Film-Tech Forum ARCHIVE: Another Odd Scratch

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Posted by Robb Johnston (Member # 239) on 05-09-2001, 02:59 PM:

On a simplex 1050 projector with Strong alpha platters I am getting a short horizontal base side scratch 1/4 to 1/3 of the way from the right edge of the projected area. It is always on the same projector. It never shows up on the first viewing, and sometimes not on the second, but always on the 3rd.

The scratch moves up the image slowly (6-10 seconds to scan up the picture) The scratch is maybe 8 inches to a foot wide when projected on a 40 foot wide screen, but has negligible height. After a number of runs, there are multiple of these scratches which becomes very noticible.

I have checked the pad rollers and sound drums, loop size, I have even replaced a number of platter rollers that the base side runs over. The problem remain, but the new scratches are fainter.

I am in need of help.

Posted by Pat Moore (Member # 380) on 05-09-2001, 03:24 PM:

Robb;

This does sound like something related to the platter more than anything else. Do you run off of all three platters regularly, or mainly off of two disks? Does the scratch show up as pretty continuous, or intermittently with the gaps between the first scratches filled in as the number of runs increases? Are the scratches curved or fairly straight?

Initially it sounds like the film is getting abraded on the take-up side of things. I'd check the last roller assembly that feeds film onto the takeup platter very closely. Is one of these rollers particularly hard to reach for any reason?

Just some thoughts to start with...

Posted by John Pytlak (Member # 331) on 05-09-2001, 03:32 PM:

Short horizontal or slightly diagonal scratches are usually either "platter scratches" or scratches caused when the film is not being guided properly and rides up on the flange of a guide roller.

See the recent thread on "MUT Question" started by Dave Bird a few weeks ago to see how misguiding the film as it winds onto the platter during makeup or takeup can cause the rotating platter to rub across the surface of the print, causing nearly horizontal scratches.

Your example of the scratch moving slowly up the image in 6-10 seconds indicates a "roller repeat" that puts the scratches an exact distance apart on the film, usually related to the circumference of the guilty roller. If you can, measure the exact distance between each scratch on the film --- then look for roller(s) having that circumference. It's likely the film was misguided up the flange of one of those rollers, and the roller scratched the print once per revolution. For example, film riding up the edge of a 3-inch diameter roller will have a mark every 3 x Pi = 9.42 inches, and will appear on-screen about twice a second, seeming to move up the image. A burr or rough spot that scratches the film as a 1-inch diameter roller rotates would cause scratches 3.14 inches apart.

Let us know what you find.

------------------
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 Joe Redifer (Member # 3) on 05-09-2001, 03:41 PM:

Sounds like one of the rollers on the take up portion of the platter is too close to the actual platter disc, and that film is rubbing against the spinning disc as it is loading onto the platter. Unfortunately, there is no adjustment to change the height of these rollers. Why not?

Anyway, see what you can do to possibly re-aim that roller up a little to prevent the scratches.

Posted by Brad Miller (Member # 2) on 05-09-2001, 03:42 PM:

Sounds like it could be the final roller on the platter that feeds the film onto the deck is just too low and due to the curl of the film is causing only that portion of the image to scuff on the deck. This assumes you are running soundtrack up. (Another reason not to run it soundtrack down, for then it would be the emulsion side that is getting scratched.) Remember the film should NOT come into contact with the surface of the platter until it is 95% standing straight up. The bottom edge of the film should NOT drag across the surface of the platter deck while it is twisting upright.

I have also seen those exact scratches on a Christie projector with too large of a lower loop, but on a Christie they would be emulsion scratches. (Christie now makes slap guards that screw into place under the Ultramittent to prevent this.) I cannot think of anything on a Simplex that would make that mark on the base side of the film.

But getting back to the point, those motors on an Alpha platter can be positioned lower to allow for more film clearance away from the platter's surface. The only problem with this is that the positioning is how the platters are actually timed! You could end up throwing prints if you move it very much. In the end, I always drill new mounting holes for the rollers on that kind of platter to protect the film from such marks.

Before I forget, take a look at the first reel of the film. Then take a look at the last reel of the film. Do the scratches go away as the movie progresses? If they do, then it is absolutely this last roller. If the scratches are uniform throughout a 2 hour film, then it is something else.

Posted by Randy Stankey (Member # 64) on 05-09-2001, 07:56 PM:

What about that last "up-and-over" roller that's only supposed to be used when you are taking up on the top platter?

I've seen some people who mess up on this roller.

Posted by Robb Johnston (Member # 239) on 05-09-2001, 10:23 PM:

Before I saw any of your responses, I returned to the theatre with the problem projector and picked up a trailer that was removed from that print. On inspecting the trailer, I discovered to my suprise that the scratch was in fact on the emulsion side. Due to the black color of the scratch I falsely assumed that the scratch was base side.

Literally within 2 minutes of that discovery I was told that our maintenance man (originally hired as a projectionist when the theatre opened) had found a screw in the failsafe was a little loose and the film occaisionally hit the screw. The inspection also showed that the scratch was a hole size scratch that was (duh) stretched into a short horizontal line by the anamorphic lens.

It goes to show that we cannot assume anything when looking for the cause of a scratch. Now I must go follow the advice of my green mentor and force myself to unlearn some more.

Robb Johnston

Posted by Paul G. Thompson (Member # 655) on 05-09-2001, 10:53 PM:

Robb, just seriously eyeball the enitre film path through the platter (starting at the pay-out head) and through the projector and back to the take-up platter. Look for any remnants of angel hair or green emulsion stuff.

The right side of the screen would be the non-sound track side of the film. The lower portion of the pay-out fingers of the pay-out head could be causing that. Is the film tracking properly through the fingers and the rest of the pay-out head rollers without climbing or chafing?

Since you have discovered the scratch is on the emulsion side, It leads me to this question:

What kind of fail-safe/cue detector are you using? I have seen some new style proximity detectors adjusted too close to the film, where the film was actually rubbing on them. If you have those style detectors, look at the detectors themselves and see if you can see a wear pattern on them. (There should be NO wear pattern at all!)

Posted by John Pytlak (Member # 331) on 05-10-2001, 07:50 AM:

A base side scratch usually shows as black on the screen. A superficial emulsion-side scratch that doesn't penetrate into the dye layers will also show as black on the screen. A deeper emulsion scratch will be green. A very deep emulsion scratch will be yellow. And a scratch that removes all the emulsion will be white. This is because the emulsion dye layers in print film are like a layer cake: magenta dye on top, cyan dye in the middle, and yellow dye on the bottom:

Microscopic Cross-Section of Print Emulsion

Scratch-Free Presentations