mm prints and the warping and focus problems that were present at that time (although minor) went completely away.

Moving to FHF - LARGE FORMAT forum is for 8/70 and up.
 

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Posted by Thomas Dieter (Member # 2507) on 03-18-2005, 05:35 PM:
 
Okay, now it's my turn to play newbie, granted I am one compaired to the amount of time I've been on FT. But, I can still teach alot of people that have had more experience in the booth than I, why certian things shouldn't be done. (see one of my post in AKA outing bad.... for more details)

Sence I've started work at the Picture Show at Altomonte Springs, I have heard more people refer to the sides of the film as Emulsion and Oxide. I don't under stand this, and it wasn't taught to me when I was in training. Naturally, I try to pick up on things, and figure out things on my own. I also hear "Emulsion Scratch" more often than I do anything else. How can you tell what side the scratch is on, with out touching the film? (Light Reflection?)
 

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Posted by Gordon McLeod (Member # 33) on 03-18-2005, 05:55 PM:
 
The emulsion side has a geletan emulsion containing eithera dye based or silver based image
the oxide for magtracks is applied to the base side of the fim
 

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Posted by Darryl Spicer (Member # 711) on 03-18-2005, 06:50 PM:
 
by the color unless it is very light on the emulsion side equals
Very light =black
then it goes into layers
First layer scratch = green
Second layer scratch = yellow
third layer scratch = white

Base side scratches are black and can be light or very dark based on how hard the scratch
 

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Posted by John Pytlak (Member # 331) on 03-18-2005, 07:04 PM:
 
Photographic film has a gelatin emulsion that forms the image coated onto a clear plastic (polyester) base. Here is an on-line book from Kodak that discusses film structure and its physical and photographic properties:

http://www.kodak.com/US/en/motion/support/h1/

http://www.kodak.com/US/en/motion/support/h1/selecting.shtml

quote:

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Selecting Your Films

* Selecting Your Films
* Film Datasheets
* Film Types, Names, and Numbers
* Film Descriptions
* Base
* Darkroom Recomendations
* Exposure Information
* Processing
* Storage of Raw and Exposed Film
* Sensitometric & Image-Structure
* Sizes Available
* Film Identification

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quote: Monte L. Fullmer

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Any special reason for this [winding 70mm film emulsion in/base out], or is this the norm for 5/70mm winds.

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All the relevant standard-setting bodies recommend that triacetate elements be would emulsion in for archival storage, as 'stretching' the emulsion exacerbates the effect of deformation caused by base shrinkage, and emulsion in helps protect the emulsion itself. The same does not necessarily hold true for projection in general, platter use and/or polyester prints, though; and in a projection context, this issue has been flogged to death in many previous threads.

One other reason why 70mm might always have been wound base out is that when you're running it reel to reel, you can't introduce a twist in the film path. So the oxide stripes have to be on the correct side of the film as it is pulled from the feed spool to make contact with the heads in the projector. Since you can only coat the oxide stripes onto the base side of the film, the orientation of the film as it is wound onto a projection spool does have to be standardised, because this affects the design of the film path components related to magnetic sound playback.
 

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Posted by Brad Miller (Member # 2) on 03-18-2005, 07:36 PM:
 
You lost me on that last paragraph Leo. Can you reword? Why can the reel not spin a different direction? This is done all the time on 35mm and 70mm prints.
 

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Posted by Leo Enticknap (Member # 534) on 03-18-2005, 08:00 PM:
 
It's a bit difficult to describe without drawing a diagram! What I was trying to say is that the design of the mag head & scanning drum assembly in a projector needs the film to be entering the mechanism the right way round for the oxide to make physical contact with the head. Furthermore the oxide stripe can only be coated onto the base side. This is unlike with optical sound, with which a combined print can be struck so that either the base or emulsion side faces the projector's lens in order for the image to be the right way round. OK, almost all the combined optical prints you get nowadays are SMPTE, base facing the lens ones: but there are some DIN prints still kicking about. As far as the projectionist is concerned, though, getting the optical track the right way round is all (s)he needs to worry about. So in order to minimise the risk of a mislacing screw up, there's no need to standardise whether prints are supplied and shipped with the emulsion or base side facing outwards, because the layout of the film is not symmetrical.

The layout of a 70mm mag print does appear to be symmetrical at first glance. So in order to make sure that the SMPTE 'base facing the lens' orientation is followed through, you need to standardise which way round the mag heads are positioned in a projector's film path. It also helps a great deal to standardise which way round prints are wound onto reels, because at first glance the topography of the film looks symmetrical. As with a 35mm full-gate silent print you have to look a bit more closely to make sure that you're feeding it into the projector the right way round. So sticking to one orientation on reels when shipping 70mm mag prints around offers an extra safety net.

Point taken - the feed spool can be mounted so that the film is being pulled clockwise from 3 o'clock or anticlockwise from 9 o'clock to ensure the correct orientation as the film enters the projector, if necessary. I was just suggesting that the convention of winding 70mm prints one way reduces the chance of anything going wrong.
 

