Issues with filming a cinema screen

[Peter Emery]

I'm shooting a 35mm cinema promo destined for a cinema screen.

 

I'll actually be filming in a cinema and showing the screen in the promo. I'll be shooting at 24FPS and making a 35mm print.

 

I have to separately shoot some imagery to show on the screen that will be filmed. I'm planning to do this on video; to then be projected using a digital cinema projector.

 

Should I be concerned about sync scan issues? I could shoot the video image on at 24fps on a JVC camera. Is that a good idea.

 

Input appreciated..

[Simon Wyss]

You'd need a phase shift gear, that is an electronic control unit which allows you to bring the camera shutter to coincide with the projector. In the worst case the camera exposes while the screen is black (or grey). Arri have it, Panavision has it, specialists offer it.

[Peter Emery]

You'd need a phase shift gear, that is an electronic control unit which allows you to bring the camera shutter to coincide with the projector. In the worst case the camera exposes while the screen is black (or grey). Arri have it, Panavision has it, specialists offer it.

 

Having now shot the project I though I'd answer my own question in case anyone is interested. I shot a cinema screen with a 35mm camera at 24FPS. The screen was projected onto by an industry digital cinema projector. Unlike shooting a TV, set changing the phase shift made no difference to the image. Therefore I just shot it straight. The results were perfect. No phasing. Perfect. image.

 

I'd like to hear thoughts from a projectionist about this?

[Adrian Sierkowski]

Might have something to do with the projector displaying every frame 2x, though I am not sure 1) if digital projectors do this, or 2) if it's even the case. It's 7 30 am and I've been up for a long time. . .but it'd be a place to start looking perhaps?

[Peter Emery]

Might have something to do with the projector displaying every frame 2x, though I am not sure 1) if digital projectors do this, or 2) if it's even the case. It's 7 30 am and I've been up for a long time. . .but it'd be a place to start looking perhaps?

 

Yes I think it is. I think they essentially work the same way as a film projector. The projector is a mysterious black box. Even the projectionist didn't really know the details of how it worked.

[Adrian Sierkowski]

Yeah, I think that show each frame 2x has a lot to do with persistence of vision.. but if that was the case, you are effectively doubling your chances of getting the exposure as the projector would be on, off, on, off for each frame, while the film camera would be on/of meaning, no matter what you are catching part of the exposure from the projector in these combinations:

 

On/Off, Off/On, On/Off, Off(nextframe)On.

 

Again, this is my theory... not fact, but seems to make sense to me (at this hour with this little sleep!)

[John Sprung]

Digital cinema projectors are mostly DLP. The way they work is way different than a film projector. They don't have a physical pulldown between frames, so they don't need a shutter with an interruptor blade, or a shutter at all. They have light on the screen pretty much at all times. The reason for syncing to the projector if you're shooting film is to avoid having the film frame exposed by two successive frames from the projector, producing a double image.

 

The strange thing DLP projectors do is they get their black to white scale by varying the amount of time each pixel (for each color) is turned on. They turn on and off hundreds of times a second, but for varying amounts of time. This is called duty cycle modulation.

 

 

 

 

-- J.S.

[Peter Emery]

Digital cinema projectors are mostly DLP. The way they work is way different than a film projector. They don't have a physical pulldown between frames, so they don't need a shutter with an interruptor blade, or a shutter at all. They have light on the screen pretty much at all times. The reason for syncing to the projector if you're shooting film is to avoid having the film frame exposed by two successive frames from the projector, producing a double image.

 

The strange thing DLP projectors do is they get their black to white scale by varying the amount of time each pixel (for each color) is turned on. They turn on and off hundreds of times a second, but for varying amounts of time. This is called duty cycle modulation.

 

 

 

 

-- J.S.

 

Thanks. I'm going to pass that information around!