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Topic: Aperture plate filing

William Dickson
Film Handler

Posts: 41
From: Riverside, Ca. USA
Registered: Jan 2000

posted 01-27-2000 04:43 PM

I recently noticed that many of the appeture plates in our theater need some minor filing. The projected images have slight inward bulges on the sides. It doesn't appear to be caused by scope lenses not alligned properly. Any tips on how to file the appeture plate would be greatlt appreciated. Also what type of file should I use?

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Dave Williams
Wet nipple scene

Posts: 1836
From: Salt Lake City, UT, USA
Registered: Jan 2000

posted 01-27-2000 06:54 PM

Use a nail file. Most files from the hardware store are so heavy they will file the shit out of it.

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"If it's not worth doing, I have allready been there and done it"

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John Walsh
Film God

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

posted 01-27-2000 10:42 PM

Did you mean the 'shadow' bulges inward, rather than the 'image?'

You might find that cutting a strip of emery cloth and lightly running it on the opening edges will remove just enough brass to clean any shadow away.

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 01-27-2000 11:39 PM

If you absolutely MUST file that plate a bit, go spend some bucks on some real aperture files. The files you can find at Sears are rough on all edges, and while you are working on a corner, you will be cutting into the next side! Also, remember if you're wanting to open up the top right corner as it is projected on the screen, you want to cut on the lower left hand corner of the plate, as the lens flips the image.

Before you go cutting on a scope aperture, check out the "Focusing Anamorphics" tips on the front page of this site. Many times the focus will get just a touch off and will "shrink" the image on screen to produce a shadow.

Finally, remember that once you file, there is no way to put what you cut back! So be reeeeeal careful.

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John Pytlak
Film God

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

posted 01-28-2000 09:16 AM

Whatever you do, always use the SMPTE 35-PA (RP40) test film to verify that you are projecting as close as possible to the correct image dimensions.

Per Standard ANSI/SMPTE 195, the projectable image area for "scope" is 0.825 X 0.690 inches (20.96 X 17.53 mm). The projectable image area for non-anamorphic (1.85:1 aspect ratio) is 0.825 X 0.446 inches (20.96 X 11.33 mm). The 1.66:1 aspect ratio is 0.825 X 0.497 inches (20.96 X 12.62 mm), and the "Academy" 1.37:1 aspect ratio is 0.825 X 0.602 inches (20.96 X 15.29 mm).

Test films and standards are available from the Society of Motion Picture and Television Engineers, http://www.smpte.org

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Professional Motion Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

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Martin Frandsen
Master Film Handler

Posts: 270
From: Denmark, Europe
Registered: Jun 99

posted 01-28-2000 02:02 PM

I do not have a loop of RP40 test film, but i found some RP110, i think its for the same use, checking correct image dimensions when you have been filing appeture plates, it shows the different aspect ratios.

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Gordon McLeod
Film God

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

posted 01-28-2000 02:08 PM

Get a set of needle files for the fine work and Iuse an AugerBit file for the course work

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John Pytlak
Film God

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

posted 01-28-2000 02:30 PM

Martin:

Some of the SMPTE 35-AT (RP110) test film that is in circulation is quite old, and was made before the current dimensions were adopted. In particular, the anamorphic image width has been narrowed from 0.839 to 0.825 inches, and the anamorphic height has moved from 0.715 to 0.700 to 0.690 inches. Using the old dimensions risks showing the DTS track on the screen, and will show more "flashes" at splices.

I believe SMPTE is updating RP110 and the 35-AT film to agree the current dimensions specified in ANSI/SMPTE 195 and RP40.

I suggest you get some new SMPTE 35-PA (RP40) so there is no question.

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Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99

posted 01-28-2000 05:39 PM

I have had some apertures that have those little humps in them. They look like dust bunnies that won't go away when you clean the aperture.

If that's what you have, may I suggest using an emery board nail file?

I find that they have just enough 'bite' to get the burrs off the edges of the plate without the risk of over-filing and ruining the plate.

Ask one of your box office cashiers for one. They have LOTS of them!

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Rick Long
Jedi Master Film Handler

Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999

posted 01-30-2000 06:54 PM

Many technicians, over years of installing projection equipment, have developed a theory which states that light enlarges the hole in the aperture.

This must be the case. When we leave a theatre, the plates fit the screen perfectly. When we go back to the theatre, a month later, the picture is on the masking in many cases. Although there is a cheap file covered in brass dust on the port-hole ledge, the projectionisit invariably denies that anyone tried to improve on the plate.

Thus, light wears holes in aperture plates.

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John Walsh
Film God

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

posted 01-30-2000 08:02 PM

Yes! The light photons push the brass filing away from the projector....

In this part of the universe, however, I find that the hole gets smaller. I think the action of getting hot, then cold, then hot, etc. closes the hole slightly.

Also, in new theaters, as the floor settles, the projector might tilt down just a little. That causes a very slight shadow, usually at the top, after a few months.

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Tim Reed
Better Projection Pays

Posts: 5246
From: Northampton, PA
Registered: Sep 1999

posted 02-03-2000 09:08 PM

STOP! Do not file your plates, yet! Check the masking limits.

Assuming your pictures started out okay, and since aperture plates don't grow, it is a good idea to make sure the masking stops haven't slipped. Put up some target film and see exactly where you are. This will tell you much.

Good luck!

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Martin Frandsen
Master Film Handler

Posts: 270
From: Denmark, Europe
Registered: Jun 99

posted 02-06-2000 05:03 PM

I like when the picture 'overlaps' the black masking around the screen just a bit. Are there any SMPTE 'rules' regarding this? in some theaters the picture is WAY in to the black masking and it just dosent look right.

Martin

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John Walsh
Film God

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

posted 02-06-2000 06:14 PM

Tim's got the right idea: check it first.
There are no SMPTE standards for how much should overlap onto the masking. But, it would be hard to define that. If the aperture is close to the film, you can get a pretty sharp transistion from "white light" to black. If it's far away, you may need to file it out more to insure there is no shadow on the screen. Centurys seem to hold the film away farther than Cinemecannicas, so you need to file Centurys a little more.

Picky people want it as little as possible, but generally will accept about 6" of spill. I personally would allow up to 12" because I had too many screens to keep running, and don't want to come back to places where the bottom masking drooped, or the projector settled, etc. Except for 70mm runs, where I would keep it at 6".

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Tom Kroening
Expert Film Handler

Posts: 214
From: Janesville, WI USA
Registered: Oct 1999

posted 02-07-2000 12:57 AM

Hey I'm a little confused by a problem im having. We moved a flat format print into one of our booths this week. We havn't had a flat print in there for months (since before i was a projectionist). I changed the lenses and the plates. The image fills the screen on one side and angles inward so on the left side of the screen there is dark space on the top and bottom of the screen. The aperture plate is perfectly straight on the top and bottom, i even swapped it with a plate from another projector and i get the same results. The projector is at angle to the screen which could be causing this. Anyone know how to fix it?

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