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This topic comprises 2 pages: 1 2
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Topic: Cause of bouncy prints?
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John Hawkinson
Film God
Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002
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posted 11-27-2008 12:08 AM
A couple things.
Sally Ann (or do you go by Sally?): It may be that the print is just printed unsteady, which is what's been discussed here (i.e. the image on the film is in different positions with respect to the perforations and the edge of the film). But the other possibility is, for some reason, your projector runs steady with some prints and not others.
To tell the difference, try to project the perforations on the screen (generally by pulling the aperture plate and maybe it depends on which lens you use), and then take something that can stand up straight (a microphone stand is ideal, but a broom propped against a chair will do) and set it up to cast a shadow on the screen over the perforations. Then measure how much the perforations move with respect to the shadow. That's a very good indicator of how steady your projector is.
You can then compare it between prints to see. (Obviously if you're comparing different projectors, then you should measure the steadiness as a fraction of the size of the image, e.g. the displacement of some point divided by the height of the perforation on the screen, or whatever).
Steve's explanation is correct, but we can give a little more detail. The fastest printing machines out there in the labs are contact printers. They take a large sprocket (maybe a 64-tooth?) and run both the negative film and the positive film over the sprocket at the same time, while exposing both to a light. In order that the films sit steady, the film closer to the sprocket has to have a slightly smaller pitch (distance between perfs), because the diameter is smaller (by the thickness of one layer of film). That means that the perforations are usually type BH1866, which is 0.1866 inches in pitch. Regular release prints are KS1870, which is 0.1870 inches (and a slightly different shape hope, but that's not important).
Camera negatives come in BH1866. So if you were printing directly from a camera negative to the release print, you could use a continuous contact printer and you'd be golden. But of course, if you tried to print 8,000 prints on the original negative, you'd wear it out and destroy it.
So instead, you print the original camera negative to an interpositive, and then print the interpositive to an internegative, and print the internegative to the release print. But all of these steps cannot be done on continuous contact printers, because of the pitch issues.
So normally the OCN is printed to the IP, then the IP is printed to the IN via a special printer called a step printer, that advances one frame and then exposes the two pieces of film to each other (sometimes with a lens or other optics in between), and then advances again. Since the two pieces of film are not adjacent on a sprocket, the pitch issues don't come into play. This IN is again on short pitch stock (BH-1866), so it can be continuous contact printed to many release prints.
When the labs are in a rush, sometimes they don't have time or resources to step-print the IN, in which case they'll use a continuous contact printer, and because of slippage on that printing sprocket, you can see unsteadiness.
Now, the above explanation is for a strictly photochemical process. Lots of films nowadays (more than half! Probably more than that!) use a digital intermediate. But I think the same issues are there. A negative is printed from a laser film recorder which is then photochemically copied to an IP, which is copied to a handful of INs, which are copied to produce thousands of release prints.
It may be that they skip the original negative and output an IP directly from the laser film recorder. But still, they need to go from the long-pitch IP to the short-pitch IN.
On very small releases, perhaps the INs are made directly from the laser film recorders.
Anyhow, it's always possible it is something physical. For instance, just like certain kinds of scratching can cause film to bulge in funny ways on a platter (counterintuitive!), they might also make the film run through the gate of your projector in a way that is less steady. Do you use filmguard? Have you tried adjusting the gate tension on your projectors? What kind are they?
This business of contact printing instead of step printing is not always the labs fault. Amazingly, sometimes the studios don't get the final cut of the film to the labs before, say, the Monday before a Friday release. If the labs have to have the films printed by Wednesday so they can be shipped to the exchanges, there may simply not be enough time for them to step print the internegative.
I'm not sure what the rates of production are, but this Playback magazine article said that in 2002, Technicolor Mirabel could do about 800 prints per day. That sounds low to my thinking, but for a wide release of 8,000 prints, you could see why there might not be time to step-print internegatives.
I think continuous contact printers top out at around 400 ft/minute. (24fps is 90 feet/minute) I think step printers are about half as slow, maybe 200 feet/minute? Perhaps there is someone who has better numbers.
--jhawk
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John Hawkinson
Film God
Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002
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posted 11-27-2008 07:30 AM
Oh yes, Marco has a good point. 1.85:1 flat movies are 0.446" high. Scope 2.39:1 movies are 0.690" high. So, assuming common-height projection, your flat lens has to magnify 690/446 => 1.55 times as much.
So, for a given quality of film, the apparent unsteadiness on the screen is almost twice as much for scope. (It's also true that the style of cinematography can have a lot to do with it. Probably nobody notices unsteadiness in The Bourne Identity...)
I mentioned filmguard only because it affects the way you set tension in your projector, because the only way the projector keeps the image stable is to apply friction in the gate. With filmguard, since the film is slipperier, you may need more tension.
--jhawk
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