Film-Tech Forum ARCHIVE: What is the proper loop size for a Century projector?

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Posted by Justin Hamaker (Member # 2165) on 05-06-2008, 03:28 AM:

It dawned on me tonight that I have never tried to find the proper "loop" size for a Century projector. I've been operating two of these machines for about 3 years. Prior to that I had always operated Simplex 1050s or Simplex Millenniums.

I understand the purpose of the loops and I know that too big can cause scratches too small can actually pull open gates. I have never had either problem on the two Centurys I operate, but I would like to know what is the proper size. I don't know the exact model, but looking through the manuals on FT, the MSC looks right.

Posted by Sean McKinnon (Member # 612) on 05-06-2008, 06:18 AM:

I have found that you can set the top loop by opening the pad roller and loosely wrapping the film around it. I do the same thing with the bottom loop but make it a sprocket hole or two larger. I prefer smaller loops. A lot of co-workers over the years complained that I made my loops too small but my machines ran quieter, I had less threading problems, and never got those annoying "standing" scratches on any of the prints I ran. When I would come in on a day off I would see all the loops slapping around the top of the machines, getting scratched, and running louder than the engine on my old Camaro!

Posted by David Zylstra (Member # 4230) on 05-06-2008, 08:05 AM:

An old Century tech once told me that the pad rollers were meant to be the reference point for setting the loops (maybe by design or by accident, only the original engineers know).

To set the proper loop size under the intermittent I originally counted frames from the aperture to the solar cell - this verified the proper lower loop . . . . I found that if I inserted my finger inline with the shoe pivot and thumb stud it gave the right loop which was slightly larger than loosely around the pad roller. The mylar leader I used had numbers on it and there were indicators where the soundtrack was - i.e. threading with a number at the aperture you would have a diamond on the frame at the solar cell.

I also found the same thing as Sean - with proper loop size the Century would run quieter.

Posted by Tim Reed (Member # 137) on 05-06-2008, 08:07 AM:

According to the original manual, the open pad roller arms gauged the loop size.

Posted by Sean McKinnon (Member # 612) on 05-06-2008, 11:46 AM:

How many ways can three people say the same thing [Big Grin]

Posted by James Westbrook (Member # 3690) on 05-06-2008, 12:05 PM:

The fellow who trained me "all those years ago" told me "2 fingers for the loop". After my first few threads, "2 fingers, James. Not your whole fist."

Posted by David Zylstra (Member # 4230) on 05-06-2008, 12:29 PM:

quote: Sean McKinnon
How many ways can three people say the same thing

LOL . . . . . The triumvirate has spoken, it is law . . . . at least we didn't have 3 conflicting answers like most questions do.

I was also originally taught 2 fingers, but after a little learning found 1 to be more inline with the proper distance from picture to sound reader (at least with my fingers).

Posted by Sean McKinnon (Member # 612) on 05-06-2008, 04:06 PM:

The problem is that even if your teachers two fingers created the perfect loop I bet your two fingers, and my two fingers, and brads two fingers are all different sizes which throws any consistency out the window! "2 Finger Rule" = Wrong! [Wink]

Posted by David Zylstra (Member # 4230) on 05-06-2008, 04:57 PM:

Yep, after a little experience I realized how inconsistent 2 fingers was and started studying on my own . . . . that's why I always taught my "students" that the analog soundtrack is 21 frames ahead and they should learn for themselves how to get the proper distance between picture and sound (some people's "2 finger" methods would end up with 22 frames) . . . . . we also always used leader with a countdown and with 10 at the aperture there was a diamond on the frame at the sound reader (the number 10 was also the 7 second point for dowser open timing on automation start).

Another key thing on the Century was returning the framing to center if you had to adjust for a bad splice.

Posted by Tim Reed (Member # 137) on 05-06-2008, 05:12 PM:

quote: Sean McKinnon
How many ways can three people say the same thing

I didn't see it that way.

You said, "I have found..." which indicated you weren't sure if it was the "right" way or not. Then, David said, "An old Century tech once told me..." denoting second-hand information that could've been a wive's tale for all he knew.

I referenced the manual for a definitive answer. [Wink]

Posted by Steve Guttag (Member # 268) on 05-07-2008, 12:24 AM:

Please note on the Century pad roller thing...it is up to the Tech or <gulp> the factory to set how far the pad roller arm swings open...so your loops may vary.

Steve

Posted by Justin Hamaker (Member # 2165) on 05-07-2008, 02:39 AM:

I took a closer look at this at work today and realize that my top loop was about right, but my bottom loop has been probably 2-3 frames too big. I'm glad I asked this question.

Posted by Brad Miller (Member # 2) on 05-07-2008, 02:42 AM:

An easy rule of thumb with Centurys is to say that with the lower loop in its smallest position (just before the pulldown of the next frame) the distance from the inside of the loop to the intermittent shoe pivot point should be just big enough to stick a Sharpie marker in there.

Most people make that loop WAAAAAAAAY too big.

Posted by Steve Guttag (Member # 268) on 05-07-2008, 06:29 AM:

I've found that if the bottom loop size is correct, it won't bounce up and down like mad but tend to hold its shape like a Simplex will.

Steve

Posted by Sean McKinnon (Member # 612) on 05-07-2008, 02:26 PM:

Yeah, I guess you're right tim. I was under the impression that only the Century "C" manual said that about the loops which was why I was unsure of saying "according to the manual."

I have found, [Smile]

on Simplex machines that making your loops so that they come between the top of the "bolt" in the middle of the sprocket in it's lowest position and level with the top of the sprocket in it's largest position worked well, and ran very quiet.

Posted by Louis Bornwasser (Member # 3063) on 05-07-2008, 06:50 PM:

The geometry on the C and the SA is the same, so loops would be the same. Remember the size of the lower loop is your only opportunity to adjust the optical sound/picture sync. Tight loops for very long throw houses; the reverse for short throw.

When we did a large number of premieres in the 80's it was common to find that even very experienced people made the loops WAY too big. Gunshots were "delayed." Louis

Posted by Kenneth Wuepper (Member # 1174) on 05-07-2008, 08:20 PM:

Most present threading leaders have a built in sync check for the sound threading. When a number is in the gate and at the aperture behind the lens, the diamond should be at the slit of light in the reader.

The amount of film between these limits will be your determining factor in proper threading. I usually count the number of frames in the loop below the intermittent and place that information on the projector casting for future reference.

The upper loop will also determine sync of the digital sound if it comes from an upper reader. The number of frames in the path from the upper reader to the analog slit must be consistent or there will be some nasty sounds when the digital reverts to out of sync analog.

KEN [Wink]

Posted by Robert Throop (Member # 61) on 05-08-2008, 09:11 AM:

If I'm not mistaken the diamond on the leader is 20 frames ahead of the number. Dead sync is 21 frames which would be correct for a drive in. 20 frames would be right for someone sitting about 40 feet from the screen. very large houses require a smaller loop.
Bob

Posted by Michael Moore (Member # 3867) on 05-08-2008, 09:26 PM:

You know I never really paid overly too much attention to the size of the loop other then make it so it was not to big or not to small. My rule of thumb is that if I look directly at the loop the film splits the oil window on the intermittent housing perfectly in half. I do this with the frame knob dead center (as close as possible) and just make sure the intermittent is in the dwell position. I also have never had delays or sync issues with sound, even if the loop is too big or too small then again our house is only an 80 foot throw.

I find on the SA Century I have if I use the pad rollers as a guide the loops are too small. I find the top is about one sprocket hole bigger then what the pad roller makes, and the intermittent is about 3 sprocket holes bigger.

Mike

Posted by Tim Reed (Member # 137) on 05-08-2008, 11:15 PM:

Robert, the optical track for 35mm is advanced 20 frames ahead of the picture.

Posted by Jeffry L. Johnson (Member # 453) on 05-10-2008, 01:47 PM:

Robert is correct.

SMPTE 40, "SMPTE Standard for Motion-Picture Film (35-mm)-- Release Prints--Photographic Audio Records" specifies 21 frames +/- 1/2 frame.

The projection leader indication of twenty (20) frames places sound/picture synchronization about 50 feet away from the screen.