Film-Tech Forum ARCHIVE: Problem with Small Emulsion "Dot" Every 3 Frames

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Posted by Patrick Matthews (Member # 2705) on 03-18-2005, 02:00 PM:

I just got a new print in (not a brand new print, just a new one to our theatre) the other night and ran it for the first time and I noticed after the run that about every 3 frames on the soundtrack side of the film that there are tiny littly dots where the emulsion is scratched. There are not numerous ones on each frame, just one, and it gradually works its way down the frame every 3 frames. We are using a Ballantyne Pro 35 and a Potts platter. Any idea as to what would cause this and why it gradually works its way down the frame? It is really bugging the crap out of me!

Posted by Monte L Fullmer (Member # 2797) on 03-18-2005, 02:08 PM:

..somebody built their their bottom loop too big coming out of the trap and gate assembly and the loop was smacking against an object underneath the intermittent assembly.

A common thing with Christie P35GPS if the bottom loop gets built too big. They create these little "tik" scraches.

Another possibility of platter rollers having a burr on the surface doing this "tik" scratch, or it was during a make/break session on the MUT.

Why it's important to make the correct loop sizes on both top and bottom.

-Monte

Posted by Patrick Matthews (Member # 2705) on 03-18-2005, 02:18 PM:

Hmmm...interesting because I made the loop the same size that I always do and I've never had this problem before. While I understand that it would damage the film if it was smacking something underneath there how would it create a dot that moved down the frame, wouldn't it be at the same place on the frame?

Posted by Jeremy Fuentes (Member # 2135) on 03-18-2005, 02:26 PM:

quote: Patrick Matthews
I made the loop the same size that I always do

maybe it was the theater before you, since it wasnt a new print.

Posted by John Pytlak (Member # 331) on 03-18-2005, 02:32 PM:

Look for a roller that has a circumference of 3 (frames) x 0.1870 (perforation pitch) x 4 (perfs per frame) = 2.24 inches, or a diameter of about 2.24/Pi = 0.7 inches. I suspect that it may be a pad roller with a burr doing the damage.

Posted by Gordon McLeod (Member # 33) on 03-18-2005, 02:45 PM:

On the pro35 check for damage on the roller that supports the lower loop under the intermitent if it has a burr on it it will cause damage like that
also the guide rollers in the soundhead

Posted by Brad Miller (Member # 2) on 03-18-2005, 03:19 PM:

Get a virgin trailer and make a good sized loop out of it (such that you can properly drape it over rollers so it does NOT drag over the side/front/top of the projector when running) and let it run for awhile. See if the dots appear and get worse. If you don't see any marks, stop the machine and make the loops bigger and check that. You can rule out your projector pretty quickly that way.

Loops slapping around don't always hit every single frame. Commonly they bounce up and down so that only every other or third/fourth frame hit.

Posted by Darryl Spicer (Member # 711) on 03-18-2005, 07:00 PM:

quote: Gordon McLeod
On the pro35 check for damage on the roller that supports the lower loop under the intermitent if it has a burr on it it will cause damage like that
also the guide rollers in the soundhead

Had an issue with that roller when I ran those machines years ago. Sometimes the roller wouldn't turn and it was wearing the roller down causing the film to want to buckle with the film picture area hitting the inside of the roller.

Posted by Patrick Matthews (Member # 2705) on 03-18-2005, 08:28 PM:

Ok, after watching another run of the film I noticed that this doesn't occur on every reel, but only reels 5-9. Question is, if indeed I did have it threaded wrong or it was something in the projector, like a burr, wouldn't it be on the whole print?

Posted by Brad Miller (Member # 2) on 03-18-2005, 08:45 PM:

Did you build onto large reels (1-4 and then 5-9), then platter?

Posted by John Pytlak (Member # 331) on 03-18-2005, 08:53 PM:

The plot thickens! [Wink]

But most likely a repeating "dig" is caused by a roller having the circumference equal to the spacing between the digs. Do you have an exact measurement of the distance between digs (more accurate than just saying three frames and the spot moves)? Then examine all rollers of that circumference to see if they have a rough spot that could scratch the film.

Posted by Scott Norwood (Member # 30) on 03-18-2005, 10:51 PM:

To continue with Brad's thought--did the print come from a theatre that ran it on large reels with one changeover and misthreaded one machine? Were any/all of the leaders removed when it arrived?

Posted by Patrick Matthews (Member # 2705) on 03-19-2005, 12:59 AM:

Brad and Scott: No, I didn't build up on two reels, I went right from the shipping reels onto the platter. Also, the heads and the tails were all spliced back on, looks as if it was run on a platter before it got to me.

As for the exact distance between them that is going to have to wait until i'm back in the theatre again but i'll be sure to post the distance when I figure it out.