Film-Tech Forum ARCHIVE: Line Scratching

This is topic Line Scratching in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Chris Byrne (Member # 1563) on 01-31-2003, 09:12 PM:

Nine or so months ago, I came into work to discover a first run print had these hideous vertical line scratches at three different areas onb the screen. Similar to the old war films you occasionally see on TV.

On further inspection, I counted as many as 15 different scratches on the emulsion caused by this obvious misthread.

It had happened before that on another print about 12 months previous to this and after talking to those in the know, I was none the wiser.

I carried out some tests with rubbish film on that particular projector(Kinoton FP30D with basement reader) and found that in 12 different misthreads, the only result that favoured my theory was a misthread around the cowling of the reverse scan reader. That is that the projectionist had missed the first roller after the sound drum and the film had scraped along the metal cowling.

I have put this to some other Techs and they disagree saying that the sound would've been so bad that patrons would've complained. While in essence this is true, I don't know whether or not it could've been a nil session or what?

Does anyone else have any theories or answers to the above.

Posted by Jon Bartow (Member # 241) on 01-31-2003, 09:32 PM:

I know of a couple of chains in the US that run ALL shows, no matter what. Is it possible that this misthread occured when no one was watching that showing? It doesn't have a DTS unit does it?

Posted by Ron Lacheur (Member # 1126) on 01-31-2003, 09:55 PM:

I remember that this happened to one of our prints of Stuart Little 2, it was so bad we junked the print.

Posted by Chris Byrne (Member # 1563) on 02-01-2003, 12:59 AM:

Yeah Jon,

I suspect that if this was the case (nil session), then the operator must have had the monitor turned down. I just can't picture any other scenario.

Also the reverse scan unit is after the gate and would not get picked up on screen until the session afterwards.

Posted by John Spooner (Member # 1565) on 02-01-2003, 09:33 AM:

Dear Chris.
Were the scratches deep into the emulsion itself, also were they linear and parallel, or did they move about?
Also for our information, what are the latest results regards the xenon + cap discolouration.
Rebards, John Spooner. South Australia.

Posted by Chris Byrne (Member # 1563) on 02-01-2003, 07:45 PM:

Hey John,

Yes they were linear and parallel, as though the emulsion was dragging against something fixed (i.e. cowling.)

Xenons are all good at this stage. Am fitting the remaining clamps tonight. [Smile]

Posted by Stephen Jones (Member # 16) on 02-02-2003, 09:16 AM:

Hi Chris,
The problem you are discribing can be caused by a misthread over the cover as I have seen the results of this a couple of times when projectionists new to the Kinoton sound head have mistreaded.But how they get the film there is a mystery as there is a metal piece which is there to prevent this, you would have force the film past it but nothing supprises me these days.The sound would have sounded bad with no digital at all and analog would have sounded garbled.I am running Kinoton FP50D's which have the same sound head as the FP30D. [beer]

Posted by Chris Byrne (Member # 1563) on 02-03-2003, 04:00 AM:

Yeah Steve,

All of our units have the newer style cowlings with that modification that you talk about, however this particular unit has the older style cowling which doesn't!

Posted by Leo Enticknap (Member # 534) on 02-03-2003, 04:38 AM:

As you say, steady tramlines are caused by the film surface arguing with something fixed in the film path. This case sounds like a misthread, but tramlines can be caused by a small, sharp foreign body getting in the film path and these can be a pain to find.

I found that the best way to do it was to thread up about 50ft of 'virgin' stock (e.g. an extra copy of a trailer you ended up not needing), run the motor until it's up to speed, wait 2-3 seconds and then stop it. Unlace the film backwards (i.e. starting at the take-up spool and working upwards), and where the scratch stops indicates roughly the area in which the damage is being caused.

Posted by Chris Byrne (Member # 1563) on 02-04-2003, 08:15 PM:

Leo, that's quite cool! I agree that intermittent faults can be a horse's ass!

Posted by Leo Enticknap (Member # 534) on 02-05-2003, 08:27 AM:

Compliments always welcome! [Smile]

Posted by John Pytlak (Member # 331) on 02-05-2003, 08:54 AM:

When running a scratch test, view the film in a very bright, collimated beam of light, which makes even tiny scratches and abrasions very obvious. I like to hold the film in the projector's projected light beam, or that of a slide projector. A small narrow beam angle spotlight or halogen desk lamp (e.g., http://www.tensorlamp.com/lt590.html )also works well for seeing surface abrasions.

Posted by Brad Miller (Member # 2) on 02-05-2003, 01:08 PM:

Or you could always get yourself a piece of white formica (or perhaps a few pieces of printer paper taped together) and set it on the port window. That should be bright enough. [Smile]

Posted by John Pytlak (Member # 331) on 02-05-2003, 02:25 PM:

Surface abrasions and scratches are easiest to see when illuminated by an oblique collimated light source. So a narrow beam spotlight or the light of a projection beam works very well. Reflecting the light off a surface makes the light more diffuse, reducing the visibility of tiny scratches.

Posted by Douglas Curry (Member # 1485) on 02-07-2003, 09:47 AM:

I have fairly keen eyesight and find the best way to 'find' scratches on a print is to have the light project onto the film at an angle, then rock the film backwards and forwards.. you'll generally see them 'glitter' at you [Big Grin]

Posted by Mitchell Dvoskin (Member # 751) on 02-07-2003, 01:40 PM:

In my travels last summer, I came across a guy who developed and was attempting to market a scratch detection kit. What it consisted of was a roll of 35mm film with special emulsion that glowed under a black light. What you did was load it on to the platter, thread up, and run it for a few minutes. Then, you would unthread, turn off the booth lights, and trace the film path with the enclosed hand held battery powered black light. Any place that glowed that should not would have been rubbing against the film. It made it real easy to find what was scratching.

I could probably find this guy's email address if anyone is interested.

/Mitchell

Posted by John Pytlak (Member # 331) on 02-07-2003, 01:48 PM:

Film with a UV fluorescing dye is a good idea. [thumbsup]

Some also use full coat 35mm magnetic film, which will leave oxide debris in areas causing abrasion. The oxide side also has a mild burnishing effect to smooth rough edges:

http://www.fpchollywood.com/magnetic-film-fullcoat-5-mil-.html

http://www.fpchollywood.com/contactus.html