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Shooting film projection on film


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#1 Joseph Curran

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Posted 19 March 2011 - 05:58 AM

Dear Cinematographers,


I am hoping that you could advise me with a film I am making.

I need to film a projected film which will run at 24fps, ideally without any flicker. The camera I will be using is an Arri SR3. I have spoken with one cinematographer who says the flicker will depend purely on whether or not we get the two film devices running at exactly the same time, which makes sense to me, but I thought perhaps someone on this forum may of had previous experience with this.

Would it help to shoot at 25FPS on the camera? My mind tells me no, but please, any advice would be much appreciated.

Many thanks-
joseph
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#2 John Young

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Posted 19 March 2011 - 07:53 AM

A while back most people would use the "Selsyn" interlock system, if you're shooting an actual 16mm or 35mm projector.

I would assume that most people today would use a digital projector, along with a digitally produced image.

You may want to read through this thread: http://www.cinematog...p?showtopic=968
The above topic has some of the same questions answered you ask here. It deals with 16mm projector.
I don't know if I follow you or not; are you projecting 16mm or recording on 16mm?
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#3 Joseph Curran

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Posted 21 March 2011 - 06:29 AM

A while back most people would use the "Selsyn" interlock system, if you're shooting an actual 16mm or 35mm projector.

I would assume that most people today would use a digital projector, along with a digitally produced image.

You may want to read through this thread: http://www.cinematog...p?showtopic=968
The above topic has some of the same questions answered you ask here. It deals with 16mm projector.
I don't know if I follow you or not; are you projecting 16mm or recording on 16mm?



Hi John,

Thank you for the link, there was some very helpful information in there.

I'll be shooting on 16mm a 16mm projection, so projecting 16mm and recording 16mm.

Any more help will be greatly appreciated.

bw\joseph
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#4 Antti Näyhä

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Posted 21 March 2011 - 07:42 AM

Interlocking the camera and projector would seem the only way to get 100% perfect results, but another way to reduce the flicker/pulsing is to accelerate the shutter rate of the projector. Most projectors run at 48 Hz (two flashes per frame) or 72 Hz (three flashes) and have no adjustment for this. A five-bladed "telecine shutter" will increase the flash rate to 120 Hz, and some 16mm projectors even have adjustable shutter rates.

The idea is that when your projector is flashing the image at 120 Hz, any small fps differences between your camera and projector will be evened out and cause much less visible flicker. You will still get double images on most frames, as most of the time the projected frame will change while the camera is still exposing the same frame – but depending on the nature of the footage, you might not even notice.

I can't see how shooting at 25 fps would help, though.

Another old thread.
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#5 John Sprung

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Posted 21 March 2011 - 12:40 PM

Try a little test. Run the projector, and watch through the camera viewfinder, running without film. Start and stop the camera a few times. Do you get double images sometimes but not others? If so, you're starting the camera in different phase relationships with the projector. If the camera runs for a while, do the double images come and go? If so, there's enough speed difference between the camera and projector that the phase relationship changes over time.

Test with the projector at 24 and camera at 25, and you'll see the phase relationship go through a complete cycle every second. You don't want to shoot that way, but it'll show you what you're looking for with phase shifts.

Given a 180 degree shutter in the camera, what you see in the finder shows you the kind of thing that'll go on the film, but remember when you're actually shooting that what you see in the finder is exactly what you *don't* get on the film. So, you want to bobble the switch on startup until the finder shows you the worst phase relationship. That way it goes on film the good way, only one projected frame to each camera frame. You want to see the projector pulldown in the camera finder, not on the film.

Another way to look at it: A projector typically has a two blade shutter with a four position Geneva intermittent sprocket drive. It spends 90 degrees pulling down with the shutter closed, then shows the frame for 90 degrees, goes black to double the flicker rate for 90 degrees, shows the same frame again for 90 degrees, then repeats the cycle with the next pulldown. The camera has the shutter open for 180 degrees, then closed for 180 while it pulls down. You want the 180 when the camera shutter is open to catch the flicker interrupt blade of the projector, not the pulldown blade. So, you want to see the pulldown blade in the finder.



-- J.S.
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#6 Antti Näyhä

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Posted 21 March 2011 - 01:28 PM

Try a little test. Run the projector, and watch through the camera viewfinder, running without film. Start and stop the camera a few times. Do you get double images sometimes but not others?

Have you tried this? I would assume that the double images can be very hard to notice – even downright impossible, if the footage doesn't have a lot of motion.

Then again, using this method you should be able to see the brightness pulsing up and down if the speeds don't match exactly.
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#7 John Sprung

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Posted 21 March 2011 - 03:02 PM

Yes, but the less motion there is, the less it matters, too.




-- J.S.
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