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Posted by Brad Miller (Member # 2) on 03-18-2005, 08:41 PM:
 
Ok then. I've received 70mm films would both directions and it was no big deal to run reel to reel (or on platter) in either direction. Anyone handling a 70mm print had damn well better be far better than simply knowing which way to thread the film so the mag tracks are up against the heads was always the way I looked at it.

BTW, somewhere along the line I ended up with a big chunk of 70mm clear film that had a line down one edge that looked very similar to a 35mm soundtrack line. I started splicing a chunk of that at the head of the framing leader on the prints and we just treated it as if it was a really big 35mm print ("soundtrack line towards the operator") when threading the platter. It made things easier to do the switch from emulsion in to emulsion out operation and offered that extra "safety net" you speak of should an emergency relief guy have to fill in, which never happened.
 

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Posted by Steve Guttag (Member # 268) on 03-18-2005, 09:42 PM:
 
And, of course, the "frame line identifier" that, by SMPTE standards, should always face inboard can be relied upon

There really is no substitute for knowing which is the correct way to thread the film, 70mm or no. By providing "safety nets" you only encourage people to not think and then fail miserably when anything out of the norm occurs.

Steve
 

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Posted by Monte L Fullmer (Member # 2797) on 03-19-2005, 03:00 AM:
 
What was Leo mentioning on winds, is like with me imaging that the platter deck is like a reel with one side of the flanges removed.

Imagine, with the decks turning in the anti-clockwise direction, the reel is "laying on it's side" turning in that anti-clockwise direction. Then, if we take this image and re-align ourselves by looking underneath at the deck's rotation and compare this rotating deck to a standard takeup reel's clockwise rotation on a projector. We would then see where the magnetic striping's position on the deck when it's winding back from the machine, being this deck is that takeup reel laying on its side, in the rotation of that required clockwise direction on the lower reel arm and spindle.

And this is why of my opening statement of "soundtrack down." (or base out..)

Same goes for 35mm "rewinds" and I can almost see why some theatres wind their prints soundtrack down - like an actual clockwise rotation of a takeup reel of a projector.

(if this makes any sense....one have to think reverse on this one).

.....

quote: Thomas Dieter

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How can you tell what side the scratch is on, with out touching the film? (Light Reflection?)

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quote: Leo Enticknap

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All the relevant standard-setting bodies recommend that triacetate elements be would emulsion in for archival storage, as 'stretching' the emulsion exacerbates the effect of deformation caused by base shrinkage, and emulsion in helps protect the emulsion itself.

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quote: Leo Enticknap

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One other reason why 70mm might always have been wound base out is that when you're running it reel to reel, you can't introduce a twist in the film path. So the oxide stripes have to be on the correct side of the film as it is pulled from the feed spool to make contact with the heads in the projector.

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quote: Leo Enticknap

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Since you can only coat the oxide stripes onto the base side of the film, the orientation of the film as it is wound onto a projection spool does have to be standardised, because this affects the design of the film path components related to magnetic sound playback.

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quote: Leo Enticknap

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The layout of a 70mm mag print does appear to be symmetrical at first glance. So in order to make sure that the SMPTE 'base facing the lens' orientation is followed through, you need to standardise which way round the mag heads are positioned in a projector's film path. It also helps a great deal to standardise which way round prints are wound onto reels, because at first glance the topography of the film looks symmetrical. As with a 35mm full-gate silent print you have to look a bit more closely to make sure that you're feeding it into the projector the right way round. So sticking to one orientation on reels when shipping 70mm mag prints around offers an extra safety net.

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I'm sorry, but I don't follow this either. I do find that particularly with polyester prints I sometimes need to look quite closly to see which is the emulsion side, but it would be difficult to mistake which side of a print the mag stripes are on, surely. If the leader is not striped then you only need to pull down to the start of the reel itself to check that you've got it right.

Something I've wondered about in the past: In the 'French' section of MOMI the picture was direct rear projected, i.e. no mirror. Was a special reversed print made for this, or was it a special projector, with the sound head on the opposite edge? Acording to a book that I've got the sound head on the GBN portable could be reversed to read from either edge of the film for this purpose.

Brad,

On this forum the terms 'track up' and 'track down' and often used to refer to the wind of a 35mm print on a platter, and these terms seem to be used to equate to 'emulsion out' and 'emulsion in', or have I got that the wrong way round?

If you were to pick up a print from a platter, and flip it over then the track position would have changed, but not the wind, emulsion in or out. Of course, the print would now be wound in the opposite direction, clockwise/anti-clockwise. If track up or down can identify which way a print is wound on a platter, does this mean that all makes and models of platter always rotate in the same direction?
 

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Posted by Brad Miller (Member # 2) on 03-19-2005, 05:09 AM:
 
Yes all but one platter rotates anti-clockwise. I think that was the Eprad. Gordon would know for sure since the Eprad platter has always been his favorite.
 

