This is topic How to tell where these scratches came from? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Jesse Skeen (Member # 586) on 06-12-2001, 05:24 AM:
At a few different theaters I've seen prints get scratched in ways I can never figure out- most confusing is scratches on the emulsion side that sort of look like diagonal platter scratches, except they're not visible across the entire frame and part of them is green. When projected, these look like there's a flashing green dash moving upwards on the screen. (I've seen this both with Christie and Strong platters).
Another type of scratch I've seen done with Strong platters is a thin vertical line on the base side, and that line is made up of diagonal scratches. I know this is caused by misthreading because it doesn't happen on every film, but I don't know what to tell the people doing it because I can't tell what's causing it.
One other that's got me stumped is diagonal scratches only on the far right-hand side of the picture- you'd suspect this happened during film make-up but it happens afterwards.
It once took me catching someone in the act to figure out where some scratches were coming from- I came in once and saw a green vertical scratch on the screen, then checked the Christie platter and saw someone had threaded under one of the rollers, dragging the film along the screw underneath- ouch!
Posted by Roger Frazee (Member # 640) on 06-12-2001, 06:15 AM:
I have found that diagonal scratches are often caused by misaligned guidance rollers. If film does not lay flat in the roller as it enters and exits, it will rub across the roller as it travels over it. In severe cases it can even ride up on the roller flange.This is why it is essential to check the roller alignment each time the projector is threaded.
Posted by Jerry Chase (Member # 660) on 06-12-2001, 08:04 AM:
Jesse, I think you have the core of a great idea. I would love to see snips of damaged film and an accompanying photo of the cause of the damage, along with a written explanation of how the damage is caused and how it can be prevented. I imagine this could be something where Kodak might even produce a booth chart for distribution to theatres. How about it J.P.? Think something like this would fly? A chart like this could educate a lot of booth jockeys (and managers) fast and possibly prevent a lot of film damage.
Posted by Dustin Mitchell (Member # 372) on 06-12-2001, 08:21 AM:
Roger's absolutely right, roller alignment is the source of many scratches. The scratches on the far right side of the screen you mentioned Jesse sound just like a problem we had at my theatre for a while. The source of the problem-discovered after many damaged prints-was misaligned rollers.
Posted by Brad Miller (Member # 2) on 06-12-2001, 12:55 PM:
Jesse, the first scratch you described can actually be caused by a loop scratch from making the lower loop too big on a Christie (they now have scratch guards installed on all projectors). The other ones you have described sound like that last roller is too close to the takeup deck. Do the scratches get worse and worse as time goes by? If so, you have a roller that is out of alignment. If they just appear and then never get worse, odds are it was an operator threading error.Don't forget to check the two magazine rollers on the projector too.
Posted by Jesse Skeen (Member # 586) on 06-13-2001, 05:57 AM:
I'm pretty sure all of this is being caused by misthreading, and not problems with the actual equipment, since it doesn't always happen on the same projector on every film, and it tends to happen on days when I'm not there. (I don't claim to be perfect, but since the time I scratched a print during one of my very first shifts 9 years ago, I haven't knowingly scratched one since!)
Having photos on hand is a great idea, I've already been looking for a Polariod to borrow so I can mis-thread all the ways I know how and take pictures so the newer people can be sure not to do it.
Posted by Gordon McLeod (Member # 33) on 06-13-2001, 10:05 AM:
I have noticed that often diagonal scratchs are caused by people misthreading a roller and haveing the film sitting up on the flange and the keeper holding it in place
Also on the older Specos the film getting folder into the split of the rollers
the cure Check and Double check
Posted by Joe Redifer (Member # 3) on 06-13-2001, 12:59 PM:
The Strong scratches you describe are caused by misthreading the brain so that the film is actually riding AROUND one of the rollers that surround the payout AFTER the film leaves the payout arm itself. This will cause your black line that is made up of smaller diagonal scratches. We had this type of scratch once and I was blamed, so I had to prove that I didn't do it by scratching test film. I proved that it wasn't me since the first guy who noticed it threaded it up. I had also watched the previous show in that auditorium and it was fine. Ha!
Posted by Tom Kroening (Member # 201) on 06-13-2001, 04:56 PM:
I've seen green diagonal scratches caused by misthreading the platter. It usually occurs when your rewind platter is above your payout platter. Many new projectionists like to go from the brain to the first roller and straight up instad of going down to keep the tension on that first roller. This allows the film to be rubbing on the bottom of the rewind platter as it goes around. As this is only one possible cause for scratching, your best bet is to go through and retrain your staff. Make sure they are consistant with their loop sizes, and always always make them check and recheck when they start the film. I make it a point to teach people to run though all the projectors again after the last show of the set is started.
Posted by John Pytlak (Member # 331) on 06-13-2001, 07:44 PM:
Roger Frazee is correct: Short horizontal or slightly diagonal scratches are usually caused by the film riding up on the flange of a guidance roller. Each revolution of the roller usually produces a scratch at a burr or rough spot. The distance between scratches (the circumference of the roller) is so regular that the scratches seem to march up or down the screen in a regular pattern.Always check to be sure the film is riding "true" on every roller, and that all rollers are turning.
------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
Posted by Robb Johnston (Member # 239) on 06-14-2001, 12:17 AM:
The rising green dash sounds alot like a scratch I had a few weeks back. What Projector do you use? I had the problem on a Simplex 1050. The Friction roller on the Lateral guide assembly of the Sound head was about 12 years old, and had started to crack on the edge. When the crack worked it's way to the surface it made a superficial pin hole scratch into the emulsion. Unfortunately, it was so slight that it was black on screen, but traveled up the picture, and I spent days checking for a burr scratching the base side. It didn't get deep enough to be a green scratch until it ran for a number of days and it had scratches on top of scratches.
Posted by Ken Lackner (Member # 1002) on 09-18-2001, 08:49 PM:
I have seen scratches that look like green dots going straight up the screen vertically, not diagonaly. I have never been able to figure these out. Anyone?
Posted by Brad Miller (Member # 2) on 09-18-2001, 11:27 PM:
Loop scratches from making a loop too big.
Posted by Ken Lackner (Member # 1002) on 09-18-2001, 11:47 PM:
Gottcha. I can picture how that could happen. But why doesn't the same part of each frame get scratched? Why does the scratch travel up the picture?
Posted by Aaron Sisemore (Member # 145) on 09-19-2001, 12:33 AM:
A burr or other sharp part of a roller that makes direct contact with the image area of the film (sound head impedance drums come to mind) can also cause the little green dot scratches. Usually taked 2-3- passes thru the machine to look like they crawl up/down the screen. Either way it needs to be checked out if that is the cause.Aaron
Posted by John Pytlak (Member # 331) on 09-19-2001, 01:28 PM:
Scratches or digs that have exactly repeating distance between them will appear to "walk" up or down the image unless they are an exact multiple of the pulldown distance of each 35mm frame (0.748 inches). If a roller is causing a scratch or dig ("roller repeat"), the distance will usually be the circumference of the roller plus any slippage. ------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion