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Topic: Shutter Ghost Question

David Stambaugh
Film God

Posts: 4021
From: Eugene, Oregon
Registered: Jan 2002

posted 02-03-2002 05:46 PM

Assuming I'm understanding it correctly, shutter ghosting refers to a timing problem where the frame is still moving when the shutter opens to pass light through. The symptom is a vertical "tearing" of the image, usually more noticeable in brightly-lit horizontal lines in the frame, or especially in white titles on a black background. Is the severity of shutter ghosting always the same on a projector with this problem? Or would it vary, depending on how the film is threaded from one show to the next? Seems like it would always be the same.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 02-03-2002 06:00 PM

Yes that is the cause and effect
Threading makes no difference to the probldem on most machines

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John Walsh
Film God

Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999

posted 02-03-2002 06:05 PM

Yes, it would be the same, threading wouldn't change anything. Because the shutter is "bow-tie" shaped, the ghosting problem will be more noticable at the top or bottom of the image. That is why the "ghost-test" area on test films is located on the far left/right and at the top/bottom.

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 02-03-2002 07:18 PM

on some machines, it is significantly worse at either extreme of the framing range, a fault of the shutter compensator

Josh

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 02-03-2002 09:02 PM

On an XL, I agree with Josh if the framing rod sticks for one reason or another.

On the Simplex E-7, if the framing slide arm or its associated mechanical parts do not allow the shutter shaft diven gear to re-position after the frame knob is rotated, this can cause the same effect.

For a Brenkert, something has to be busted.

I don't think it is possible for a problem like this to happen on a Century.

For the rest of the projectors, I think I will just stay out of it.

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Stan Gunn
Expert Film Handler

Posts: 176
From: Clematis, in the hills near Melbourne Australia
Registered: Aug 2000

posted 02-03-2002 10:24 PM

I was taught the word BRAT, which means Bottom Retard, Advance Top
If the ghost is at the bottom of screen retard shutter,
If the ghost is at the Top of screen advance shutter.

makes it easy if you can remember the secret word.

------------------
ALL PARTS FOR VICTOR AND KALART VICTOR 16MM PROJECTORS.SERVICE TO 35 AND 16MM PROJECTION EQUIPMENT.
35MM sprockets made to order.

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 02-03-2002 10:33 PM

Stan, that is a good way to remember it. Thanks

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Leo Enticknap
Film God

Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000

posted 02-04-2002 02:16 AM

The other factor which can affect how prone to ghosting (or not) a specific projector is is the size of shutter blades relative to the speed of the pulldown. For example I found that on a Vic 5 with a two-blade shutter, timing it was pretty easy because there seemed to be about half an inch of excess shutter either side of the pulldown, so there was a considerable margin for error. The down side to this is, of course, that the projector is a bit less light-efficient. When I put three-blade shutters on them to run silent prints the blades were shorter - only just wide enough to cover the pulldown, and I'd usually have to make several adjustments to get it right.

A number of projectionist manuals from the teens and 20s I've read describe three-blade shutters in which the blade that covers the pulldown was a lot wider than the other two, thus maximising the lamp output. I can't think of any reason why that wouldn't work with two-blade shutters as well, but I've never seen it done. Is there anything I'm missing?

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Robert Golding
Film Handler

Posts: 65
From: Sutter, CA, USA
Registered: Jan 2001

posted 02-04-2002 03:00 AM

Many, many years ago when I worked for United Artist, I had a century with a single shutter that had a bad travel ghost problem. U.A. wouldn't repair it so I put a 90 degree shutter blade in place of the 80 degree and solved the ghosting problem. The projector itself needed a complete overhall. Presently I have a century with a double shutter (drive in theatre operation) and have had a very slight ghost ever since it was put in. I see it but nobody else seems to.

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Greg Mueller
Phenomenal Film Handler

Posts: 1687
From: Port Gamble, WA
Registered: Jun 99

posted 02-04-2002 09:09 AM

On my DP70 I had timing problems and so I corrected them by unbolting the shutter and moving it forward or rear. I finally got it right. Then I noticed towards the end of the film the ghosting started to reappear. No ghosts at the beginning and ghosts at the end. Hmmm. Turned out it was time for a rebuild on the intermittent. As the projector heated up during the running of the film it would loosen up and begin to ghost. Took me a while to figure it out. But it's fine now.

------------------
Greg Mueller
Amateur Astronomer, Machinist, Filmnut
http://www.muellersatomics.com/

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 02-04-2002 03:51 PM

If there is an "outdoor" shutter on your machine, and it is timed correctly, you could have ghosting equally on the top and bottom of the picture. If so, switch to a 90 degree shutter and your problem will probably go away.

If you have a pulsating ghose on the top or bottom, better check your gear train. I have seen this on occasion in Centrury and XL's several times.

This problem can occur in a Brenkert if the shear key is on the verge of failing.

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Will Kutler
Phenomenal Film Handler

Posts: 1506
From: Tucson, AZ, USA
Registered: Feb 2001

posted 02-04-2002 06:43 PM

Nice thing about ghosting problems on Simplexes...it can be adjusted while machine is operating.

Ghosting on the Christie P 35 GPS means bad/loose jackshaft/shutter shaft belt, possible bad gears and or bad jackshaft/shuttershaft assemblies (usually its the bearings that go). Ghosting w/a Christie means that the show must be stopped, repairs made and the shutter retimed. Repairs can take a few minutes (no more than 10) going balls to the wall! Best way to avoid these problems w/the Christie is to remove the gate assembly and jackshaft sheetmetal cover, clean, inspect and lube belts and gears on a weekly basis and replace worn parts when needed. Christie has improved the the jackshaft/shuttershaft assemblies recently, plus they also have the heavy duty steel gears in place of the stamped aluminum. But if you need to change gears, be careful, Christie LOVES to Locktight those gear set screws and can be a bear to remove!

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Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

posted 02-05-2002 01:59 AM

One of our Century's had a severe shutter problem with the concentric shaft oscillating toward and away from the rear shutter housing. The ghosting was all over, above AND below the credits, plus the speed of the machine became "variable," pulsing in time with the oscillation. Like Paul said, definately a gear-train problem, and wicked one at that. I tried to determine what the cause was, but there was nothing obvious that I could see without ripping the whole thing down. We sent it right back to the seller as it was a rebuilt and had been run less than four shows. The company never actually explained what was wrong, so I just assumed they'd rather not admit that they just left out a gear or two in their rebuiding process! eek!

Anyone have the scoop on "drive-in" intermittents? My recollection is that their pull down was very fast, allowing the shutter to stay opened longer, letting more light thru. In the one DI that I worked I recall that they had cut-down shutters for the DI intermittent but when one died they replaced it with a standard and that caused plenty of ghosting. If I remember correctly, the DI intermittent sprocket seemed to be lighter with holes in the sides as opposed to solid like a normal drive sprocket.

Question is, do these DI intermittents have any downsides? I remember they were really noisy. Any other disadvantages? Seems like if they had no ill side effects, they would be a cheaper alternative than installing a bigger lamphouse in a system that needed a brighter picture, although I would be really hesitant cutting down the shutters....like drilling that first hole in the roof when I installed the sun roof on my car.

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 02-05-2002 02:17 AM

Hi, Frank

Simplex had a high-speed movement for the XL's, and they were quite scarce and expensive. And, wear some ear protectors if you are standing along side the machine....especially if they are worn out.

A downside to them is your splices better be perfect. They will yank a splice apart of the splicing tape is a poor grade, or if you didn't clean the surface before applying the tape.

Whether other manufacturers made them or not, I really don't know....

Paul

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 02-05-2002 08:07 AM

The high speed "Drive-In" intermittents used an additional linkage to achieve a 5:1 pulldown (72-degrees) rather than the usual 4:1 pulldown (90-degrees) of a normal 4-slot starwheel. They were quite noisy, had additional components to wear, and the higher acceleration could stress perforations and splices.

Kodak has just patented a modified 4-slot starwheel design that achieves the faster pulldown WITHOUT an additional linkage. Here is a link to the November 2001 SMPTE Journal paper "Design Improvements for Motion Picture Film Projectors" by DuMont, Kurtz, Silverstein, and Kirkpatrick. This paper describes improvements developed for motion picture film projectors, in particular, new designs for the intermittent, or Geneva mechanism, and for a Universal lamp house. These new designs are intended to improve the quality of the overall screen image as well as light efficiency and uniformity, resulting in significant increases in screen luminance:
http://www.electronicipc.com/JournalEZ/mo/detail.cfm?code=45390010011103 (for SMPTE on-line library subscribers)

Here is a link to the Kodak patent (US Patent 6,183,087):
U.S. Patent 6,183,087

The new Kodak starwheel design can be retrofit to existing intermittents, greatly increasing the efficiency of illumination, in other words, putting more light on the screen!

------------------
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

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