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Posted by Gordon McLeod (Member # 33) on 03-19-2005, 09:37 AM:
 
No brad I here that you are buying up all the eprads to replace those terrible AW3
also the one that Rank industries made I think it was called applied energy turned the other way as well
 

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Posted by Darren Briggs (Member # 1071) on 03-19-2005, 06:19 PM:
 
I run 70mm with mag in (emulsion out) to keep lacing the same as for 35mm (same twists etc that rollers are set up for.
This as long as the rollers are aligned well, and the filmis fed onto the take up plate striaght without dragging on the plate edge.
Have had no problems what so ever with this practice and have run probably more than 60 passes of prints like this in the last 2 years.

Darren
 

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Posted by Leo Enticknap (Member # 534) on 03-20-2005, 05:39 PM:
 

quote: Brad Miller (same point also made by Steve Guttag)

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Anyone handling a 70mm print had damn well better be far better than simply knowing which way to thread the film so the mag tracks are up against the heads was always the way I looked at it.

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quote: Stephen Furley

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The negatives which I had returned to me from a lab a few years ago were wound emulsion out; in response to a question from myself somebody replied that negatives are always stored this way.

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quote: Stephen Furley

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I'm sorry, but I don't follow this either. I do find that particularly with polyester prints I sometimes need to look quite closly to see which is the emulsion side, but it would be difficult to mistake which side of a print the mag stripes are on, surely.

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quote: Stephen Furley

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In the 'French' section of MOMI the picture was direct rear projected, i.e. no mirror. Was a special reversed print made for this, or was it a special projector, with the sound head on the opposite edge?

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quote: Leo Enticknap

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Incidentally, I seem to remember someone telling me that mag-striping the emulsion side of acetate elements required the use of a chemical which was so environmentally incorrect that the EU banned it years ago and the mere mention of its name is enough to give the Swampy brigade multiple heart attacks. I don't know how true this is, though.

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quote:

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Analogue tape consists of three primary components: the base film, the magnetic coating and the back coating. The Mylar (polyester) base film is shipped to the plant on industry standard 660mm (28-inch) wide rolls. The coatings are manufactured on site from a variety of different ingredients depending on the application. The magnetic coating, for example, includes the magnetic oxide, binder, lubricants, whetting agent and solvent, and so on. For analogue tape there can be as many as 26 ingredients. Quantegy actually produces 57 different tape products using 16 basic formulae.

Contrary to popular belief few tape manufacturers actually produce their own magnetic particles. These are normally bought in from specialist suppliers.

The mixing of the ingredients is done in the Mix-Prep building. A critical part of the process is to ensure that the magnetic particles are evenly distributed throughout the binder. Another important consideration is to avoid breaking the magnetic particles as this generates non-magnetic particles, which reduces the sensitivity of the tape or creating clumps of particles, which increases distortion. Milling is the first stage of the process and this is done in large diameter drums containing either glass beads, steel balls or even stone pebbles. This can take up to 72 hours for an analogue tape. Video formulations tend to take less time as the magnetic particles are needle shaped and are therefore more easily damaged. The magnetic coating for video is also produced in individual batches whereas audio tape is treated differently.

Having the consistency of flour, the magnetic particles once mixed with the other ingredients, is stored as a slurry ready to be pumped to the coating area. For audio, typically 400 gallons of mix will be produced at a time and this 400-gallon mix is then added to a 1,500-gallon blend tank. This ensures that any variation, no matter how slight, is offset by the much larger quantity of mix already in the blend tank. This is important for consistency. It takes about a gallon of mix to produce a 2,500ft reel of 2-inch tape...

Once the mix has been applied, the magnetic domains in the coating need to be aligned. This is done by passing the through a strong magnetic field that aligns the North and South poles of the magnetic particles down the length of the jumbo tape. Once this has been done the coating is dried by running the tape through a series of large ovens that vary in temperature from 150°F to 100°F. The length of these drying lines, and the speed at which the freshly coated tape travels, varies according to the product (audio or video) being made. Oven lengths vary between 200ft-500ft and the tape travels between 200ft-800ft per minute.

What is remarkable is that throughout the drying process the tape does not touch anything, but is suspended on a cushion of air as it travels the length of the oven.

Once dried the surface of the magnetic coating is calendered. This is done by passing the tape between two rollers, one made from stainless steel and with a mirror like finish, and the other made of paper or plastic with a measured amount of give in it. This literally irons the surface of the tape forcing the binder that has risen to the surface during the drying process back into the magnetic coating and imparting the characteristic gloss like finish to the recording side of the tape...

Back in Opelika, a lot of the work done by the Chemistry Lab is concerned with quality control, both of incoming materials and during the manufacturing process itself. The staff is also involved in research work as well. One of the key responsibilities is to ensure that the correct amount of catalyst is being added to the magnetic coating. With as many as 10 different mixes being use on a shift this has to be constantly checked. Another important criteria is the mix viscosity. This has to be carefully monitored and it is also critical that the mix ingredients are probably dispersed. All these things are constantly being checked.

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